40 CFR § 1065.360 - FID optimization and verification.
(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) 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(g).
(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 (NMC), you may calibrate that FID using CH4 calibration gases with the NMC. 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, see § 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 CH4response 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 an NMC:
(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, RFCH4[THC-FID].
(12) You may determine the response factor as a function of molar water concentration using the following procedures and use this response factor to account for the CH4 response for NMHC determination described in § 1065.660(b)(2)(iii):
(i) Humidify the CH4 span gas as described in § 1065.365(g) and repeat the steps in paragraphs (d)(7) through (9) of this section until measurements are complete for each setpoint in the selected range.
(ii) 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].
(iii) 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.
(iv) Use this functional relationship to determine the response factor during an emission test.
(e) THC FID CH4response 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 RFCH4[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 RFCH4[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 RFCH4[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 RFCH4[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 RFCH4[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.