(a) Scope and frequency. Calibrate all torque-measurement systems including dynamometer torque measurement transducers and systems upon initial installation and after major maintenance. Use good engineering judgment to repeat the calibration. Follow the torque transducer manufacturer's instructions for linearizing your torque sensor's output. We recommend that you calibrate the torque-measurement system with a reference force and a lever arm.

(b) Recommended procedure to quantify lever-arm length. Quantify the lever-arm length, NIST-traceable within ±0.5% uncertainty. The lever arm's length must be measured from the centerline of the dynamometer to the point at which the reference force is measured. The lever arm must be perpendicular to gravity (i.e., horizontal), and it must be perpendicular to the dynamometer's rotational axis. Balance the lever arm's torque or quantify its net hanging torque, NIST-traceable within ±1% uncertainty, and account for it as part of the reference torque.

(c) Recommended procedure to quantify reference force. We recommend dead-weight calibration, but you may use either of the following procedures to quantify the reference force, NIST-traceable within ±0.5% uncertainty.

(1) Dead-weight calibration. This technique applies a known force by hanging known weights at a known distance along a lever arm. Make sure the weights' lever arm is perpendicular to gravity (i.e., horizontal) and perpendicular to the dynamometer's rotational axis. Apply at least six calibration-weight combinations for each applicable torque-measuring range, spacing the weight quantities about equally over the range. Oscillate or rotate the dynamometer during calibration to reduce frictional static hysteresis. Determine each weight's reference force by multiplying its NIST-traceable mass by the local acceleration of Earth's gravity, as described in § 1065.630. Calculate the reference torque as the weights' reference force multiplied by the lever arm reference length.

(2) Strain gage, load transducer, or proving ring calibration. This technique applies force either by hanging weights on a lever arm (these weights and their lever arm length are not used as part of the reference torque determination) or by operating the dynamometer at different torques. Apply at least six force combinations for each applicable torque-measuring range, spacing the force quantities about equally over the range. Oscillate or rotate the dynamometer during calibration to reduce frictional static hysteresis. In this case, the reference torque is determined by multiplying the force output from the reference meter (such as a strain gage, load transducer, or proving ring) by its effective lever-arm length, which you measure from the point where the force measurement is made to the dynamometer's rotational axis. Make sure you measure this length perpendicular to the reference meter's measurement axis and perpendicular to the dynamometer's rotational axis.

(a) Calibrate instruments for measuring pressure, temperature, and dewpoint upon initial installation. Follow the instrument manufacturer's instructions and use good engineering judgment to repeat the calibration, as follows:

(1) Pressure. We recommend temperature-compensated, digital-pneumatic, or deadweight pressure calibrators, with data-logging capabilities to minimize transcription errors. We recommend using calibration reference quantities that are NIST-traceable within ±0.5% uncertainty.

(2) Temperature. We recommend digital dry-block or stirred-liquid temperature calibrators, with data logging capabilities to minimize transcription errors. We recommend using calibration reference quantities that are NIST-traceable within ±0.5% uncertainty. You may perform linearity verification for temperature measurement systems with thermocouples, RTDs, and thermistors by removing the sensor from the system and using a simulator in its place. Use a NIST-traceable simulator that is independently calibrated and, as appropriate, cold-junction compensated. The simulator uncertainty scaled to absolute temperature must be less than 0.5% of Tmax. If you use this option, you must use sensors that the supplier states are accurate to better than 0.5% of Tmax compared with their standard calibration curve.

(3) Dewpoint. We recommend a minimum of three different temperature-equilibrated and temperature-monitored calibration salt solutions in containers that seal completely around the dewpoint sensor. We recommend using calibration reference quantities that are NIST-traceable within ±0.5% uncertainty.

(b) You may remove system components for off-site calibration. We recommend specifying calibration reference quantities that are NIST-traceable within ±0.5% uncertainty.

(a) This subpart describes required and recommended calibrations and verifications of measurement systems. See subpart C of this part for specifications that apply to individual instruments.

(b) You must generally use complete measurement systems when performing calibrations or verifications in this subpart. For example, this would generally involve evaluating instruments based on values recorded with the complete system you use for recording test data, including analog-to-digital converters. For some calibrations and verifications, we may specify that you disconnect part of the measurement system to introduce a simulated signal.

(c) If we do not specify a calibration or verification for a portion of a measurement system, calibrate that portion of your system and verify its performance at a frequency consistent with any recommendations from the measurement-system manufacturer, consistent with good engineering judgment.

(d) Use NIST-traceable standards to the tolerances we specify for calibrations and verifications. Where we specify the need to use NIST-traceable standards, you may alternatively use international standards recognized by the CIPM Mutual Recognition Arrangement that are not NIST-traceable.

The following table summarizes the required and recommended calibrations and verifications described in this subpart and indicates when these have to be performed:

(a) This section describes how to determine the accuracy, repeatability, and noise of an instrument. Table 1 of § 1065.205 specifies recommended values for individual instruments.

(b) We do not require you to verify instrument accuracy, repeatability, or noise.

However, it may be useful to consider these verifications to define a specification for a new instrument, to verify the performance of a new instrument upon delivery, or to troubleshoot an existing instrument.

(c) In this section we use the letter “y” to denote a generic measured quantity, the superscript over-bar to denote an arithmetic mean (such as y ), and the subscript “ref” to denote the reference quantity being measured.

(d) Conduct these verifications as follows:

(1) Prepare an instrument so it operates at its specified temperatures, pressures, and flows. Perform any instrument linearization or calibration procedures prescribed by the instrument manufacturer.

(2) Zero the instrument as you would before an emission test by introducing a zero signal. Depending on the instrument, this may be a zero-concentration gas, a reference signal, a set of reference thermodynamic conditions, or some combination of these. For gas analyzers, use a zero gas that meets the specifications of § 1065.750.

(3) Span the instrument as you would before an emission test by introducing a span signal. Depending on the instrument, this may be a span-concentration gas, a reference signal, a set of reference thermodynamic conditions, or some combination of these. For gas analyzers, use a span gas that meets the specifications of § 1065.750.

(4) Use the instrument to quantify a NIST-traceable reference quantity, yref. For gas analyzers the reference gas must meet the specifications of § 1065.750. Select a reference quantity near the mean value expected during testing. For all gas analyzers, use a quantity near the flow-weighted mean concentration expected at the standard or expected during testing, whichever is greater. For noise verification, use the same zero gas from paragraph (d)(2) of this section as the reference quantity. In all cases, allow time for the instrument to stabilize while it measures the reference quantity. Stabilization time may include time to purge an instrument and time to account for its response.

(5) Sample and record values for 30 seconds (you may select a longer sampling period if the recording update frequency is less than 0.5 Hz), record the arithmetic mean, y i and record the standard deviation, σi of the recorded values. Refer to § 1065.602 for an example of calculating arithmetic mean and standard deviation.

(6) Also, if the reference quantity is not absolutely constant, which might be the case with a reference flow, sample and record values of yrefi for 30 seconds and record the arithmetic mean of the values, y ref. Refer to § 1065.602 for an example of calculating arithmetic mean.

(7) Subtract the reference value, yref (or y refi), from the arithmetic mean, y i. Record this value as the error, εi.

(8) Repeat the steps specified in paragraphs (d)(2) through (7) of this section until you have ten arithmetic means (y 1, y 2, y i, ...y 10), ten standard deviations, (σ1, σ2, σi,...σ10), and ten errors (ε1, ε2, εi,...ε10).

(9) Use the following values to quantify your measurements:

(i) Accuracy. Instrument accuracy is the absolute difference between the reference quantity, yref (or y ref), and the arithmetic mean of the ten y i, y values. Refer to the example of an accuracy calculation in § 1065.602. We recommend that instrument accuracy be within the specifications in Table 1 of § 1065.205.

(ii) Repeatability. Repeatability is two times the standard deviation of the ten errors (that is, repeatability = 2 · sε). Refer to the example of a standard-deviation calculation in § 1065.602. We recommend that instrument repeatability be within the specifications in Table 1 of § 1065.205.

(iii) Noise. Noise is two times the root-mean-square of the ten standard deviations (that is, noise = 2 · rmsσ) when the reference signal is a zero-quantity signal. Refer to the example of a root-mean-square calculation in § 1065.602. We recommend that instrument noise be within the specifications in Table 1 of § 1065.205.

(10) You may use a measurement instrument that does not meet the accuracy, repeatability, or noise specifications in Table 1 of § 1065.205, as long as you meet the following criteria:

(i) Your measurement systems meet all the other required calibration, verification, and validation specifications that apply as specified in the regulations.

(ii) The measurement deficiency does not adversely affect your ability to demonstrate compliance with the applicable standards in this chapter.

(a) Scope and frequency. Perform linearity verification on each measurement system listed in Table 1 of this section at least as frequently as indicated in Table 1 of § 1065.303, consistent with measurement system manufacturer's recommendations and good engineering judgment. The intent of linearity verification is to determine that a measurement system responds accurately and proportionally over the measurement range of interest. Linearity verification generally consists of introducing a series of at least 10 reference values to a measurement system. The measurement system quantifies each reference value. The measured values are then collectively compared to the reference values by using a least-squares linear regression and the linearity criteria specified in Table 1 of this section.

(b) Performance requirements. If a measurement system does not meet the applicable linearity criteria referenced in Table 1 of this section, correct the deficiency by re-calibrating, servicing, or replacing components as needed. Repeat the linearity verification after correcting the deficiency to ensure that the measurement system meets the linearity criteria. Before you may use a measurement system that does not meet linearity criteria, you must demonstrate to us that the deficiency does not adversely affect your ability to demonstrate compliance with the applicable standards in this chapter.

(c) Procedure. Use the following linearity verification protocol, or use good engineering judgment to develop a different protocol that satisfies the intent of this section, as described in paragraph (a) of this section:

(1) In this paragraph (c), the letter “y” denotes a generic measured quantity, the superscript over-bar denotes an arithmetic mean (such as y ), and the subscript “ref” denotes the known or reference quantity being measured.

(2) Use good engineering judgment to operate a measurement system at normal operating conditions. This may include any specified adjustment or periodic calibration of the measurement system.

(3) If applicable, zero the instrument as you would before an emission test by introducing a zero signal. Depending on the instrument, this may be a zero-concentration gas, a reference signal, a set of reference thermodynamic conditions, or some combination of these. For gas analyzers, use a zero gas that meets the specifications of § 1065.750 and introduce it directly at the analyzer port.

(4) If applicable, span the instrument as you would before an emission test by introducing a span signal. Depending on the instrument, this may be a span-concentration gas, a reference signal, a set of reference thermodynamic conditions, or some combination of these. For gas analyzers, use a span gas that meets the specifications of § 1065.750 and introduce it directly at the analyzer port.

(5) If applicable, after spanning the instrument, check zero with the same signal you used in paragraph (c)(3) of this section. Based on the zero reading, use good engineering judgment to determine whether or not to rezero and or re-span the instrument before continuing.

(6) For all measured quantities, use the instrument manufacturer's recommendations and good engineering judgment to select reference values, yrefi, that cover a range of values that you expect would prevent extrapolation beyond these values during emission testing. We recommend selecting a zero reference signal as one of the reference values for the linearity verification. For pressure, temperature, dewpoint, power, current, voltage, photoacoustic analyzers, and GC-ECD linearity verifications, we recommend at least three reference values. For all other linearity verifications select at least ten reference values.

(7) Use the instrument manufacturer's recommendations and good engineering judgment to select the order in which you will introduce the series of reference values. For example, you may select the reference values randomly to avoid correlation with previous measurements and to avoid hysteresis; you may select reference values in ascending or descending order to avoid long settling times of reference signals; or you may select values to ascend and then descend to incorporate the effects of any instrument hysteresis into the linearity verification.

(8) Generate reference quantities as described in paragraph (d) of this section. For gas analyzers, use gas concentrations known to be within the specifications of § 1065.750 and introduce them directly at the analyzer port.

(9) Introduce a reference signal to the measurement instrument.

(10) Allow time for the instrument to stabilize while it measures the value at the reference condition. Stabilization time may include time to purge an instrument and time to account for its response.

(11) At a recording frequency of at least f Hz, specified in Table 1 of § 1065.205, measure the value at the reference condition for 30 seconds (you may select a longer sampling period if the recording update frequency is less than 0.5 Hz) and record the arithmetic mean of the recorded values, y i. Refer to § 1065.602 for an example of calculating an arithmetic mean.

(12) Repeat the steps in paragraphs (c)(9) though (11) of this section until measurements are complete at each of the reference conditions.

(13) Use the arithmetic means, y i, and reference values, yrefi, to calculate least-squares linear regression parameters and statistical values to compare to the minimum performance criteria specified in Table 1 of this section. Use the calculations for a floating intercept described in § 1065.602. Using good engineering judgment, you may weight the results of individual data pairs (i.e., (yrefi, y i)), in the linear regression calculations.

(d) Reference signals. This paragraph (d) describes recommended methods for generating reference values for the linearity-verification protocol in paragraph (c) of this section. Use reference values that simulate actual values, or introduce an actual value and measure it with a reference-measurement system. In the latter case, the reference value is the value reported by the reference-measurement system. Reference values and reference-measurement systems must be NIST-traceable. We recommend using calibration reference quantities that are NIST-traceable within ±0.5% uncertainty, if not specified elsewhere in this part 1065. Use the following recommended methods to generate reference values or use good engineering judgment to select a different reference:

(1) Speed. Run the engine or dynamometer at a series of steady-state speeds and use a strobe, photo tachometer, or laser tachometer to record reference speeds.

(2) Torque. Use a series of calibration weights and a calibration lever arm to simulate engine torque. You may instead use the engine or dynamometer itself to generate a nominal torque that is measured by a reference load cell or proving ring in series with the torque-measurement system. In this case, use the reference load cell measurement as the reference value. Refer to § 1065.310 for a torque-calibration procedure similar to the linearity verification in this section.

(3) Electrical power, current, and voltage. You must perform linearity verification for either electrical power meters, or for current and voltage meters. Perform linearity verifications using a reference meter and controlled sources of current and voltage. We recommend using a complete calibration system that is suitable for the electrical power distribution industry.

(4) Fuel and DEF mass flow rate. Use a gravimetric reference measurement (such as a scale, balance, or mass comparator) and a container. Use a stopwatch or timer to measure the time intervals over which reference masses of fluid pass through the mass flow rate meter. Use good engineering judgment to correct the reference mass flowing through the mass flow rate meter for buoyancy effects from any tubes, temperature probes, or objects submerged in the fluid in the container that are not attached to the container. If the container has any tubes or wires connected to the container, recalibrate the gravimetric reference measurement device with them connected and at normal operating pressure using calibration weights that meet the requirements in § 1065.790. The corrected reference mass that flowed through the mass flow rate meter during a time interval divided by the duration of the time interval is the average reference mass flow rate. For meters that report a different quantity (such as actual volume, standard volume, or moles), convert the reported quantity to mass. For meters that report a cumulative quantity calculate the average measured mass flow rate as the difference in the reported cumulative mass during the time interval divided by the duration of the time interval. For measuring flow rate of gaseous fuel prevent condensation on the fuel container and any attached tubes, fittings, or regulators.

(5) Flow rates—inlet air, dilution air, diluted exhaust, raw exhaust, or sample flow. Use a reference flow meter with a blower or pump to simulate flow rates. Use a restrictor, diverter valve, a variable-speed blower or a variable-speed pump to control the range of flow rates. Use the reference meter's response as the reference values.

(i) Reference flow meters. Because the flow range requirements for these various flows are large, we allow a variety of reference meters. For example, for diluted exhaust flow for a full-flow dilution system, we recommend a reference subsonic venturi flow meter with a restrictor valve and a blower to simulate flow rates. For inlet air, dilution air, diluted exhaust for partial-flow dilution, raw exhaust, or sample flow, we allow reference meters such as critical flow orifices, critical flow venturis, laminar flow elements, master mass flow standards, or Roots meters. Make sure the reference meter is calibrated and its calibration is NIST-traceable. If you use the difference of two flow measurements to determine a net flow rate, you may use one of the measurements as a reference for the other.

(ii) Reference flow values. Because the reference flow is not absolutely constant, sample and record values of n refi for 30 seconds and use the arithmetic mean of the values, n ref, as the reference value. Refer to § 1065.602 for an example of calculating arithmetic mean.

(6) Gas division. Use one of the two reference signals:

(i) At the outlet of the gas-division system, connect a gas analyzer that meets the linearity verification described in this section and has not been linearized with the gas divider being verified. For example, verify the linearity of an analyzer using a series of reference analytical gases directly from compressed gas cylinders that meet the specifications of § 1065.750. We recommend using a FID analyzer or a PMD or MPD O2 analyzer because of their inherent linearity. Operate this analyzer consistent with how you would operate it during an emission test. Connect a span gas containing only a single constituent of interest with balance of purified air or purified N2 to the gas-divider inlet. Use the gas-division system to divide the span gas with purified air or nitrogen. Select gas divisions that you typically use. Use a selected gas division as the measured value. Use the analyzer response divided by the span gas concentration as the reference gas-division value. Because the instrument response is not absolutely constant, sample and record values of xrefi for 30 seconds and use the arithmetic mean of the values, x ref, as the reference value. Refer to § 1065.602 for an example of calculating arithmetic mean.

(ii) Using good engineering judgment and the gas divider manufacturer's recommendations, use one or more reference flow meters to measure the flow rates of the gas divider and verify the gas-division value.

(7) Continuous constituent concentration. For reference values, use a series of gas cylinders of known gas concentration containing only a single constituent of interest with balance of purified air or purified N2 or use a gas-division system that is known to be linear with a span gas. Gas cylinders, gas-division systems, and span gases that you use for reference values must meet the specifications of § 1065.750.

(8) Temperature. You may perform the linearity verification for temperature measurement systems with thermocouples, RTDs, and thermistors by removing the sensor from the system and using a simulator in its place. Use a NIST-traceable simulator that is independently calibrated and, as appropriate, cold-junction-compensated. The simulator uncertainty scaled to absolute temperature must be less than 0.5% of Tmax. If you use this option, you must use sensors that the supplier states are accurate to better than 0.5% of Tmax compared with their standard calibration curve.

(9) Mass. For linearity verification for gravimetric PM balances, fuel mass scales, and DEF mass scales, use external calibration weights that meet the requirements in § 1065.790. Perform the linearity verification for fuel mass scales and DEF mass scales with the in-use container, installing all objects that interface with the container. For example, this includes all tubes, temperature probes, and objects submerged in the fluid in the container; it also includes tubes, fittings, regulators, and wires, and any other objects attached to the container. We recommend that you develop and apply appropriate buoyancy corrections for the configuration of your mass scale during normal testing, consistent with good engineering judgment. Account for the scale weighing a calibration weight instead of fluid if you calculate buoyancy corrections. You may also correct for the effect of natural convection currents from temperature differences between the container and ambient air. Prepare for linearity verification by taking the following steps for vented and unvented containers:

(i) If the container is vented to ambient, fill the container and tubes with fluid above the minimum level used to trigger a fill operation; drain the fluid down to the minimum level; tare the scale; and perform the linearity verification.

(ii) If the container is rigid and not vented, drain the fluid down to the minimum level; fill all tubes attached to the container to normal operating pressure; tare the scale; and perform the linearity verification.

(e) Measurement systems that require linearity verification. Table 1 of this section indicates measurement systems that require linearity verification, subject to the following provisions:

(1) Perform linearity verification more frequently based on the instrument manufacturer's recommendation or good engineering judgment.

(2) The expression “xmin” refers to the reference value used during linearity verification that is closest to zero. This is the value used to calculate the first tolerance in Table 1 of this section using the intercept, a0. Note that this value may be zero, positive, or negative depending on the reference values. For example, if the reference values chosen to validate a pressure transducer vary from −10 to −1 kPa, xmin is −1 kPa. If the reference values used to validate a temperature device vary from 290 to 390 K, xmin is 290 K.

(3) The expression “max” generally refers to the absolute value of the reference value used during linearity verification that is furthest from zero. This is the value used to scale the first and third tolerances in Table 1 of this section using a0 and SEE. For example, if the reference values chosen to validate a pressure transducer vary from −10 to −1 kPa, then pmax is +10 kPa. If the reference values used to validate a temperature device vary from 290 to 390 K, then Tmax is 390 K. For gas dividers where “max” is expressed as, xmax/xspan; xmax is the maximum gas concentration used during the verification, xspan is the undivided, undiluted, span gas concentration, and the resulting ratio is the maximum divider point reference value used during the verification (typically 1). The following are special cases where “max” refers to a different value:

(i) For linearity verification of a PM balance, mmax is the typical mass of a PM filter.

(ii) For linearity verification of a torque measurement system used with the engine's primary output shaft, Tmax is the manufacturer's specified peak torque of the lowest torque engine expected during testing.

(iii) For linearity verification of a fuel mass scale, mmax is determined based on the range of engines and test interval durations expected during testing. It is the minimum, over all engines expected during testing, of the fuel consumption expected over the minimum test interval duration at the engine's maximum fuel rate. If the minimum test interval duration used during testing does not change with engine power or if the minimum test interval duration used during testing increases with engine power, mmax is given by Eq. 1065.307-1. Calculate mmax using the following equation:

(iv) For linearity verification of a DEF mass scale, mmax is 10% of the value determined for a fuel mass scale in paragraph (e)(3)(iii) of this section. You may determine mmax for a DEF mass scale by evaluating mmax for a fuel mass scale based only on the DEF-using engines expected during testing.

(v) For linearity verification of a fuel flow rate meter, m max is the manufacturer's specified maximum fuel rate of the lowest-power engine expected during testing.

(vi) For linearity verification of a DEF flow rate meter, m max is 10% of the manufacturer's specified maximum fuel rate of the lowest-power DEF-using engine expected during testing.

(vii) For linearity verification of an intake-air flow rate meter, n max is the manufacturer's specified maximum intake-air flow rate (converted to molar flow rate) of the lowest-power engine expected during testing.

(viii) For linearity verification of a raw exhaust flow rate meter, n max is the manufacturer's specified maximum exhaust flow rate (converted to molar flow rate) of the lowest-power engine expected during testing.

(ix) For linearity verification of an electrical-power measurement system used to determine the engine's primary output shaft torque, Pmax is the manufacturer's specified maximum power of the lowest-power engine expected during testing.

(x) For linearity verification of an electrical-current measurement system used to determine the engine's primary output shaft torque, Imax is the maximum current expected on the lowest-power engine expected during testing.

(xi) For linearity verification of an electrical-voltage measurement system used to determine the engine's primary output shaft torque, Vmax is the minimum peak voltage expected on the range of engines expected during testing.

(4) The specified ranges are inclusive. For example, a specified range of 0.98-1.02 for a1 means 0.98≤a1≤1.02.

(5) Table 2 of this section describes optional verification procedures you may perform instead of linearity verification for certain systems. The following provisions apply for the alternative verification procedures:

(i) Perform the propane check verification described in § 1065.341 at the frequency specified in Table 1 of § 1065.303.

(ii) Perform the carbon balance error verification described in § 1065.543 on all test sequences that use the corresponding system. It must also meet the restrictions listed in Table 2 of this section. You may evaluate the carbon balance error verification multiple ways with different inputs to validate multiple flow-measurement systems.

(6) You must meet the a1 criteria for these quantities only if the absolute value of the quantity is required, as opposed to a signal that is only linearly proportional to the actual value.

(7) Linearity verification is required for the following temperature measurements:

(i) The following temperature measurements always require linearity verification:

(A) Air intake.

(B) Aftertreatment bed(s), for engines tested with aftertreatment devices subject to cold-start testing.

(C) Dilution air for gaseous and PM sampling, including CVS, double-dilution, and partial-flow systems.

(D) PM sample.

(E) Chiller sample, for gaseous sampling systems that use thermal chillers to dry samples and use chiller temperature to calculate the dewpoint at the outlet of the chiller. For your testing, if you choose to use a high alarm temperature setpoint for the chiller temperature as a constant value in determining the amount of water removed from the emission sample, you may use good engineering judgment to verify the accuracy of the high alarm temperature setpoint instead of linearity verification on the chiller temperature. To verify that the alarm trip point value is no less than 2.0 °C below the reference value at the trip point, we recommend that you input a reference simulated temperature signal below the alarm trip point and increase this signal until the high alarm trips.

(F) Transmission oil.

(G) Axle gear oil.

(ii) Linearity verification is required for the following temperature measurements if these temperature measurements are specified by the engine manufacturer:

(A) Fuel inlet.

(B) Air outlet to the test cell's charge air cooler air outlet, for engines tested with a laboratory heat exchanger that simulates an installed charge air cooler.

(C) Coolant inlet to the test cell's charge air cooler, for engines tested with a laboratory heat exchanger that simulates an installed charge air cooler.

(D) Oil in the sump/pan.

(E) Coolant before the thermostat, for liquid-cooled engines.

(8) Linearity verification is required for the following pressure measurements:

(i) The following pressure measurements always require linearity verification:

(A) Air intake restriction.

(B) Exhaust back pressure as required in § 1065.130(h).

(C) Barometer.

(D) CVS inlet gage pressure where the raw exhaust enters the tunnel.

(E) Sample dryer, for gaseous sampling systems that use either osmotic-membrane or thermal chillers to dry samples. For your testing, if you choose to use a low alarm pressure setpoint for the sample dryer pressure as a constant value in determining the amount of water removed from the emission sample, you may use good engineering judgment to verify the accuracy of the low alarm pressure setpoint instead of linearity verification on the sample dryer pressure. To verify that the trip point value is no more than 4.0 kPa above the reference value at the trip point, we recommend that you input a reference pressure signal above the alarm trip point and decrease this signal until the low alarm trips.

(ii) Linearity verification is required for the following pressure measurements if these pressure measurements are specified by the engine manufacturer:

(A) The test cell's charge air cooler and interconnecting pipe pressure drop, for turbo-charged engines tested with a laboratory heat exchanger that simulates an installed charge air cooler.

(B) Fuel outlet.

(f) Performance criteria for measurement systems. Table 1 follows:

(g) Alternative verification procedures. Table 2 follows:

(a) Scope and frequency. This section describes a verification procedure for system response and updating-recording frequency for continuous gas analyzers that output a gas species mole fraction (i.e., concentration) using a single gas detector, i.e., gas analyzers not continuously compensated for other gas species measured with multiple gas detectors. See § 1065.309 for verification procedures that apply to continuous gas analyzers that are continuously compensated for other gas species measured with multiple gas detectors. Perform this verification to determine the system response of the continuous gas analyzer and its sampling system. This verification is required for continuous gas analyzers used for transient or ramped-modal testing. You need not perform this verification for batch gas analyzer systems or for continuous gas analyzer systems that are used only for discrete-mode testing. Perform this verification after initial installation (i.e., test cell commissioning) and after any modifications to the system that would change system response. For example, perform this verification if you add a significant volume to the transfer lines by increasing their length or adding a filter; or if you reduce the frequency at which the gas analyzer updates its output or the frequency at which you sample and record gas-analyzer concentrations.

(b) Measurement principles. This test verifies that the updating and recording frequencies match the overall system response to a rapid change in the value of concentrations at the sample probe. Gas analyzers and their sampling systems must be optimized such that their overall response to a rapid change in concentration is updated and recorded at an appropriate frequency to prevent loss of information. This test also verifies that the measurement system meets a minimum response time. You may use the results of this test to determine transformation time, t50, for the purposes of time alignment of continuous data in accordance with § 1065.650(c)(2)(i). You may also use an alternate procedure to determine t50 in accordance with good engineering judgment. Note that any such procedure for determining t50 must account for both transport delay and analyzer response time.

(c) System requirements. Demonstrate that each continuous analyzer has adequate update and recording frequencies and has a minimum rise time and a minimum fall time during a rapid change in gas concentration. You must meet one of the following criteria:

(1) The product of the mean rise time, t10-90, and the frequency at which the system records an updated concentration must be at least 5, and the product of the mean fall time, t90-10, and the frequency at which the system records an updated concentration must be at least 5. If the recording frequency is different than the analyzer's output update frequency, you must use the lower of these two frequencies for this verification, which is referred to as the updating-recording frequency. This verification applies to the nominal updating and recording frequencies. This criterion makes no assumption regarding the frequency content of changes in emission concentrations during emission testing; therefore, it is valid for any testing. Also, the mean rise time must be at or below 10 seconds and the mean fall time must be at or below 10 seconds.

(2) The frequency at which the system records an updated concentration must be at least 5 Hz. This criterion assumes that the frequency content of significant changes in emission concentrations during emission testing do not exceed 1 Hz. Also, the mean rise time must be at or below 10 seconds and the mean fall time must be at or below 10 seconds.

(3) You may use other criteria if we approve the criteria in advance.

(4) You may meet the overall PEMS verification in § 1065.920 instead of the verification in this section for field testing with PEMS.

(d) Procedure. Use the following procedure to verify the response of each continuous gas analyzer:

(1) Instrument setup. Follow the analyzer manufacturer's start-up and operating instructions. Adjust the measurement system as needed to optimize performance. Run this verification with the analyzer operating in the same manner you will use for emission testing. If the analyzer shares its sampling system with other analyzers, and if gas flow to the other analyzers will affect the system response time, then start up and operate the other analyzers while running this verification test. You may run this verification test on multiple analyzers sharing the same sampling system at the same time. If you use any analog or real-time digital filters during emission testing, you must operate those filters in the same manner during this verification.

(2) Equipment setup. We recommend using minimal lengths of gas transfer lines between all connections and fast-acting three-way valves (2 inlets, 1 outlet) to control the flow of zero and blended span gases to the sample system's probe inlet or a tee near the outlet of the probe. If you inject the gas at a tee near the outlet of the probe, you may correct the transformation time, t50, for an estimate of the transport time from the probe inlet to the tee. Normally the gas flow rate is higher than the sample flow rate and the excess is overflowed out the inlet of the probe. If the gas flow rate is lower than the sample flow rate, the gas concentrations must be adjusted to account for the dilution from ambient air drawn into the probe. We recommend you use the final, stabilized analyzer reading as the final gas concentration. Select span gases for the species being measured. You may use binary or multi-gas span gases. You may use a gas blending or mixing device to blend span gases. A gas blending or mixing device is recommended when blending span gases diluted in N2 with span gases diluted in air. You may use a multi-gas span gas, such as NO-CO-CO2-C3H8-CH4, to verify multiple analyzers at the same time. If you use standard binary span gases, you must run separate response tests for each analyzer. In designing your experimental setup, avoid pressure pulsations due to stopping the flow through the gas-blending device. The change in gas concentration must be at least 20% of the analyzer's range.

(3) Data collection. (i) Start the flow of zero gas.

(ii) Allow for stabilization, accounting for transport delays and the slowest analyzer's full response.

(iii) Start recording data. For this verification you must record data at a frequency greater than or equal to that of the updating-recording frequency used during emission testing. You may not use interpolation or filtering to alter the recorded values.

(iv) Switch the flow to allow the blended span gases to flow to the analyzer. If you intend to use the data from this test to determine t50 for time alignment, record this time as t0.

(v) Allow for transport delays and the slowest analyzer's full response.

(vi) Switch the flow to allow zero gas to flow to the analyzer. If you intend to use the data from this test to determine t50 for time alignment, record this time as t100.

(vii) Allow for transport delays and the slowest analyzer's full response.

(viii) Repeat the steps in paragraphs (d)(3)(iv) through (vii) of this section to record seven full cycles, ending with zero gas flowing to the analyzers.

(ix) Stop recording.

(e) Performance evaluation. (1) If you choose to demonstrate compliance with paragraph (c)(1) of this section, use the data from paragraph (d)(3) of this section to calculate the mean rise time, t10-90, and mean fall time, t90-10, for each of the analyzers being verified. You may use interpolation between recorded values to determine rise and fall times. If the recording frequency used during emission testing is different from the analyzer's output update frequency, you must use the lower of these two frequencies for this verification. Multiply these times (in seconds) by their respective updating-recording frequencies in Hertz (1/second). The resulting product must be at least 5 for both rise time and fall time. If either value is less than 5, increase the updating-recording frequency, or adjust the flows or design of the sampling system to increase the rise time and fall time as needed. You may also configure analog or digital filters before recording to increase rise and fall times. In no case may the mean rise time or mean fall time be greater than 10 seconds.

(2) If a measurement system fails the criterion in paragraph (e)(1) of this section, ensure that signals from the system are updated and recorded at a frequency of at least 5 Hz. In no case may the mean rise time or mean fall time be greater than 10 seconds.

(3) If a measurement system fails the criteria in paragraphs (e)(1) and (2) of this section, you may use the measurement system only if the deficiency does not adversely affect your ability to show compliance with the applicable standards in this chapter.

(f) Transformation time, t50, determination. If you choose to determine t50 for purposes of time alignment using data generated in paragraph (d)(3) of this section, calculate the mean t0-50 and the mean t100-50 from the recorded data. Average these two values to determine the final t50 for the purposes of time alignment in accordance with § 1065.650(c)(2)(i).

(g) Optional procedure. Instead of using a three-way valve to switch between zero and span gases, you may use a fast-acting two-way valve to switch sampling between ambient air and span gas at the probe inlet. For this alternate procedure, the following provisions apply:

(1) If your probe is sampling from a continuously flowing gas stream (e.g., a CVS tunnel), you may adjust the span gas flow rate to be different than the sample flow rate.

(2) If your probe is sampling from a gas stream that is not continuously flowing (e.g., a raw exhaust stack), you must adjust the span gas flow rate to be less than the sample flow rate so ambient air is always being drawn into the probe inlet. This avoids errors associated with overflowing span gas out of the probe inlet and drawing it back in when sampling ambient air.

(3) When sampling ambient air or ambient air mixed with span gas, all the analyzer readings must be stable within ±0.5% of the target gas concentration step size. If any analyzer reading is outside the specified range, you must resolve the problem and verify that all the analyzer readings meet this specification.

(4) For oxygen analyzers, you may use purified N2 as the zero gas and ambient air (plus purified N2 if needed) as the reference gas. Perform the verification with seven repeat measurements that each consist of stabilizing with purified N2, switching to ambient air and observing the analyzer's rise and stabilized reading, followed by switching back to purified N2 and observing the analyzer's fall and stabilized reading.

(a) Scope and frequency. This section describes a verification procedure for system response and updating-recording frequency for continuous gas analyzers that output a single gas species mole fraction (i.e., concentration) based on a continuous combination of multiple gas species measured with multiple detectors (i.e., gas analyzers continuously compensated for other gas species). See § 1065.308 for verification procedures that apply to continuous gas analyzers that are not continuously compensated for other gas species or that use only one detector for gaseous species. Perform this verification to determine the system response of the continuous gas analyzer and its sampling system. This verification is required for continuous gas analyzers used for transient or ramped-modal testing. You need not perform this verification for batch gas analyzers or for continuous gas analyzers that are used only for discrete-mode testing. For this check we consider water vapor a gaseous constituent. This verification does not apply to any processing of individual analyzer signals that are time-aligned to their t50 times and were verified according to § 1065.308. For example, this verification does not apply to correction for water removed from the sample done in post-processing according to § 1065.659 (40 CFR 1066.620 for vehicle testing) and it does not apply to NMHC determination from THC and CH4 according to § 1065.660. Perform this verification after initial installation (i.e., test cell commissioning) and after any modifications to the system that would change the system response.

(b) Measurement principles. This procedure verifies that the updating and recording frequencies match the overall system response to a rapid change in the value of concentrations at the sample probe. It indirectly verifies the time-alignment and uniform response of all the continuous gas detectors used to generate a continuously combined/compensated concentration measurement signal. Gas analyzer systems must be optimized such that their overall response to rapid change in concentration is updated and recorded at an appropriate frequency to prevent loss of information. This test also verifies that the measurement system meets a minimum response time. For this procedure, ensure that all compensation algorithms and humidity corrections are turned on. You may use the results of this test to determine transformation time, t50, for the purposes of time alignment of continuous data in accordance with § 1065.650(c)(2)(i). You may also use an alternate procedure to determine t50 consistent with good engineering judgment. Note that any such procedure for determining t50 must account for both transport delay and analyzer response time.

(c) System requirements. Demonstrate that each continuously combined/compensated concentration measurement has adequate updating and recording frequencies and has a minimum rise time and a minimum fall time during a system response to a rapid change in multiple gas concentrations, including H2O concentration if H2O compensation is applied. You must meet one of the following criteria:

(1) The product of the mean rise time, t10-90, and the frequency at which the system records an updated concentration must be at least 5, and the product of the mean fall time, t90-10, and the frequency at which the system records an updated concentration must be at least 5. If the recording frequency is different than the update frequency of the continuously combined/compensated signal, you must use the lower of these two frequencies for this verification. This criterion makes no assumption regarding the frequency content of changes in emission concentrations during emission testing; therefore, it is valid for any testing. Also, the mean rise time must be at or below 10 seconds and the mean fall time must be at or below 10 seconds.

(2) The frequency at which the system records an updated concentration must be at least 5 Hz. This criterion assumes that the frequency content of significant changes in emission concentrations during emission testing do not exceed 1 Hz. Also, the mean rise time must be at or below 10 seconds and the mean fall time must be at or below 10 seconds.

(3) You may use other criteria if we approve them in advance.

(4) You may meet the overall PEMS verification in § 1065.920 instead of the verification in this section for field testing with PEMS.

(d) Procedure. Use the following procedure to verify the response of each continuously compensated analyzer (verify the combined signal, not each individual continuously combined concentration signal):

(1) Instrument setup. Follow the analyzer manufacturer's start-up and operating instructions. Adjust the measurement system as needed to optimize performance. Run this verification with the analyzer operating in the same manner you will use for emission testing. If the analyzer shares its sampling system with other analyzers, and if gas flow to the other analyzers will affect the system response time, then start up and operate the other analyzers while running this verification test. You may run this verification test on multiple analyzers sharing the same sampling system at the same time. If you use any analog or real-time digital filters during emission testing, you must operate those filters in the same manner during this verification.

(2) Equipment setup. We recommend using minimal lengths of gas transfer lines between all connections and fast-acting three-way valves (2 inlets, 1 outlet) to control the flow of zero and blended span gases to the sample system's probe inlet or a tee near the outlet of the probe. If you inject the gas at a tee near the outlet of the probe, you may correct the transformation time, t50, for an estimate of the transport time from the probe inlet to the tee. Normally the gas flow rate is higher than the sample flow rate and the excess is overflowed out the inlet of the probe. If the gas flow rate is lower than the sample flow rate, the gas concentrations must be adjusted to account for the dilution from ambient air drawn into the probe. We recommend you use the final, stabilized analyzer reading as the final gas concentration. Select span gases for the species being continuously combined, other than H2O. Select concentrations of compensating species that will yield concentrations of these species at the analyzer inlet that covers the range of concentrations expected during testing. You may use binary or multi-gas span gases. You may use a gas blending or mixing device to blend span gases. A gas blending or mixing device is recommended when blending span gases diluted in N2 with span gases diluted in air. You may use a multi-gas span gas, such as NO-CO-CO2-C3H8-CH4, to verify multiple analyzers at the same time. In designing your experimental setup, avoid pressure pulsations due to stopping the flow through the gas blending device. The change in gas concentration must be at least 20% of the analyzer's range. If H2O correction is applicable, then span gases must be humidified before entering the analyzer; however, you may not humidify NO2 span gas by passing it through a sealed humidification vessel that contains H2O. You must humidify NO2 span gas with another moist gas stream. We recommend humidifying your NO-CO-CO2-C3H8-CH4, balance N2, blended gas by bubbling the gas mixture that meets the specifications in § 1065.750 through distilled H2O in a sealed vessel and then mixing the gas with dry NO2 gas, balance purified air, or by using a device that introduces distilled H2O as vapor into a controlled span gas flow. If the sample does not pass through a dryer during emission testing, humidify your span gas to an H2O level at or above the maximum expected during emission testing. If the sample passes through a dryer during emission testing, it must pass the sample dryer verification check in § 1065.342, and you must humidify your span gas to an H2O level at or above the level determined in § 1065.145(e)(2) for that dryer. If you are humidifying span gases without NO2, use good engineering judgment to ensure that the wall temperatures in the transfer lines, fittings, and valves from the humidifying system to the probe are above the dewpoint required for the target H2O content. If you are humidifying span gases with NO2, use good engineering judgment to ensure that there is no condensation in the transfer lines, fittings, or valves from the point where humidified gas is mixed with NO2 span gas to the probe. We recommend that you design your setup so that the wall temperatures in the transfer lines, fittings, and valves from the humidifying system to the probe are at least 5 °C above the local sample gas dewpoint. Operate the measurement and sample handling system as you do for emission testing. Make no modifications to the sample handling system to reduce the risk of condensation. Flow humidified gas through the sampling system before this check to allow stabilization of the measurement system's sampling handling system to occur, as it would for an emission test.

(3) Data collection. (i) Start the flow of zero gas.

(ii) Allow for stabilization, accounting for transport delays and the slowest analyzer's full response.

(iii) Start recording data. For this verification you must record data at a frequency greater than or equal to that of the updating-recording frequency used during emission testing. You may not use interpolation or filtering to alter the recorded values.

(iv) Switch the flow to allow the blended span gases to flow to the analyzer. If you intend to use the data from this test to determine t50 for time alignment, record this time as t0.

(v) Allow for transport delays and the slowest analyzer's full response.

(vi) Switch the flow to allow zero gas to flow to the analyzer. If you intend to use the data from this test to determine t50 for time alignment, record this time as t100.

(vii) Allow for transport delays and the slowest analyzer's full response.

(viii) Repeat the steps in paragraphs (d)(3)(iv) through (vii) of this section to record seven full cycles, ending with zero gas flowing to the analyzers.

(ix) Stop recording.

(e) Performance evaluations. (1) If you choose to demonstrate compliance with paragraph (c)(1) of this section, use the data from paragraph (d)(3) of this section to calculate the mean rise time, t10-90, and mean fall time, t90-10, for the continuously combined signal from each analyzer being verified. You may use interpolation between recorded values to determine rise and fall times. If the recording frequency used during emission testing is different from the analyzer's output update frequency, you must use the lower of these two frequencies for this verification. Multiply these times (in seconds) by their respective updating-recording frequencies in Hz (1/second). The resulting product must be at least 5 for both rise time and fall time. If either value is less than 5, increase the updating-recording frequency or adjust the flows or design of the sampling system to increase the rise time and fall time as needed. You may also configure analog or digital filters before recording to increase rise and fall times. In no case may the mean rise time or mean fall time be greater than 10 seconds.

(2) If a measurement system fails the criterion in paragraph (e)(1) of this section, ensure that signals from the system are updated and recorded at a frequency of at least 5 Hz. In no case may the mean rise time or mean fall time be greater than 10 seconds.

(3) If a measurement system fails the criteria in paragraphs (e)(1) and (2) of this section, you may use the measurement system only if the deficiency does not adversely affect your ability to show compliance with the applicable standards in this chapter.

(f) Transformation time, t50, determination. If you choose to determine t50 for purposes of time alignment using data generated in paragraph (d)(3) of this section, calculate the mean t0-50 and the mean t100-50 from the recorded data. Average these two values to determine the final t50 for the purposes of time alignment in accordance with § 1065.650(c)(2)(i).

(g) Optional procedure. Follow the optional procedures in § 1065.308(g), noting that you may use compensating gases mixed with ambient air for oxygen analyzers.

(h) Analyzers with H2O compensation sampling downstream of a sample dryer. You may omit humidifying the span gas as described in this paragraph (h). If an analyzer compensates only for H2O, you may apply the requirements of § 1065.308 instead of the requirements of this section. You may omit humidifying the span gas if you meet the following conditions:

(1) The analyzer is located downstream of a sample dryer.

(2) The maximum value for H2O mole fraction downstream of the dryer must be less than or equal to 0.010. Verify this during each sample dryer verification according to § 1065.342.

(a) Calibrate fuel-flow meters upon initial installation. Follow the instrument manufacturer's instructions and use good engineering judgment to repeat the calibration.

(b) [Reserved]

(c) You may remove system components for off-site calibration. When installing a flow meter with an off-site calibration, we recommend that you consider the effects of the tubing configuration upstream and downstream of the flow meter. We recommend specifying calibration reference quantities that are NIST-traceable within ±0.5% uncertainty.

(a) Calibrate intake-air flow meters upon initial installation. Follow the instrument manufacturer's instructions and use good engineering judgment to repeat the calibration. We recommend using a calibration subsonic venturi, ultrasonic flow meter or laminar flow element. We recommend using calibration reference quantities that are NIST-traceable within ±0.5% uncertainty.

(b) You may remove system components for off-site calibration. When installing a flow meter with an off-site calibration, we recommend that you consider the effects of the tubing configuration upstream and downstream of the flow meter. We recommend specifying calibration reference quantities that are NIST-traceable within ±0.5% uncertainty.

(c) If you use a subsonic venturi or ultrasonic flow meter for intake flow measurement, we recommend that you calibrate it as described in § 1065.340.

(a) Calibrate exhaust-flow meters upon initial installation. Follow the instrument manufacturer's instructions and use good engineering judgment to repeat the calibration. We recommend that you use a calibration subsonic venturi or ultrasonic flow meter and simulate exhaust temperatures by incorporating a heat exchanger between the calibration meter and the exhaust-flow meter. If you can demonstrate that the flow meter to be calibrated is insensitive to exhaust temperatures, you may use other reference meters such as laminar flow elements, which are not commonly designed to withstand typical raw exhaust temperatures. We recommend using calibration reference quantities that are NIST-traceable within ±0.5% uncertainty.

(b) You may remove system components for off-site calibration. When installing a flow meter with an off-site calibration, we recommend that you consider the effects of the tubing configuration upstream and downstream of the flow meter. We recommend specifying calibration reference quantities that are NIST-traceable within ±0.5% uncertainty.

(c) If you use a subsonic venturi or ultrasonic flow meter for raw exhaust flow measurement, we recommend that you calibrate it as described in § 1065.340.

(a) Overview. This section describes how to calibrate flow meters for diluted exhaust constant-volume sampling (CVS) systems.

(b) Scope and frequency. Perform this calibration while the flow meter is installed in its permanent position, except as allowed in paragraph (c) of this section. Perform this calibration after you change any part of the flow configuration upstream or downstream of the flow meter that may affect the flow-meter calibration. Perform this calibration upon initial CVS installation and whenever corrective action does not resolve a failure to meet the diluted exhaust flow verification (i.e., propane check) in § 1065.341.

(c) Ex-situ CFV and SSV calibration. You may remove a CFV or SSV from its permanent position for calibration as long as it meets the following requirements when installed in the CVS:

(1) Upon installation of the CFV or SSV into the CVS, use good engineering judgment to verify that you have not introduced any leaks between the CVS inlet and the venturi.

(2) After ex-situ venturi calibration, you must verify all venturi flow combinations for CFVs or at minimum of 10 flow points for an SSV using the propane check as described in § 1065.341. Your propane check result for each venturi flow point may not exceed the tolerance in § 1065.341(f)(5).

(3) To verify your ex-situ calibration for a CVS with more than a single CFV, perform the following check to verify that there are no flow meter entrance effects that can prevent you from passing this verification.

(i) Use a constant flow device like a CFO kit to deliver a constant flow of propane to the dilution tunnel.

(ii) Measure hydrocarbon concentrations at a minimum of 10 separate flow rates for an SSV flow meter, or at all possible flow combinations for a CFV flow meter, while keeping the flow of propane constant. We recommend selecting CVS flow rates in a random order.

(iii) Measure the concentration of hydrocarbon background in the dilution air at the beginning and end of this test. Subtract the average background concentration from each measurement at each flow point before performing the regression analysis in paragraph (c)(3)(iv) of this section.

(iv) Perform a power regression using all the paired values of flow rate and corrected concentration to obtain a relationship in the form of y = a · x b. Use concentration as the independent variable and flow rate as the dependent variable. For each data point, calculate the difference between the measured flow rate and the value represented by the curve fit. The difference at each point must be less than ±1% of the appropriate regression value. The value of b must be between −1.005 and −0.995. If your results do not meet these limits, take corrective action consistent with § 1065.341(a).

(d) Reference flow meter. Calibrate a CVS flow meter using a reference flow meter such as a subsonic venturi flow meter, a long-radius ASME/NIST flow nozzle, a smooth approach orifice, a laminar flow element, a set of critical flow venturis, or an ultrasonic flow meter. Use a reference flow meter that reports quantities that are NIST-traceable within ±1% uncertainty. Use this reference flow meter's response to flow as the reference value for CVS flow-meter calibration.

(e) Configuration. Calibrate the system with any upstream screens or other restrictions that will be used during testing and that could affect the flow ahead of the CVS flow meter, using good engineering judgment to minimize the effect on the flow distribution. You may not use any upstream screen or other restriction that could affect the flow ahead of the reference flow meter, unless the flow meter has been calibrated with such a restriction. In the case of a free standing SSV reference flow meter, you may not have any upstream screens.

(f) PDP calibration. Calibrate a positive-displacement pump (PDP) to determine a flow-versus-PDP speed equation that accounts for flow leakage across sealing surfaces in the PDP as a function of PDP inlet pressure. Determine unique equation coefficients for each speed at which you operate the PDP. Calibrate a PDP flow meter as follows:

(1) Connect the system as shown in Figure 1 of this section.

(2) Leaks between the calibration flow meter and the PDP must be less than 0.3% of the total flow at the lowest calibrated flow point; for example, at the highest restriction and lowest PDP-speed point.

(3) While the PDP operates, maintain a constant temperature at the PDP inlet within ±2% of the mean absolute inlet temperature, T in.

(4) Set the PDP speed to the first speed point at which you intend to calibrate.

(5) Set the variable restrictor to its wide-open position.

(6) Operate the PDP for at least 3 min to stabilize the system. Continue operating the PDP and record the mean values of at least 30 seconds of sampled data of each of the following quantities:

(i) The mean flow rate of the reference flow meter, n ref. This may include several measurements of different quantities, such as reference meter pressures and temperatures, for calculating n ref.

(ii) The mean temperature at the PDP inlet, T in.

(iii) The mean static absolute pressure at the PDP inlet, p in.

(iv) The mean static absolute pressure at the PDP outlet, p out.

(v) The mean PDP speed, f nPDP.

(7) Incrementally close the restrictor valve to decrease the absolute pressure at the inlet to the PDP, p in.

(8) Repeat the steps in paragraphs (e)(6) and (7) of this section to record data at a minimum of six restrictor positions ranging from the wide open restrictor position to the minimum expected pressure at the PDP inlet or the maximum expected differential (outlet minus inlet) pressure across the PDP during testing.

(9) Calibrate the PDP by using the collected data and the equations in § 1065.640.

(10) Repeat the steps in paragraphs (e)(6) through (9) of this section for each speed at which you operate the PDP.

(11) Use the equations in § 1065.642 to determine the PDP flow equation for emission testing.

(12) Verify the calibration by performing a CVS verification (i.e., propane check) as described in § 1065.341.

(13) During emission testing ensure that the PDP is not operated either below the lowest inlet pressure point or above the highest differential pressure point in the calibration data.

(g) SSV calibration. Calibrate a subsonic venturi (SSV) to determine its calibration coefficient, Cd, for the expected range of inlet pressures. Calibrate an SSV flow meter as follows:

(1) Connect the system as shown in Figure 1 of this section.

(2) Verify that any leaks between the calibration flow meter and the SSV are less than 0.3% of the total flow at the highest restriction.

(3) Start the blower downstream of the SSV.

(4) While the SSV operates, maintain a constant temperature at the SSV inlet within ±2% of the mean absolute inlet temperature, T in.

(5) Set the variable restrictor or variable-speed blower to a flow rate greater than the greatest flow rate expected during testing. You may not extrapolate flow rates beyond calibrated values, so we recommend that you make sure the Reynolds number, Re#, at the SSV throat at the greatest calibrated flow rate is greater than the maximum Re# expected during testing.

(6) Operate the SSV for at least 3 min to stabilize the system. Continue operating the SSV and record the mean of at least 30 seconds of sampled data of each of the following quantities:

(i) The mean flow rate of the reference flow meter n ref. This may include several measurements of different quantities for calculating n ref, such as reference meter pressures and temperatures.

(ii) Optionally, the mean dewpoint of the calibration air,T dew. See § 1065.640 for permissible assumptions.

(iii) The mean temperature at the venturi inlet,T in.

(iv) The mean static absolute pressure at the venturi inlet, P in.

(v) The mean static differential pressure between the static pressure at the venturi inlet and the static pressure at the venturi throat, ΔP SSV.

(7) Incrementally close the restrictor valve or decrease the blower speed to decrease the flow rate.

(8) Repeat the steps in paragraphs (g)(6) and (7) of this section to record data at a minimum of ten flow rates.

(9) Determine an equation to quantify Cd as a function of Re# by using the collected data and the equations in § 1065.640. Section 1065.640 also includes statistical criteria for validating the Cd versus Re# equation.

(10) Verify the calibration by performing a CVS verification (i.e., propane check) as described in § 1065.341 using the new Cd versus Re# equation.

(11) Use the SSV only between the minimum and maximum calibrated Re#. If you want to use the SSV at a lower or higher Re#, you must recalibrate the SSV.

(12) Use the equations in § 1065.642 to determine SSV flow during a test.

(h) CFV calibration. Calibrate a critical-flow venturi (CFV) to verify its discharge coefficient, Cd, up to the highest expected pressure ratio, r, according to § 1065.640. Calibrate a CFV flow meter as follows:

(1) Connect the system as shown in Figure 1 of this section.

(2) Verify that any leaks between the calibration flow meter and the CFV are less than 0.3% of the total flow at the highest restriction.

(3) Start the blower downstream of the CFV.

(4) While the CFV operates, maintain a constant temperature at the CFV inlet within ±2% of the mean absolute inlet temperature, T in.

(5) Set the variable restrictor to its wide-open position. Instead of a variable restrictor, you may alternately vary the pressure downstream of the CFV by varying blower speed or by introducing a controlled leak. Note that some blowers have limitations on nonloaded conditions.

(6) Operate the CFV for at least 3 min to stabilize the system. Continue operating the CFV and record the mean values of at least 30 seconds of sampled data of each of the following quantities:

(i) The mean flow rate of the reference flow meter, n ref. This may include several measurements of different quantities, such as reference meter pressures and temperatures, for calculating n ref.

(ii) The mean dewpoint of the calibration air,T dew. See § 1065.640 for permissible assumptions during emission measurements.

(iii) The mean temperature at the venturi inlet,T in.

(iv) The mean static absolute pressure at the venturi inlet, P in.

(v) The mean static differential pressure between the CFV inlet and the CFV outlet, ΔP CFV.

(7) Incrementally close the restrictor valve or decrease the downstream pressure to decrease the differential pressure across the CFV, ΔpCFV.

(8) Repeat the steps in paragraphs (f)(6) and (7) of this section to record mean data at a minimum of ten restrictor positions, such that you test the fullest practical range of ΔP CFV expected during testing. We do not require that you remove calibration components or CVS components to calibrate at the lowest possible restrictions.

(9) Determine Cd and the highest allowable pressure ratio, r, according to § 1065.640.

(10) Use Cd to determine CFV flow during an emission test. Do not use the CFV above the highest allowed r, as determined in § 1065.640.

(11) Verify the calibration by performing a CVS verification (i.e., propane check) as described in § 1065.341.

(12) If your CVS is configured to operate more than one CFV at a time in parallel, calibrate your CVS by one of the following:

(i) Calibrate every combination of CFVs according to this section and § 1065.640. Refer to § 1065.642 for instructions on calculating flow rates for this option.

(ii) Calibrate each CFV according to this section and § 1065.640. Refer to § 1065.642 for instructions on calculating flow rates for this option.

(i) Ultrasonic flow meter calibration. [Reserved]

This section describes two optional methods, using propane as a tracer gas, to verify CVS and PFD flow streams. You may use good engineering judgment and safe practices to use other tracer gases, such as CO2 or CO. The first method, described in paragraphs (a) through (e) of this section, applies for the CVS diluted exhaust flow measurement system. The first method may also apply for other single-flow measurement systems as described in Table 2 of § 1065.307. Paragraph (g) of this section describes a second method you may use to verify flow measurements in a PFD for determining the PFD dilution ratio.

(a) A propane check uses either a reference mass or a reference flow rate of C3H8 as a tracer gas in a CVS. Note that if you use a reference flow rate, account for any non-ideal gas behavior of C3H8 in the reference flow meter. Refer to §§ 1065.640 and 1065.642, which describe how to calibrate and use certain flow meters. Do not use any ideal gas assumptions in §§ 1065.640 and 1065.642. The propane check compares the calculated mass of injected C3H8 using HC measurements and CVS flow rate measurements with the reference value.

(b) Prepare for the propane check as follows:

(1) If you use a reference mass of C3H8 instead of a reference flow rate, obtain a cylinder charged with C3H8. Determine the reference cylinder's mass of C3H8 within ±0.5% of the amount of C3H8 that you expect to use. You may substitute a C3H8 analytical gas mixture (i.e., a prediluted tracer gas) for pure C3H8. This would be most appropriate for lower flow rates. The analytical gas mixture must meet the specifications in § 1065.750(a)(3).

(2) Select appropriate flow rates for the CVS and C3H8.

(3) Select a C3H8 injection port in the CVS. Select the port location to be as close as practical to the location where you introduce engine exhaust into the CVS, or at some point in the laboratory exhaust tubing upstream of this location. Connect the C3H8 cylinder to the injection system.

(4) Operate and stabilize the CVS.

(5) Preheat or pre-cool any heat exchangers in the sampling system.

(6) Allow heated and cooled components such as sample lines, filters, chillers, and pumps to stabilize at operating temperature.

(7) You may purge the HC sampling system during stabilization.

(8) If applicable, perform a vacuum side leak verification of the HC sampling system as described in § 1065.345.

(9) You may also conduct any other calibrations or verifications on equipment or analyzers.

(c) If you performed the vacuum-side leak verification of the HC sampling system as described in paragraph (b)(8) of this section, you may use the HC contamination procedure in § 1065.520(f) to verify HC contamination. Otherwise, zero, span, and verify contamination of the HC sampling system, as follows:

(1) Select the lowest HC analyzer range that can measure the C3H8 concentration expected for the CVS and C3H8 flow rates.

(2) Zero the HC analyzer using zero air introduced at the analyzer port.

(3) Span the HC analyzer using C3H8 span gas introduced at the analyzer port.

(4) Overflow zero air at the HC probe inlet or into a tee near the outlet of the probe.

(5) Measure the stable HC concentration of the HC sampling system as overflow zero air flows. For batch HC measurement, fill the batch container (such as a bag) and measure the HC overflow concentration.

(6) If the overflow HC concentration exceeds 2 µmol/mol, do not proceed until contamination is eliminated. Determine the source of the contamination and take corrective action, such as cleaning the system or replacing contaminated portions.

(7) When the overflow HC concentration does not exceed 2 µmol/mol, record this value as xTHCinit and use it to correct for HC contamination as described in § 1065.660.

(d) Perform the propane check as follows:

(1) For batch HC sampling, connect clean storage media, such as evacuated bags.

(2) Operate HC measurement instruments according to the instrument manufacturer's instructions.

(3) If you will correct for dilution air background concentrations of HC, measure and record background HC in the dilution air.

(4) Zero any integrating devices.

(5) Begin sampling, and start any flow integrators.

(6) Release the contents of the C3H8 reference cylinder at the rate you selected. If you use a reference flow rate of C3H8, start integrating this flow rate.

(7) Continue to release the cylinder's contents until at least enough C3H8 has been released to ensure accurate quantification of the reference C3H8 and the measured C3H8.

(8) Shut off the C3H8 reference cylinder and continue sampling until you have accounted for time delays due to sample transport and analyzer response.

(9) Stop sampling and stop any integrators.

(e) Perform post-test procedure as follows:

(1) If you used batch sampling, analyze batch samples as soon as practical.

(2) After analyzing HC, correct for contamination and background.

(3) Calculate total C3H8 mass based on your CVS and HC data as described in § 1065.650 (40 CFR 1066.605 for vehicle testing) and § 1065.660, using the molar mass of C3H8, MC3H8, instead of the effective molar mass of HC, MHC.

(4) If you use a reference mass, determine the cylinder's propane mass within ±0.5% and determine the C3H8 reference mass by subtracting the empty cylinder propane mass from the full cylinder propane mass.

(5) Subtract the reference C3H8 mass from the calculated mass. If this difference is within ±2% of the reference mass, the CVS passes this verification. If not, take corrective action as described in paragraph (f) of this section.

(f) A failed propane check might indicate one or more problems requiring corrective action, as follows:

(g) You may verify flow measurements in a PFD (usually dilution air and diluted exhaust streams) for determining the dilution ratio in the PFD using the following method:

(1) Configure the HC sampling system to extract a sample from the PFD's diluted exhaust stream (such as near a PM filter). If the absolute pressure at this location is too low to extract an HC sample, you may sample HC from the PFD's pump exhaust. Use caution when sampling from pump exhaust because an otherwise acceptable pump leak downstream of a PFD diluted exhaust flow meter will cause a false failure of the propane check.

(2) Perform the propane check described in paragraphs (b), (c), and (d) of this section, but sample HC from the PFD's diluted exhaust stream. Inject the propane in the same exhaust stream that the PFD is sampling from (either CVS or raw exhaust stack).

(3) Calculate C3H8 mass, taking into account the dilution from the PFD.

(4) Subtract the reference C3H8 mass from the calculated mass. If this difference is within ±2% of the reference mass, all PFD flow measurements for determining PFD dilution ratio pass this verification. If not, take corrective action as described in paragraph (f) of this section. For PFDs sampling only for PM, the allowed difference is ±5%.

(h) Table 2 of § 1065.307 describes optional verification procedures you may perform instead of linearity verification for certain flow-measurement systems. Performing carbon balance error verification also replaces any required propane checks.

(a) Scope and frequency. If you use a sample dryer as allowed in § 1065.145(e)(2) to remove water from the sample gas, verify the performance upon installation, after major maintenance, for thermal chiller. For osmotic membrane dryers, verify the performance upon installation, after major maintenance, and within 35 days of testing.

(b) Measurement principles. Water can inhibit an analyzer's ability to properly measure the exhaust component of interest and thus is sometimes removed before the sample gas reaches the analyzer. For example water can negatively interfere with a CLD's NOX response through collisional quenching and can positively interfere with an NDIR analyzer by causing a response similar to CO.

(c) System requirements. The sample dryer must meet the specifications as determined in § 1065.145(e)(2) for dewpoint, Tdew, and absolute pressure, ptotal, downstream of the osmotic-membrane dryer or thermal chiller.

(d) Sample dryer verification procedure. Use the following method to determine sample dryer performance. Run this verification with the dryer and associated sampling system operating in the same manner you will use for emission testing (including operation of sample pumps). You may run this verification test on multiple sample dryers sharing the same sampling system at the same time. You may run this verification on the sample dryer alone, but you must use the maximum gas flow rate expected during testing. You may use good engineering judgment to develop a different protocol.

(1) Use PTFE or stainless steel tubing to make necessary connections.

(2) Humidify room air, purified N2, or purified air by bubbling it through distilled H2O in a sealed vessel or use a device that injects distilled H2O as vapor into a controlled gas flow to humidify the gas to the highest sample H2O content that you estimate during emission sampling.

(3) Introduce the humidified gas upstream of the sample dryer. You may disconnect the transfer line from the probe and introduce the humidified gas at the inlet of the transfer line of the sample system used during testing. You may use the sample pumps in the sample system to draw gas through the vessel.

(4) Maintain the sample lines, fittings, and valves from the location where the humidified gas water content is measured to the inlet of the sampling system at a temperature at least 5 °C above the local humidified gas dewpoint. For dryers used in NOX sample systems, verify the sample system components used in this verification prevent aqueous condensation as required in § 1065.145(d)(1)(i). We recommend that the sample system components be maintained at least 5 °C above the local humidified gas dewpoint to prevent aqueous condensation.

(5) Measure the humidified gas dewpoint, Tdew, and absolute pressure, ptotal, as close as possible to the inlet of the sample dryer or inlet of the sample system to verify the water content is at least as high as the highest value that you estimated during emission sampling. You may verify the water content based on any humidity parameter (e.g. mole fraction water, local dewpoint, or absolute humidity).

(6) Measure the humidified gas dewpoint, Tdew, and absolute pressure, ptotal, as close as possible to the outlet of the sample dryer. Note that the dewpoint changes with absolute pressure. If the dewpoint at the sample dryer outlet is measured at a different pressure, then this reading must be corrected to the dewpoint at the sample dryer absolute pressure, ptotal.

(7) The sample dryer meets the verification if the dewpoint at the sample dryer pressure as measured in paragraph (d)(6) of this section is less than the dewpoint corresponding to the sample dryer specifications as determined in § 1065.145(e)(2) plus 2 °C or if the mole fraction of water as measured in (d)(6) is less than the corresponding sample dryer specifications plus 0.002 mol/mol.

(e) Alternate sample dryer verification procedure. The following method may be used in place of the sample dryer verification procedure in (d) of this section. If you use a humidity sensor for continuous monitoring of dewpoint at the sample dryer outlet you may skip the performance check in § 1065.342(d), but you must make sure that the dryer outlet humidity is at or below the minimum value used for quench, interference, and compensation checks.

(a) Scope and frequency. Verify that there are no significant vacuum-side leaks using one of the leak tests described in this section. For laboratory testing, perform the vacuum-side leak verification upon initial sampling system installation, within 8 hours before the start of the first test interval of each duty-cycle sequence, and after maintenance such as pre-filter changes. For field testing, perform the vacuum-side leak verification after each installation of the sampling system on the vehicle, prior to the start of the field test, and after maintenance such as pre-filter changes. This verification does not apply to any full-flow portion of a CVS dilution system.

(b) Measurement principles. A leak may be detected either by measuring a small amount of flow when there should be zero flow, or by detecting the dilution of a known concentration of span gas when it flows through the vacuum side of a sampling system.

(c) Low-flow leak test. Test a sampling system for low-flow leaks as follows:

(1) Seal the probe end of the system by taking one of the following steps:

(i) Cap or plug the end of the sample probe.

(ii) Disconnect the transfer line at the probe and cap or plug the transfer line.

(iii) Close a leak-tight valve located in the sample transfer line within 92 cm of the probe.

(2) Operate all vacuum pumps. After stabilizing, verify that the flow through the vacuum-side of the sampling system is less than 0.5% of the system's normal in-use flow rate. You may estimate typical analyzer and bypass flows as an approximation of the system's normal in-use flow rate.

(d) Dilution-of-span-gas leak test. You may use any gas analyzer for this test. If you use a FID for this test, correct for any HC contamination in the sampling system according to § 1065.660. If you use an O2 analyzer described in § 1065.280 for this test, you may use purified N2 to detect a leak. To avoid misleading results from this test, we recommend using only analyzers that have a repeatability of 0.5% or better at the reference gas concentration used for this test. Perform a vacuum-side leak test as follows:

(1) Prepare a gas analyzer as you would for emission testing.

(2) Supply reference gas to the analyzer span port and record the measured value.

(3) Route overflow reference gas to the inlet of the sample probe or at a tee fitting in the transfer line near the exit of the probe. You may use a valve upstream of the overflow fitting to prevent overflow of reference gas out of the inlet of the probe, but you must then provide an overflow vent in the overflow supply line.

(4) Verify that the measured overflow reference gas concentration is within ±0.5% of the concentration measured in paragraph (d)(2) of this section. A measured value lower than expected indicates a leak, but a value higher than expected may indicate a problem with the reference gas or the analyzer itself. A measured value higher than expected does not indicate a leak.

(e) Vacuum-decay leak test. To perform this test you must apply a vacuum to the vacuum-side volume of your sampling system and then observe the leak rate of your system as a decay in the applied vacuum. To perform this test you must know the vacuum-side volume of your sampling system to within ±10% of its true volume. For this test you must also use measurement instruments that meet the specifications of subpart C of this part and of this subpart D. Perform a vacuum-decay leak test as follows:

(1) Seal the probe end of the system as close to the probe opening as possible by taking one of the following steps:

(i) Cap or plug the end of the sample probe.

(ii) Disconnect the transfer line at the probe and cap or plug the transfer line.

(iii) Close a leak-tight valve located in the sample transfer line within 92 cm of the probe.

(2) Operate all vacuum pumps. Draw a vacuum that is representative of normal operating conditions. In the case of sample bags, we recommend that you repeat your normal sample bag pump-down procedure twice to minimize any trapped volumes.

(3) Turn off the sample pumps and seal the system. Measure and record the absolute pressure of the trapped gas and optionally the system absolute temperature. Wait long enough for any transients to settle and long enough for a leak at 0.5% to have caused a pressure change of at least 10 times the resolution of the pressure transducer, then again record the pressure and optionally temperature.

(4) Calculate the leak flow rate based on an assumed value of zero for pumped-down bag volumes and based on known values for the sample system volume, the initial and final pressures, optional temperatures, and elapsed time. Using the calculations specified in § 1065.644, verify that the vacuum-decay leak flow rate is less than 0.5% of the system's normal in-use flow rate.

(a) Scope and frequency. If you measure CO2 using an NDIR analyzer, verify the amount of H2O interference after initial analyzer installation and after major maintenance.

(b) Measurement principles. H2O can interfere with an NDIR analyzer's response to CO2.

If the NDIR analyzer uses compensation algorithms that utilize measurements of other gases to meet this interference verification, simultaneously conduct these other measurements to test the compensation algorithms during the analyzer interference verification.

(c) System requirements. A CO2 NDIR analyzer must have an H2O interference that is within (0.0 ±0.4) mmol/mol, though we strongly recommend a lower interference that is within (0.0 ±0.2) mmol/mol.

(d) Procedure. Perform the interference verification as follows:

(1) Start, operate, zero, and span the CO2 NDIR analyzer as you would before an emission test. If the sample is passed through a dryer during emission testing, you may run this verification test with the dryer if it meets the requirements of § 1065.342. Operate the dryer at the same conditions as you will for an emission test. You may also run this verification test without the sample dryer.

(2) Create a humidified test gas by bubbling zero gas that meets the specifications in § 1065.750 through distilled H2O in a sealed vessel or use a device that introduces distilled H2O as vapor into a controlled gas flow. If the sample does not pass through a dryer during emission testing, humidify your test gas to an H2O level at or above the maximum expected during emission testing. If the sample passes through a dryer during emission testing, you must humidify your test gas to an H2O level at or above the level determined in § 1065.145(e)(2) for that dryer.

(3) Introduce the humidified test gas into the sample system. You may introduce it downstream of any sample dryer, if one is used during testing.

(4) If the sample is not passed through a dryer during this verification test, measure the H2O mole fraction, xH2O, of the humidified test gas, as close as possible to the inlet of the analyzer. For example, measure dewpoint, Tdew, and absolute pressure, ptotal, to calculate xH2O. Verify that the H2O content meets the requirement in paragraph (d)(2) of this section. If the sample is passed through a dryer during this verification test, you must verify that the H2O content of the humidified test gas downstream of the vessel meets the requirement in paragraph (d)(2) of this section based on either direct measurement of the H2O content (e.g., dewpoint and pressure) or an estimate based on the vessel pressure and temperature. Use good engineering judgment to estimate the H2O content. For example, you may use previous direct measurements of H2O content to verify the vessel's level of saturation.

(5) If a sample dryer is not used in this verification test, use good engineering judgment to prevent condensation in the transfer lines, fittings, or valves from the point where xH2O is measured to the analyzer. We recommend that you design your system so the wall temperatures in the transfer lines, fittings, and valves from the point where xH2O is measured to the analyzer are at least 5 °C above the local sample gas dewpoint.

(6) Allow time for the analyzer response to stabilize. Stabilization time may include time to purge the transfer line and to account for analyzer response.

(7) While the analyzer measures the sample's concentration, record 30 seconds of sampled data. Calculate the arithmetic mean of this data. The analyzer meets the interference verification if this value is within (0.0 ±0.4) mmol/mol.

(e) Exceptions. The following exceptions apply:

(1) You may omit this verification if you can show by engineering analysis that for your CO2 sampling system and your emission-calculation procedures, the H2O interference for your CO2 NDIR analyzer always affects your brake-specific emission results within ±0.5% of each of the applicable standards in this chapter. This specification also applies for vehicle testing, except that it relates to emission results in g/mile or g/kilometer.

(2) You may use a CO2 NDIR analyzer that you determine does not meet this verification, as long as you try to correct the problem and the measurement deficiency does not adversely affect your ability to show that engines comply with all applicable emission standards.

(a) Scope and frequency. If you measure CO using an NDIR analyzer, verify the amount of H2O and CO2 interference after initial analyzer installation and after major maintenance.

(b) Measurement principles. H2O and CO2 can positively interfere with an NDIR analyzer by causing a response similar to CO. If the NDIR analyzer uses compensation algorithms that utilize measurements of other gases to meet this interference verification, simultaneously conduct these other measurements to test the compensation algorithms during the analyzer interference verification.

(c) System requirements. A CO NDIR analyzer must have combined H2O and CO2 interference that is within ±2 % of the flow-weighted mean concentration of CO expected at the standard, though we strongly recommend a lower interference that is within ±1%.

(d) Procedure. Perform the interference verification as follows:

(1) Start, operate, zero, and span the CO NDIR analyzer as you would before an emission test. If the sample is passed through a dryer during emission testing, you may run this verification test with the dryer if it meets the requirements of § 1065.342. Operate the dryer at the same conditions as you will for an emission test. You may also run this verification test without the sample dryer.

(2) Create a humidified CO2 test gas by bubbling a CO2 span gas that meets the specifications in § 1065.750 through distilled H2O in a sealed vessel or use a device that introduces distilled H2O as vapor into a controlled gas flow. If the sample does not pass through a dryer during emission testing, humidify your test gas to an H2O level at or above the maximum expected during emission testing. If the sample passes through a dryer during emission testing, you must humidify your test gas to an H2O at or above the level determined in § 1065.145(e)(2) for that dryer. Use a CO2 span gas concentration at least as high as the maximum expected during testing.

(3) Introduce the humidified CO2 test gas into the sample system. You may introduce it downstream of any sample dryer, if one is used during testing.

(4) If the sample is not passed through a dryer during this verification test, measure the H2O mole fraction, xH2O, of the humidified CO2 test gas as close as possible to the inlet of the analyzer. For example, measure dewpoint, Tdew, and absolute pressure, ptotal, to calculate xH2O. Verify that the H2O content meets the requirement in paragraph (d)(2) of this section. If the sample is passed through a dryer during this verification test, you must verify that the H2O content of the humidified test gas downstream of the vessel meets the requirement in paragraph (d)(2) of this section based on either direct measurement of the H2O content (e.g., dewpoint and pressure) or an estimate based on the vessel pressure and temperature. Use good engineering judgment to estimate the H2O content. For example, you may use previous direct measurements of H2O content to verify the vessel's level of saturation.

(5) If a sample dryer is not used in this verification test, use good engineering judgment to prevent condensation in the transfer lines, fittings, or valves from the point where xH2O is measured to the analyzer. We recommend that you design your system so that the wall temperatures in the transfer lines, fittings, and valves from the point where xH2O is measured to the analyzer are at least 5 °C above the local sample gas dewpoint.

(6) Allow time for the analyzer response to stabilize. Stabilization time may include time to purge the transfer line and to account for analyzer response.

(7) While the analyzer measures the sample's concentration, record its output for 30 seconds. Calculate the arithmetic mean of this data.

(8) The analyzer meets the interference verification if the result of paragraph (d)(7) of this section meets the tolerance in paragraph (c) of this section.

(9) You may also run interference procedures for CO2 and H2O separately. If the CO2 and H2O levels used are higher than the maximum levels expected during testing, you may scale down each observed interference value by multiplying the observed interference by the ratio of the maximum expected concentration value to the actual value used during this procedure. You may run separate interference concentrations of H2O (down to 0.025 mol/mol H2O content) that are lower than the maximum levels expected during testing, but you must scale up the observed H2O interference by multiplying the observed interference by the ratio of the maximum expected H2O concentration value to the actual value used during this procedure. The sum of the two scaled interference values must meet the tolerance in paragraph (c) of this section.

(e) Exceptions. The following exceptions apply:

(1) You may omit this verification if you can show by engineering analysis that for your CO sampling system and your emission-calculation procedures, the combined CO2 and H2O interference for your CO NDIR analyzer always affects your brake-specific CO emission results within ±0.5% of the applicable CO standard.

(2) You may use a CO NDIR analyzer that you determine does not meet this verification, as long as you try to correct the problem and the measurement deficiency does not adversely affect your ability to show that engines comply with all applicable emission standards.

(a) Scope and frequency. For all FID analyzers, calibrate the FID upon initial installation. Repeat the calibration as needed using good engineering judgment. For a FID that measures THC, perform the following steps:

(1) Optimize the response to various hydrocarbons after initial analyzer installation and after major maintenance as described in paragraph (c) of this section.

(2) Determine the methane (CH4) response factor after initial analyzer installation and after major maintenance as described in paragraph (d) of this section.

(3) If you determine NMNEHC by subtracting from measured THC, determine the ethane (C2H6) response factor after initial analyzer installation and after major maintenance as described in paragraph (f) of this section. Verify the C2H6 response within 185 days before testing as described in paragraph (f) of this section.

(4) For any gaseous-fueled engine, including dual-fuel and flexible-fuel engines, you may determine the methane (CH4) and ethane (C2H6) response factors as a function of the molar water concentration in the raw or diluted exhaust. If you choose the option in this paragraph (a)(4), generate and verify the humidity level (or fraction) as described in § 1065.365(d)(11).

(b) Calibration. Use good engineering judgment to develop a calibration procedure, such as one based on the FID-analyzer manufacturer's instructions and recommended frequency for calibrating the FID. Alternately, you may remove system components for off-site calibration. For a FID that measures THC, calibrate using C3H8 calibration gases that meet the specifications of § 1065.750. For a FID that measures CH4, calibrate using CH4 calibration gases that meet the specifications of § 1065.750. We recommend FID analyzer zero and span gases that contain approximately the flow-weighted mean concentration of O2 expected during testing. If you use a FID to measure CH4 downstream of a nonmethane cutter, you may calibrate that FID using CH4 calibration gases with the cutter. Regardless of the calibration gas composition, calibrate on a carbon number basis of one (C1). For example, if you use a C3H8 span gas of concentration 200 µmol/mol, span the FID to respond with a value of 600 µmol/mol. As another example, if you use a CH4 span gas with a concentration of 200 µmol/mol, span the FID to respond with a value of 200 µmol/mol.

(c) THC FID response optimization. This procedure is only for FID analyzers that measure THC. Use good engineering judgment for initial instrument start-up and basic operating adjustment using FID fuel and zero air. Heated FIDs must be within their required operating temperature ranges. Optimize FID response at the most common analyzer range expected during emission testing. Optimization involves adjusting flows and pressures of FID fuel, burner air, and sample to minimize response variations to various hydrocarbon species in the exhaust. Use good engineering judgment to trade off peak FID response to propane calibration gases to achieve minimal response variations to different hydrocarbon species. For an example of trading off response to propane for relative responses to other hydrocarbon species, see SAE 770141 (incorporated by reference in § 1065.1010). Determine the optimum flow rates and/or pressures for FID fuel, burner air, and sample and record them for future reference.

(d) THC FID CH4 response factor determination. This procedure is only for FID analyzers that measure THC. Since FID analyzers generally have a different response to CH4 versus C3H8, determine the THC-FID analyzer's CH4 response factor, RFCH4[THC-FID], after FID optimization. Use the most recent RFCH4[THC-FID] measured according to this section in the calculations for HC determination described in § 1065.660 to compensate for CH4 response. Determine RFCH4[THC-FID] as follows, noting that you do not determine RFCH4[THC-FID] for FIDs that are calibrated and spanned using CH4 with a nonmethane cutter:

(1) Select a C3 H8 span gas concentration that you use to span your analyzers before emission testing. Use only span gases that meet the specifications of § 1065.750. Record the C3H8 concentration of the gas.

(2) Select a CH4 span gas concentration that you use to span your analyzers before emission testing. Use only span gases that meet the specifications of § 1065.750. Record the CH4 concentration of the gas.

(3) Start and operate the FID analyzer according to the manufacturer's instructions.

(4) Confirm that the FID analyzer has been calibrated using C3H8. Calibrate on a carbon number basis of one (C1). For example, if you use a C3 H8 span gas of concentration 200 µmol/mol, span the FID to respond with a value of 600 µmol/mol.

(5) Zero the FID with a zero gas that you use for emission testing.

(6) Span the FID with the C3H8 span gas that you selected under paragraph (d)(1) of this section.

(7) Introduce the CH4 span gas that you selected under paragraph (d)(2) of this section into the FID analyzer.

(8) Allow time for the analyzer response to stabilize. Stabilization time may include time to purge the analyzer and to account for its response.

(9) While the analyzer measures the CH4 concentration, record 30 seconds of sampled data. Calculate the arithmetic mean of these values.

(10) For analyzers with multiple ranges, you need to perform the procedure in this paragraph (d) only on a single range.

(11) Divide the mean measured concentration by the recorded span concentration of the CH4 calibration gas. The result is the FID analyzer's response factor for CH4, RF CH4[THC-FID].

(12) Determine the response factor as a function of molar water concentration and use this response factor to account for the CH4 response for NMHC determination described in § 1065.660(b)(2)(iii). Humidify the CH4 span gas as described in § 1065.365(d)(11) and repeat the steps in paragraphs (d)(7) through (9) of this section until measurements are complete for each setpoint in the selected range. Divide each mean measured CH4 concentration by the recorded span concentration of the CH4 calibration gas, adjusted for water content, to determine the FID analyzer's CH4 response factor, RFCH4[THC-FID]. Use the CH4 response factors at the different setpoints to create a functional relationship between response factor and molar water concentration, downstream of the last sample dryer if any sample dryers are present. Use this functional relationship to determine the response factor during an emission test.

(e) THC FID CH4 response verification. This procedure is only for FID analyzers that measure THC. Verify RFCH4[THC-FID] as follows:

(1) Perform a CH4 response factor determination as described in paragraph (d) of this section. If the resulting value of RFCH4[THC-FID] is within ±5% of its most recent previously determined value, the THC FID passes the CH4 response verification. For example, if the most recent previous value for RF CH4[THC-FID] was 1.05 and it increased by 0.05 to become 1.10 or it decreased by 0.05 to become 1.00, either case would be acceptable because ±4.8% is less than ±5%.

(2) If RF CH4[THC-FID] is not within the tolerance specified in paragraph (e)(1) of this section, use good engineering judgment to verify that the flow rates and/or pressures of FID fuel, burner air, and sample are at their most recent previously recorded values, as determined in paragraph (c) of this section. You may adjust these flow rates as necessary. Then determine the RF CH4[THC-FID] as described in paragraph (d) of this section and verify that it is within the tolerance specified in this paragraph (e).

(3) If RF CH4[THC-FID] is not within the tolerance specified in this paragraph (e), re-optimize the FID response as described in paragraph (c) of this section.

(4) Determine a new RFCH4[THC-FID] as described in paragraph (d) of this section. Use this new value of RF CH4[THC-FID] in the calculations for HC determination, as described in § 1065.660.

(5) For analyzers with multiple ranges, you need to perform the procedure in this paragraph (e) only on a single range.

(f) THC FID C2H6 response factor determination. This procedure is only for FID analyzers that measure THC. Since FID analyzers generally have a different response to C2H6 than C3H8, determine the THC-FID analyzer's C2H6 response factor, RFC2H6[THC-FID], after FID optimization using the procedure described in paragraph (d) of this section, replacing CH4 with C2H6. Use the most recent RFC2H6[THC-FID] measured according to this section in the calculations for HC determination described in § 1065.660 to compensate for C2H6 response.

(a) Scope and frequency. If you use FID analyzers for raw exhaust measurements from engines that operate in a non-stoichiometric mode of combustion (e.g., compression-ignition, lean-burn), verify the amount of FID O2 interference upon initial installation and after major maintenance.

(b) Measurement principles. Changes in O2 concentration in raw exhaust can affect FID response by changing FID flame temperature. Optimize FID fuel, burner air, and sample flow to meet this verification. Verify FID performance with the compensation algorithms for FID O2 interference that you have active during an emission test.

(c) System requirements. Any FID analyzer used during testing must meet the FID O2 interference verification according to the procedure in this section.

(d) Procedure. Determine FID O2 interference as follows, noting that you may use one or more gas dividers to create the reference gas concentrations that are required to perform this verification:

(1) Select three span reference gases that contain a C3H8 concentration that you use to span your analyzers before emission testing. Use only span gases that meet the specifications of § 1065.750. You may use CH4 span reference gases for FIDs calibrated on CH4 with a nonmethane cutter. Select the three balance gas concentrations such that the concentrations of O2 and N2 represent the minimum, maximum, and average O2 concentrations expected during testing. The requirement for using the average O2 concentration can be removed if you choose to calibrate the FID with span gas balanced with the average expected oxygen concentration.

(2) Confirm that the FID analyzer meets all the specifications of § 1065.360.

(3) Start and operate the FID analyzer as you would before an emission test. Regardless of the FID burner's air source during testing, use zero air as the FID burner's air source for this verification.

(4) Zero the FID analyzer using the zero gas used during emission testing.

(5) Span the FID analyzer using a span gas that you use during emission testing.

(6) Check the zero response of the FID analyzer using the zero gas used during emission testing. If the mean zero response of 30 seconds of sampled data is within ±0.5% of the span reference value used in paragraph (d)(5) of this section, then proceed to the next step; otherwise restart the procedure at paragraph (d)(4) of this section.

(7) Check the analyzer response using the span gas that has the minimum concentration of O2 expected during testing. Record the mean response of 30 seconds of stabilized sample data as xO2minHC.

(8) Check the zero response of the FID analyzer using the zero gas used during emission testing. If the mean zero response of 30 seconds of stabilized sample data is within ±0.5% of the span reference value used in paragraph (d)(5) of this section, then proceed to the next step; otherwise restart the procedure at paragraph (d)(4) of this section.

(9) Check the analyzer response using the span gas that has the average concentration of O2 expected during testing. Record the mean response of 30 seconds of stabilized sample data as xO2avgHC.

(10) Check the zero response of the FID analyzer using the zero gas used during emission testing. If the mean zero response of 30 seconds of stabilized sample data is within ±0.5% of the span reference value used in paragraph (d)(5) of this section, proceed to the next step; otherwise restart the procedure at paragraph (d)(4) of this section.

(11) Check the analyzer response using the span gas that has the maximum concentration of O2 expected during testing. Record the mean response of 30 seconds of stabilized sample data as xO2maxHC.

(12) Check the zero response of the FID analyzer using the zero gas used during emission testing. If the mean zero response of 30 seconds of stabilized sample data is within ±0.5% of the span reference value used in paragraph (d)(5) of this section, then proceed to the next step; otherwise restart the procedure at paragraph (d)(4) of this section.

(13) Calculate the percent difference between xO2maxHC and its reference gas concentration. Calculate the percent difference between xO2avgHC and its reference gas concentration. Calculate the percent difference between xO2minHC and its reference gas concentration. Determine the maximum percent difference of the three. This is the O2 interference.

(14) If the O2 interference is within ±2%, the FID passes the O2 interference verification; otherwise perform one or more of the following to address the deficiency:

(i) Repeat the verification to determine if a mistake was made during the procedure.

(ii) Select zero and span gases for emission testing that contain higher or lower O2 concentrations and repeat the verification.

(iii) Adjust FID burner air, fuel, and sample flow rates. Note that if you adjust these flow rates on a THC FID to meet the O2 interference verification, you have reset RFCH4 for the next RFCH4 verification according to § 1065.360. Repeat the O2 interference verification after adjustment and determine RFCH4.

(iv) Repair or replace the FID and repeat the O2 interference verification.

(v) Demonstrate that the deficiency does not adversely affect your ability to demonstrate compliance with the applicable emission standards.

(15) For analyzers with multiple ranges, you need to perform the procedure in this paragraph (d) only on a single range.

(a) Scope and frequency. If you use a FID analyzer and a nonmethane cutter (NMC) to measure methane (CH4), determine the nonmethane cutter's penetration fractions of methane, PFCH4, and ethane, PFC2H6. As detailed in this section, these penetration fractions may be determined as a combination of NMC penetration fractions and FID analyzer response factors, depending on your particular NMC and FID analyzer configuration. Perform this verification after installing the nonmethane cutter. Repeat this verification within 185 days of testing to verify that the catalytic activity of the cutter has not deteriorated. Note that because nonmethane cutters can deteriorate rapidly and without warning if they are operated outside of certain ranges of gas concentrations and outside of certain temperature ranges, good engineering judgment may dictate that you determine a nonmethane cutter's penetration fractions more frequently.

(b) Measurement principles. A nonmethane cutter is a heated catalyst that removes nonmethane hydrocarbons from an exhaust sample stream before the FID analyzer measures the remaining hydrocarbon concentration. An ideal nonmethane cutter would have a CH4 penetration fraction, PFCH4, of 1.000, and the penetration fraction for all other nonmethane hydrocarbons would be 0.000, as represented by PFC2H6. The emission calculations in § 1065.660 use the measured values from this verification to account for less than ideal NMC performance.

(c) System requirements. We do not limit NMC penetration fractions to a certain range. However, we recommend that you optimize a nonmethane cutter by adjusting its temperature to achieve a PFCH4 >0.85 and a PFC2H6 <0.02, as determined by paragraphs (d), (e), or (f) of this section, as applicable. If we use a nonmethane cutter for testing, it will meet this recommendation. If adjusting NMC temperature does not result in achieving both of these specifications simultaneously, we recommend that you replace the catalyst material. Use the most recently determined penetration values from this section to calculate HC emissions according to § 1065.660 and § 1065.665 as applicable.

(d) Procedure for a FID calibrated with the NMC. The method described in this paragraph (d) is recommended over the procedures specified in paragraphs (e) and (f) of this section and required for any gaseous-fueled engine, including dual-fuel and flexible-fuel engines. If your FID arrangement is such that a FID is always calibrated to measure CH4 with the NMC, then span that FID with the NMC using a CH4 span gas, set the product of that FID's CH4 response factor and CH4 penetration fraction, RFPFCH4[NMC-FID], equal to 1.0 for all emission calculations, and determine its combined C2H6 response factor and C2H6 penetration fraction, RFPFC2H6[NMC-FID], as follows. For any gaseous-fueled engine, including dual-fuel and flexible-fuel engines, you must determine the CH4 penetration fraction, PFCH4[NMC-FID], and C2H6 response factor and C2H6 penetration fraction, RFPFC2H6[NMC-FID], as a function of the molar water concentration in the raw or diluted exhaust as described in paragraphs (d)(10) and (12) of this section. Generate and verify the humidity generation as described in paragraph (d)(11) of this section. When using the option in this paragraph (d), note that the FID's CH4 penetration fraction, PFCH4[NMC-FID], is set equal to 1.0 only for 0% molar water concentration. You are not required to meet the recommended lower limit for PFCH4 of greater than 0.85 for any of the penetration fractions generated as a function of molar water concentration.

(1) Select CH4 and C2H6 analytical gas mixtures and ensure that both mixtures meet the specifications of § 1065.750. Select a CH4 concentration that you would use for spanning the FID during emission testing and select a C2H6 concentration that is typical of the peak NMHC concentration expected at the hydrocarbon standard or equal to the THC analyzer's span value. For CH4 analyzers with multiple ranges, perform this procedure on the highest range used for emission testing.

(2) Start, operate, and optimize the nonmethane cutter according to the manufacturer's instructions, including any temperature optimization.

(3) Confirm that the FID analyzer meets all the specifications of § 1065.360.

(4) Start and operate the FID analyzer according to the manufacturer's instructions.

(5) Zero and span the FID with the nonmethane cutter as you would during emission testing. Span the FID through the cutter by using CH4 span gas.

(6) Introduce the C2H6 analytical gas mixture upstream of the nonmethane cutter. Use good engineering judgment to address the effect of hydrocarbon contamination if your point of introduction is vastly different from the point of zero/span gas introduction.

(7) Allow time for the analyzer response to stabilize. Stabilization time may include time to purge the nonmethane cutter and to account for the analyzer's response.

(8) While the analyzer measures a stable concentration, record 30 seconds of sampled data. Calculate the arithmetic mean of these data points.

(9) Divide the mean C2H6 concentration by the reference concentration of C2H6, converted to a C1 basis. The result is the C2H6 combined response factor and penetration fraction, RFPFC2H6[NMC-FID]. Use this combined C2H6 response factor and C2H6 penetration fraction and the product of the CH4 response factor and CH4 penetration fraction, RFPFCH4[NMC-FID], set to 1.0 in emission calculations according to § 1065.660(b)(2)(i) or (d)(1)(i) or § 1065.665, as applicable.

(10) Determine the combined C2H6 response factor and C2H6 penetration fraction as a function of molar water concentration and use it to account for C2H6 response factor and C2H6 penetration fraction for NMHC determination as described in § 1065.660(b)(2)(iii) and for CH4 determination in § 1065.660(d)(1)(iii). Humidify the C2H6 analytical gas mixture as described in paragraph (d)(11) of this section. Repeat the steps in paragraphs (d)(6) through (8) of this section until measurements are complete for each setpoint in the selected range. Divide each mean measured C2H6 concentration by the reference concentration of C2H6, converted to a C1-basis and adjusted for water content to determine the FID analyzer's combined C2H6 response factor and C2H6 penetration fraction, RFPFC2H6[NMC-FID]. Use RFPFC2H6[NMC-FID] at the different setpoints to create a functional relationship between the combined response factor and penetration fraction and molar water concentration, downstream of the last sample dryer if any sample dryers are present. Use this functional relationship to determine the combined response factor and penetration fraction during the emission test.

(11) Create a humidified test gas by bubbling the analytical gas mixture that meets the specifications in § 1065.750 through distilled H2O in a sealed vessel or use a device that introduces distilled H2O as vapor into a controlled gas flow. If the sample does not pass through a dryer during emission testing, generate at least five different H2O concentrations that cover the range from less than the minimum expected to greater than the maximum expected water concentration during testing. Use good engineering judgment to determine the target concentrations. For analyzers where the sample passes through a dryer during emission testing, humidify your test gas to an H2O level at or above the level determined in § 1065.145(e)(2) for that dryer and determine a single wet analyzer response to the dehumidified sample. Heat all transfer lines from the water generation system to a temperature at least 5 °C higher than the highest dewpoint generated. Determine H2O concentration as an average value over intervals of at least 30 seconds. Monitor the humidified sample stream with a dewpoint analyzer, relative humidity sensor, FTIR, NDIR, or other water analyzer during each test or, if the humidity generator achieves humidity levels with controlled flow rates, validate the instrument within 370 days before testing and after major maintenance using one of the following methods:

(i) Determine the linearity of each flow metering device. Use one or more reference flow meters to measure the humidity generator's flow rates and verify the H2O level value based on the humidity generator manufacturer's recommendations and good engineering judgment. We recommend that you utilize at least 10 flow rates for each flow-metering device.

(ii) Perform validation testing based on monitoring the humidified stream with a dewpoint analyzer, relative humidity sensor, FTIR, NDIR, or other water analyzer as described in this paragraph (d)(11). Compare the measured humidity to the humidity generator's value. Verify overall linearity performance for the generated humidity as described in § 1065.307 using the criteria for other dewpoint measurements or confirm all measured values are within ±2% of the target mole fraction. In the case of dry gas, the measured value may not exceed 0.002 mole fraction.

(iii) Follow the performance requirements in § 1065.307(b) if the humidity generator does not meet validation criteria.

(12) Determine the CH4 penetration fraction as a function of molar water concentration and use this penetration fraction for NMHC determination in § 1065.660(b)(2)(iii) and for CH4 determination in § 1065.660(d)(1)(iii). Repeat the steps in paragraphs (d)(6) through (11) of this section, but with the CH4 analytical gas mixture instead of C2H6. Use this functional relationship to determine the penetration fraction during the emission test.

(e) Procedure for a FID calibrated with propane, bypassing the NMC. If you use a single FID for THC and CH4 determination with an NMC that is calibrated with propane, C3H8, by bypassing the NMC, determine its penetration fractions, PFC2H6[NMC-FID] and PFCH4[NMC-FID], as follows:

(1) Select CH4 and C2H6 analytical gas mixtures and ensure that both mixtures meet the specifications of § 1065.750. Select a CH4 concentration that you would use for spanning the FID during emission testing and select a C2H6 concentration that is typical of the peak NMHC concentration expected at the hydrocarbon standard and the C2H6 concentration typical of the peak total hydrocarbon (THC) concentration expected at the hydrocarbon standard or equal to the THC analyzer's span value. For CH4 analyzers with multiple ranges, perform this procedure on the highest range used for emission testing.

(2) Start and operate the nonmethane cutter according to the manufacturer's instructions, including any temperature optimization.

(3) Confirm that the FID analyzer meets all the specifications of § 1065.360.

(4) Start and operate the FID analyzer according to the manufacturer's instructions.

(5) Zero and span the FID as you would during emission testing. Span the FID by bypassing the cutter and by using C3H8 span gas.

(6) Introduce the C2H6 analytical gas mixture upstream of the nonmethane cutter. Use good engineering judgment to address the effect of hydrocarbon contamination if your point of introduction is vastly different from the point of zero/span gas introduction.

(7) Allow time for the analyzer response to stabilize. Stabilization time may include time to purge the nonmethane cutter and to account for the analyzer's response.

(8) While the analyzer measures a stable concentration, record 30 seconds of sampled data. Calculate the arithmetic mean of these data points.

(9) Reroute the flow path to bypass the nonmethane cutter, introduce the C2H6 analytical gas mixture, and repeat the steps in paragraph (e)(7) through (e)(8) of this section.

(10) Divide the mean C2H6 concentration measured through the nonmethane cutter by the mean C2H6 concentration measured after bypassing the nonmethane cutter. The result is the C2H6 penetration fraction, PFC2H6[NMC-FID]. Use this penetration fraction according to § 1065.660(b)(2)(ii), § 1065.660(d)(1)(ii), or § 1065.665, as applicable.

(11) Repeat the steps in paragraphs (e)(6) through (e)(10) of this section, but with the CH4 analytical gas mixture instead of C2H6. The result will be the CH4 penetration fraction, PFCH4[NMC-FID]. Use this penetration fraction according to § 1065.660(b)(2)(ii), § 1065.660(c)(1)(ii), or § 1065.665, as applicable.

(f) Procedure for a FID calibrated with CH4, bypassing the NMC. If you use a FID with an NMC that is calibrated with CH4, by bypassing the NMC, determine its combined ethane (C2H6) response factor and penetration fraction, RFPFC2H6[NMC-FID], as well as its CH4 penetration fraction, PFCH4[NMC-FID], as follows:

(1) Select CH4 and C2H6 analytical gas mixtures and ensure that both mixtures meet the specifications of § 1065.750. Select a CH4 concentration that you would use for spanning the FID during emission testing and select a C2H6 concentration that is typical of the peak NMHC concentration expected at the hydrocarbon standard or equal to the THC analyzer's span value. For CH4 analyzers with multiple ranges, perform this procedure on the highest range used for emission testing.

(2) Start and operate the nonmethane cutter according to the manufacturer's instructions, including any temperature optimization.

(3) Confirm that the FID analyzer meets all the specifications of § 1065.360.

(4) Start and operate the FID analyzer according to the manufacturer's instructions.

(5) Zero and span the FID as you would during emission testing. Span the FID by bypassing the cutter and by using CH4 span gas. Note that you must span the FID on a C1 basis. For example, if your span gas has a methane reference value of 100 µmol/mol, the correct FID response to that span gas is 100 µmol/mol because there is one carbon atom per CH4 molecule.

(6) Introduce the C2H6 analytical gas mixture upstream of the nonmethane cutter. Use good engineering judgment to address the effect of hydrocarbon contamination if your point of introduction is vastly different from the point of zero/span gas introduction.

(7) Allow time for the analyzer response to stabilize. Stabilization time may include time to purge the nonmethane cutter and to account for the analyzer's response.

(8) While the analyzer measures a stable concentration, record 30 seconds of sampled data. Calculate the arithmetic mean of these data points.

(9) Divide the mean C2H6 concentration by the reference concentration of C2H6, converted to a C1 basis. The result is the combined C2H6 response factor and C2H6 penetration fraction, RFPFC2H6[NMC-FID]. Use this combined C2H6 response factor and C2H6 penetration fraction according to § 1065.660(b)(2)(iii) or (d)(1)(iii) or § 1065.665, as applicable.

(10) Introduce the CH4 analytical gas mixture upstream of the nonmethane cutter. Use good engineering judgment to address the effect of hydrocarbon contamination if your point of introduction is vastly different from the point of zero/span gas introduction.

(11) Allow time for the analyzer response to stabilize. Stabilization time may include time to purge the nonmethane cutter and to account for the analyzer's response.

(12) While the analyzer measures a stable concentration, record 30 seconds of sampled data. Calculate the arithmetic mean of these data points.

(13) Reroute the flow path to bypass the nonmethane cutter, introduce the CH4 analytical gas mixture, and repeat the steps in paragraphs (e)(11) and (12) of this section.

(14) Divide the mean CH4 concentration measured through the nonmethane cutter by the mean CH4 concentration measured after bypassing the nonmethane cutter. The result is the CH4 penetration fraction, PFCH4[NMC-FID]. Use this CH4 penetration fraction according to § 1065.660(b)(2)(iii) or (d)(1)(iii) or § 1065.665, as applicable.

(a) Scope and frequency. If you measure CH4, C2H6, NMHC, or NMNEHC using an FTIR analyzer, verify the amount of interference after initial analyzer installation and after major maintenance.

(b) Measurement principles. Interference gases can interfere with certain analyzers by causing a response similar to the target analyte. If the analyzer uses compensation algorithms that utilize measurements of other gases to meet this interference verification, simultaneously conduct these other measurements to test the compensation algorithms during the analyzer interference verification.

(c) System requirements. An FTIR analyzer must have combined interference that is within ±2% of the flow-weighted mean concentration of CH4, NMHC, or NMNEHC expected at the standard, though we strongly recommend a lower interference that is within ±1%.

(d) Procedure. Perform the interference verification for an FTIR analyzer using the same procedure that applies for N2O analyzers in § 1065.375(d).

(a) Scope and frequency. If you measure ethanol or methanol using a photoacoustic analyzer, verify the amount of H2O, CO, and CO2 interference after initial analyzer installation and after major maintenance.

(b) Measurement principles. H2O, CO, and CO2 can positively interfere with a photoacoustic analyzer by causing a response similar to ethanol or methanol. If the photoacoustic analyzer uses compensation algorithms that utilize measurements of other gases to meet this interference verification, simultaneously conduct these other measurements to test the compensation algorithms during the analyzer interference verification.

(c) System requirements. Photoacoustic analyzers must have combined interference that is within (0.0 ±0.5) µmol/mol. We strongly recommend a lower interference that is within (0.0 ±0.25) µmol/mol.

(d) Procedure. Perform the interference verification by following the procedure in § 1065.375(d), comparing the results to paragraph (c) of this section.

(a) Scope and frequency. If you use a CLD analyzer to measure NOX, verify the amount of H2O and CO2 quench after installing the CLD analyzer and after major maintenance.

(b) Measurement principles. H2O and CO2 can negatively interfere with a CLD's NOX response by collisional quenching, which inhibits the chemiluminescent reaction that a CLD utilizes to detect NOX. This procedure and the calculations in § 1065.675 determine quench and scale the quench results to the maximum mole fraction of H2O and the maximum CO2 concentration expected during emission testing. If the CLD analyzer uses quench compensation algorithms that utilize H2O and/or CO2 measurement instruments, evaluate quench with these instruments active and evaluate quench with the compensation algorithms applied.

(c) System requirements. A CLD analyzer must have a combined H2O and CO2 quench of ±2% or less, though we strongly recommend a quench of ±1% or less. Combined quench is the sum of the CO2 quench determined as described in paragraph (d) of this section, plus the H2O quench determined in paragraph (e) of this section.

(d) CO2 quench verification procedure. Use the following method to determine CO2 quench by using a gas divider that blends binary span gases with zero gas as the diluent and meets the specifications in § 1065.248, or use good engineering judgment to develop a different protocol:

(1) Use PTFE or stainless steel tubing to make necessary connections.

(2) Configure the gas divider such that nearly equal amounts of the span and diluent gases are blended with each other.

(3) If the CLD analyzer has an operating mode in which it detects NO-only, as opposed to total NOX, operate the CLD analyzer in the NO-only operating mode.

(4) Use a CO2 span gas that meets the specifications of § 1065.750 and a concentration that is approximately twice the maximum CO2 concentration expected during emission testing.

(5) Use an NO span gas that meets the specifications of § 1065.750 and a concentration that is approximately twice the maximum NO concentration expected during emission testing.

(6) Zero and span the CLD analyzer. Span the CLD analyzer with the NO span gas from paragraph (d)(5) of this section through the gas divider. Connect the NO span gas to the span port of the gas divider; connect a zero gas to the diluent port of the gas divider; use the same nominal blend ratio selected in paragraph (d)(2) of this section; and use the gas divider's output concentration of NO to span the CLD analyzer. Apply gas property corrections as necessary to ensure accurate gas division.

(7) Connect the CO2 span gas to the span port of the gas divider.

(8) Connect the NO span gas to the diluent port of the gas divider.

(9) While flowing NO and CO2 through the gas divider, stabilize the output of the gas divider. Determine the CO2 concentration from the gas divider output, applying gas property correction as necessary to ensure accurate gas division, or measure it using an NDIR. Record this concentration, xCO2act, and use it in the quench verification calculations in § 1065.675. Alternatively, you may use a simple gas blending device and use an NDIR to determine this CO2 concentration. If you use an NDIR, it must meet the requirements of this part for laboratory testing and you must span it with the CO2 span gas from paragraph (d)(4) of this section.

(10) Measure the NO concentration downstream of the gas divider with the CLD analyzer. Allow time for the analyzer response to stabilize. Stabilization time may include time to purge the transfer line and to account for analyzer response. While the analyzer measures the sample's concentration, record the analyzer's output for 30 seconds. Calculate the arithmetic mean concentration from these data, xNOmeas. Record xNOmeas, and use it in the quench verification calculations in § 1065.675.

(11) Calculate the actual NO concentration at the gas divider's outlet, xNOact, based on the span gas concentrations and xCO2act according to Eq. 1065.675-2. Use the calculated value in the quench verification calculations in Eq. 1065.675-1.

(12) Use the values recorded according to this paragraph (d) and paragraph (e) of this section to calculate quench as described in § 1065.675.

(e) H2O quench verification procedure. Use the following method to determine H2O quench, or use good engineering judgment to develop a different protocol:

(1) Use PTFE or stainless steel tubing to make necessary connections.

(2) If the CLD analyzer has an operating mode in which it detects NO-only, as opposed to total NOX, operate the CLD analyzer in the NO-only operating mode.

(3) Use an NO span gas that meets the specifications of § 1065.750 and a concentration that is near the maximum concentration expected during emission testing.

(4) Zero and span the CLD analyzer. Span the CLD analyzer with the NO span gas from paragraph (e)(3) of this section, record the span gas concentration as xNOdry, and use it in the quench verification calculations in § 1065.675.

(5) Create a humidified NO span gas by bubbling a NO gas that meets the specifications in § 1065.750 through distilled H2O in a sealed vessel or use a device that introduces distilled H2O as vapor into a controlled gas flow. If the sample does not pass through a dryer during emission testing, humidify your test gas to an H2O level approximately equal to the maximum mole fraction of H2O expected during emission testing. If the humidified NO span gas sample does not pass through a sample dryer, the quench verification calculations in § 1065.675 scale the measured H2O quench to the highest mole fraction of H2O expected during emission testing. If the sample passes through a dryer during emission testing, you must humidify your test gas to an H2O level at or above the level determined in § 1065.145(e)(2) for that dryer. For this case, the quench verification calculations in § 1065.675 do not scale the measured H2O quench.

(6) Introduce the humidified NO test gas into the sample system. You may introduce it upstream or downstream of any sample dryer that is used during emission testing. Note that the sample dryer must meet the sample dryer verification check in § 1065.342.

(7) Measure the mole fraction of H2O in the humidified NO span gas downstream of the sample dryer, xH2Omeas. We recommend that you measure xH2Omeas as close as possible to the CLD analyzer inlet. You may calculate xH2Omeas from measurements of dew point, Tdew, and absolute pressure, ptotal.

(8) Use good engineering judgment to prevent condensation in the transfer lines, fittings, or valves from the point where xH2Omeas is measured to the analyzer. We recommend that you design your system so the wall temperatures in the transfer lines, fittings, and valves from the point where xH2Omeas is measured to the analyzer are at least 5 °C above the local sample gas dew point.

(9) Measure the humidified NO span gas concentration with the CLD analyzer. Allow time for the analyzer response to stabilize. Stabilization time may include time to purge the transfer line and to account for analyzer response. While the analyzer measures the sample's concentration, record the analyzer's output for 30 seconds. Calculate the arithmetic mean of these data, xNOwet. Record xNOwet and use it in the quench verification calculations in § 1065.675.

(f) Corrective action. If the sum of the H2O quench plus the CO2 quench is less than −2% or greater than + 2%, take corrective action by repairing or replacing the analyzer. Before running emission tests, verify that the corrective action successfully restored the analyzer to proper functioning.

(g) Exceptions. The following exceptions apply:

(1) You may omit this verification if you can show by engineering analysis that for your NOX sampling system and your emission calculation procedures, the combined CO2 and H2O interference for your NOX CLD analyzer always affects your brake-specific NOX emission results within no more than ±1% of the applicable NOX standard. If you certify to a combined emission standard (such as a NOX + NMHC standard), scale your NOX results to the combined standard based on the measured results (after incorporating deterioration factors, if applicable). For example, if your final NOX + NMHC value is half of the emission standard, double the NOX result to estimate the level of NOX emissions corresponding to the applicable standard.

(2) You may use a NOX CLD analyzer that you determine does not meet this verification, as long as you try to correct the problem and the measurement deficiency does not adversely affect your ability to show that engines comply with all applicable emission standards.

(a) Scope and frequency. If you measure NOX using an NDUV analyzer, verify the amount of H2O and hydrocarbon interference after initial analyzer installation and after major maintenance.

(b) Measurement principles. Hydrocarbons and H2O can positively interfere with an NDUV analyzer by causing a response similar to NOX. If the NDUV analyzer uses compensation algorithms that utilize measurements of other gases to meet this interference verification, simultaneously conduct such measurements to test the algorithms during the analyzer interference verification.

(c) System requirements. A NOX NDUV analyzer must have combined H2O and HC interference within ±2% of the flow-weighted mean concentration of NOX expected at the standard, though we strongly recommend keeping interference within ±1%.

(d) Procedure. Perform the interference verification as follows:

(1) Start, operate, zero, and span the NOX NDUV analyzer according to the instrument manufacturer's instructions.

(2) We recommend that you extract engine exhaust to perform this verification. Use a CLD that meets the specifications of subpart C of this part to quantify NOX in the exhaust. Use the CLD response as the reference value. Also measure HC in the exhaust with a FID analyzer that meets the specifications of subpart C of this part. Use the FID response as the reference hydrocarbon value.

(3) Upstream of any sample dryer, if one is used during testing, introduce the engine exhaust to the NDUV analyzer.

(4) Allow time for the analyzer response to stabilize. Stabilization time may include time to purge the transfer line and to account for analyzer response.

(5) While all analyzers measure the sample's concentration, record 30 seconds of sampled data, and calculate the arithmetic means for the three analyzers.

(6) Subtract the CLD mean from the NDUV mean.

(7) Multiply this difference by the ratio of the flow-weighted mean HC concentration expected at the standard to the HC concentration measured during the verification. The analyzer meets the interference verification of this section if this result is within ±2% of the NOX concentration expected at the standard.

(e) Exceptions. The following exceptions apply:

(1) You may omit this verification if you can show by engineering analysis that for your NOX sampling system and your emission calculation procedures, the combined HC and H2O interference for your NOX NDUV analyzer always affects your brake-specific NOX emission results by less than 0.5% of the applicable NOX standard.

(a) Scope and frequency. See § 1065.275 to determine whether you need to verify the amount of interference after initial analyzer installation and after major maintenance.

(b) Measurement principles. Interference gases can positively interfere with certain analyzers by causing a response similar to N2O. If the analyzer uses compensation algorithms that utilize measurements of other gases to meet this interference verification, simultaneously conduct these other measurements to test the compensation algorithms during the analyzer interference verification.

(c) System requirements. Analyzers must have combined interference that is within (0.0 ±1.0) µmol/mol. We strongly recommend a lower interference that is within (0.0 ±0.5) µmol/mol.

(d) Procedure. Perform the interference verification as follows:

(1) Start, operate, zero, and span the N2O analyzer as you would before an emission test. If the sample is passed through a dryer during emission testing, you may run this verification test with the dryer if it meets the requirements of § 1065.342. Operate the dryer at the same conditions as you will for an emission test. You may also run this verification test without the sample dryer.

(2) Create a humidified test gas by bubbling a multi component span gas that incorporates the target interference species and meets the specifications in § 1065.750 through distilled H2O in a sealed vessel or use a device that introduces distilled H2O as vapor into a controlled gas flow. If the sample does not pass through a dryer during emission testing, humidify your test gas to an H2O level at or above the maximum expected during emission testing. If the sample passes through a dryer during emission testing, you must humidify your test gas to an H2O level at or above the level determined in § 1065.145(e)(2) for that dryer. Use interference span gas concentrations that are at least as high as the maximum expected during testing.

(3) Introduce the humidified interference test gas into the sample system. You may introduce it downstream of any sample dryer, if one is used during testing.

(4) If the sample is not passed through a dryer during this verification test, measure the H2O mole fraction, xH2O, of the humidified interference test gas as close as possible to the inlet of the analyzer. For example, measure dewpoint, Tdew, and absolute pressure, ptotal, to calculate xH2O. Verify that the H2O content meets the requirement in paragraph (d)(2) of this section. If the sample is passed through a dryer during this verification test, you must verify that the H2O content of the humidified test gas downstream of the vessel meets the requirement in paragraph (d)(2) of this section based on either direct measurement of the H2O content (e.g., dewpoint and pressure) or an estimate based on the vessel pressure and temperature. Use good engineering judgment to estimate the H2O content. For example, you may use previous direct measurements of H2O content to verify the vessel's level of saturation.

(5) If a sample dryer is not used in this verification test, use good engineering judgment to prevent condensation in the transfer lines, fittings, or valves from the point where xH2O is measured to the analyzer. We recommend that you design your system so that the wall temperatures in the transfer lines, fittings, and valves from the point where xH2O is measured to the analyzer are at least 5 ºC above the local sample gas dewpoint.

(6) Allow time for the analyzer response to stabilize. Stabilization time may include time to purge the transfer line and to account for analyzer response.

(7) While the analyzer measures the sample's concentration, record its output for 30 seconds. Calculate the arithmetic mean of this data. When performed with all the gases simultaneously, this is the combined interference.

(8) The analyzer meets the interference verification if the result of paragraph (d)(7) of this section meets the tolerance in paragraph (c) of this section.

(9) You may also run interference procedures separately for individual interference gases. If the interference gas levels used are higher than the maximum levels expected during testing, you may scale down each observed interference value (the arithmetic mean of 30 second data described in paragraph (d)(7) of this section) by multiplying the observed interference by the ratio of the maximum expected concentration value to the actual value used during this procedure. You may run separate interference concentrations of H2O (down to 0.025 mol/mol H2O content) that are lower than the maximum levels expected during testing, but you must scale up the observed H2O interference by multiplying the observed interference by the ratio of the maximum expected H2O concentration value to the actual value used during this procedure. The sum of the scaled interference values must meet the tolerance for combined interference as specified in paragraph (c) of this section.

(a) Scope and frequency. If you use a chiller to dry a sample upstream of a NOX measurement instrument, but you don't use an NO2-to-NO converter upstream of the chiller, you must perform this verification for chiller NO2 penetration. Perform this verification after initial installation and after major maintenance.

(b) Measurement principles. A chiller removes H2O, which can otherwise interfere with a NOX measurement. However, liquid H2O remaining in an improperly designed chiller can remove NO2 from the sample. If a chiller is used without an NO2-to-NO converter upstream, it could remove NO2 from the sample prior NOX measurement.

(c) System requirements. A chiller must allow for measuring at least 95% of the total NO2 at the maximum expected concentration of NO2.

(d) Procedure. Use the following procedure to verify chiller performance:

(1) Instrument setup. Follow the analyzer and chiller manufacturers' start-up and operating instructions. Adjust the analyzer and chiller as needed to optimize performance.

(2) Equipment setup and data collection. (i) Zero and span the total NOX gas analyzer(s) as you would before emission testing.

(ii) Select an NO2 calibration gas, balance gas of dry air, that has an NO2 concentration within ±5% of the maximum NO2 concentration expected during testing.

(iii) Overflow this calibration gas at the gas sampling system's probe or overflow fitting. Allow for stabilization of the total NOX response, accounting only for transport delays and instrument response.

(iv) Calculate the mean of 30 seconds of recorded total NOX data and record this value as xNOXref.

(v) Stop flowing the NO2 calibration gas.

(vi) Next saturate the sampling system by overflowing a dewpoint generator's output, set at a dewpoint of 50 °C, to the gas sampling system's probe or overflow fitting. Sample the dewpoint generator's output through the sampling system and chiller for at least 10 minutes until the chiller is expected to be removing a constant rate of H2O.

(vii) Immediately switch back to overflowing the NO2 calibration gas used to establish xNOxref. Allow for stabilization of the total NOX response, accounting only for transport delays and instrument response. Calculate the mean of 30 seconds of recorded total NOX data and record this value as xNOxmeas.

(viii) Correct xNOxmeas to xNOxdry based upon the residual H2O vapor that passed through the chiller at the chiller's outlet temperature and pressure.

(3) Performance evaluation. If xNOxdry is less than 95% of xNOxref, repair or replace the chiller.

(e) Exceptions. The following exceptions apply:

(1) You may omit this verification if you can show by engineering analysis that for your NOX sampling system and your emission calculations procedures, the chiller always affects your brake-specific NOX emission results by less than 0.5% of the applicable NOX standard.

(2) You may use a chiller that you determine does not meet this verification, as long as you try to correct the problem and the measurement deficiency does not adversely affect your ability to show that engines comply with all applicable emission standards.

(a) Scope and frequency. If you use an analyzer that measures only NO to determine NOX, you must use an NO2-to-NO converter upstream of the analyzer. Perform this verification after installing the converter, after major maintenance and within 35 days before an emission test. This verification must be repeated at this frequency to verify that the catalytic activity of the NO2-to-NO converter has not deteriorated.

(b) Measurement principles. An NO2-to-NO converter allows an analyzer that measures only NO to determine total NOX by converting the NO2 in exhaust to NO.

(c) System requirements. An NO2-to-NO converter must allow for measuring at least 95% of the total NO2 at the maximum expected concentration of NO2.

(d) Procedure. Use the following procedure to verify the performance of a NO2-to-NO converter:

(1) Instrument setup. Follow the analyzer and NO2-to-NO converter manufacturers' start-up and operating instructions. Adjust the analyzer and converter as needed to optimize performance.

(2) Equipment setup. Connect an ozonator's inlet to a zero-air or oxygen source and connect its outlet to one port of a three-way tee fitting. Connect an NO span gas to another port, and connect the NO2-to-NO converter inlet to the last port.

(3) Adjustments and data collection. Perform this check as follows:

(i) Set ozonator air off, turn ozonator power off, and set the analyzer to NO mode. Allow for stabilization, accounting only for transport delays and instrument response.

(ii) Use an NO concentration that is representative of the peak total NOX concentration expected during testing. The NO2 content of the gas mixture shall be less than 5% of the NO concentration. Record the concentration of NO by calculating the mean of 30 seconds of sampled data from the analyzer and record this value as xNOref.

(iii) Turn on the ozonator O2 supply and adjust the O2 flow rate so the NO indicated by the analyzer is about 10 percent less than xNOref. Record the concentration of NO by calculating the mean of 30 seconds of sampled data from the analyzer and record this value as xNO + O2mix.

(iv) Switch the ozonator on and adjust the ozone generation rate so the NO measured by the analyzer is 20 percent of xNOref or a value which would simulate the maximum concentration of NO2 expected during testing, while maintaining at least 10 percent unreacted NO. This ensures that the ozonator is generating NO2 at the maximum concentration expected during testing. Record the concentration of NO by calculating the mean of 30 seconds of sampled data from the analyzer and record this value as xNOmeas.

(v) Switch the NOX analyzer to NOX mode and measure total NOX. Record the concentration of NOX by calculating the mean of 30 seconds of sampled data from the analyzer and record this value as xNOxmeas.

(vi) Switch off the ozonator but maintain gas flow through the system. The NOX analyzer will indicate the NOX in the NO + O2 mixture. Record the concentration of NOX by calculating the mean of 30 seconds of sampled data from the analyzer and record this value as xNOx + O2mix.

(vii) Turn off the ozonator O2 supply. The NOX analyzer will indicate the NOX in the original NO-in-N2 mixture. Record the concentration of NOX by calculating the mean of 30 seconds of sampled data from the analyzer and record this value as xNOxref. This value should be no more than 5 percent above the xNOref value.

(4) Performance evaluation. Calculate the efficiency of the NOX converter by substituting the concentrations obtained into the following equation:

(5) If the result is less than 95%, repair or replace the NO2-to-NO converter.

(e) Exceptions. The following exceptions apply:

(1) You may omit this verification if you can show by engineering analysis that for your NOX sampling system and your emission calculations procedures, the converter always affects your brake-specific NOX emission results by less than 0.5% of the applicable NOX standard.

(a) Scope and frequency. This section describes three verifications.

(1) Independent verification of PM balance performance within 370 days before weighing any filter.

(2) Zero and span the balance within 12 h before weighing any filter.

(3) Verify that the mass determination of reference filters before and after a filter weighing session are less than a specified tolerance.

(b) Independent verification. Have the balance manufacturer (or a representative approved by the balance manufacturer) verify the balance performance within 370 days of testing. Balances have internal weights that compensate for drift due to environmental changes. These internal weights must be verified as part of this independent verification with external, certified calibration weights that meet the specifications in § 1065.790.

(c) Zeroing and spanning. You must verify balance performance by zeroing and spanning it with at least one calibration weight. Also, any external weights you use must meet the specifications in § 1065.790. Any weights internal to the PM balance used for this verification must be verified as described in paragraph (b) of this section.

(1) Use a manual procedure in which you zero the balance and span the balance with at least one calibration weight. If you normally use mean values by repeating the weighing process to improve the accuracy and precision of PM measurements, use the same process to verify balance performance.

(2) You may use an automated procedure to verify balance performance. For example most balances have internal weights for automatically verifying balance performance.

(d) Reference sample weighing. Verify all mass readings during a weighing session by weighing reference PM sample media (e.g., filters) before and after a weighing session. A weighing session may be as short as desired, but no longer than 80 hours, and may include both pre-test and post-test mass readings. We recommend that weighing sessions be eight hours or less. Successive mass determinations of each reference PM sample media (e.g., filter) must return the same value within ±10 µg or ±10% of the net PM mass expected at the standard (if known), whichever is higher. If successive reference PM sample media (e.g., filter) weighing events fail this criterion, invalidate all individual test media (e.g., filter) mass readings occurring between the successive reference media (e.g., filter) mass determinations. You may reweigh these media (e.g., filter) in another weighing session. If you invalidate a pre-test media (e.g., filter) mass determination, that test interval is void. Perform this verification as follows:

(1) Keep at least two samples of unused PM sample media (e.g., filters) in the PM-stabilization environment. Use these as references. If you collect PM with filters, select unused filters of the same material and size for use as references. You may periodically replace references, using good engineering judgment.

(2) Stabilize references in the PM stabilization environment. Consider references stabilized if they have been in the PM-stabilization environment for a minimum of 30 min, and the PM-stabilization environment has been within the specifications of § 1065.190(d) for at least the preceding 60 min.

(3) Exercise the balance several times with a reference sample. We recommend weighing ten samples without recording the values.

(4) Zero and span the balance. Using good engineering judgment, place a test mass such as a calibration weight on the balance, then remove it. After spanning, confirm that the balance returns to a zero reading within the normal stabilization time.

(5) Weigh each of the reference media (e.g., filters) and record their masses. We recommend using substitution weighing as described in § 1065.590(j). If you normally use mean values by repeating the weighing process to improve the accuracy and precision of the reference media (e.g., filter) mass, you must use mean values of sample media (e.g., filter) masses.

(6) Record the balance environment dewpoint, ambient temperature, and atmospheric pressure.

(7) Use the recorded ambient conditions to correct results for buoyancy as described in § 1065.690. Record the buoyancy-corrected mass of each of the references.

(8) Subtract each reference media's (e.g., filter's) buoyancy-corrected reference mass from its previously measured and recorded buoyancy-corrected mass.

(9) If any of the reference filters' observed mass changes by more than that allowed under this paragraph, you must invalidate all PM mass determinations made since the last successful reference media (e.g. filter) mass validation. You may discard reference PM media (e.g. filters) if only one of the filter's mass changes by more than the allowable amount and you can positively identify a special cause for that filter's mass change that would not have affected other in-process filters. Thus, the validation can be considered a success. In this case, you do not have to include the contaminated reference media when determining compliance with paragraph (d)(10) of this section, but the affected reference filter must be immediately discarded and replaced prior to the next weighing session.

(10) If any of the reference masses change by more than that allowed under this paragraph (d), invalidate all PM results that were determined between the two times that the reference masses were determined. If you discarded reference PM sample media according to paragraph (d)(9) of this section, you must still have at least one reference mass difference that meets the criteria in this paragraph (d). Otherwise, you must invalidate all PM results that were determined between the two times that the reference media (e.g., filters) masses were determined.

This section describes how to verify the performance of an inertial PM balance.

(a) Independent verification. Have the balance manufacturer (or a representative approved by the balance manufacturer) verify the inertial balance performance within 370 days before testing.

(b) Other verifications. Perform other verifications using good engineering judgment and instrument manufacturer recommendations.