91.413 Exhaust sample procedure - gaseous components.§ 91.413 Exhaust sample procedure - gaseous components.
(a) Automatic data collection equipment requirements. The analyzer response may be read by automatic data collection (ADC) equipment such as computers, data loggers, etc. If ADC equipment is used the following is required:
(1) For dilute grab (“bag”) analysis, the analyzer response must be stable at greater than 99 percent of the final reading for the dilute exhaust sample bag. A single value representing the average chart deflection over a 10-second stabilized period shall be stored.
(2) For continuous analysis systems, a single value representing the average integrated concentration over a cycle shall be stored. Alternatively, the ADC may store the individual instantaneous values collected during the measurement period.
(3) The chart deflections or average integrated concentrations required in paragraphs (a)(1) and (a)(2) of this section may be stored on long-term computer storage devices such as computer tapes, storage discs, punch cards, and so forth, or they may be printed in a listing for storage. In either case a chart recorder is not required and records from a chart recorder, if they exist, need not be stored.
(4) If ADC equipment is used to interpret analyzer values, the ADC equipment is subject to the calibration specifications of the analyzer as if the ADC equipment is part of analyzer system.
(b) Data records from any one or a combination of analyzers may be stored as chart recorder records.
(c) Grab sample analysis. For dilute grab sample analysis perform the following sequence:
(1) Calibrate analyzers using the procedure described in § 91.326.
(2) Record the most recent zero and span response as the pre-analysis value.
(3) Measure HC, CO, CO2, and NOX background concentrations in the sample bag(s) and background sample bag(s) using the same flow rates and pressures.
(4) Good engineering practice dictates that analyzers used for continuous analysis should be operated such that the measured concentration falls between 15 percent and 100 percent of full scale.
(5) A post-analysis zero and span check of each range must be performed and the values recorded. The number of events that may occur between the pre and post checks is not specified. However, the difference between pre-analysis zero and span values (recorded in paragraph (c)(5) or (c)(6) of this section) versus those recorded for the post-analysis check may not exceed the zero drift limit or the span drift limit of 2 percent of full scale chart deflection for any range used. Otherwise the test is void.
(d) Continuous sample analysis. For continuous sample analysis, perform the following sequence:
(1) Calibrate analyzers using the procedures described in § 91.326.
(2) Leak check portions of the sampling system that operate at negative gauge pressures when sampling, and allow heated sample lines, filters, pumps, and so forth to stabilize at operating temperature.
(3) Option: Determine the hang-up for the FID or HFID sampling system:
(i) Zero the analyzer using zero air introduced at the analyzer port.
(ii) Flow zero air through the overflow sampling system. Check the analyzer response.
(iii) If the overflow zero response exceeds the analyzer zero response by two percent or more of the FID or HFID full-scale deflection, hang-up is indicated and corrective action must be taken (see paragraph (e) of this section).
(iv) The complete system hang-up check specified in paragraph (f) of this section is recommended as a periodic check.
(4) Obtain a stable zero reading.
(5) Good engineering practice dictates that analyzers used for continuous analysis should be operated such that the measured concentration falls between 15 percent and 100 percent of full scale.
(6) Record the most recent zero and span response as the pre-analysis values.
(7) Collect background HC, CO, CO2, and NOX in a sample bag (for dilute exhaust sampling only, see § 91.422).
(8) Perform a post-analysis zero and span check for each range used at the conditions specified in paragraph (d)(1) of this section. Record these responses as the post-analysis values.
(9) Neither the zero drift nor the span drift between the pre-analysis and post-analysis checks on any range used may exceed three percent for HC, or two percent for NOX. CO, and CO2, of full scale chart deflection, or the test is void. (If the HC drift is greater than three percent of full-scale chart deflection, hydrocarbon hang-up is likely.)
(10) Determine background levels of NOX. CO, or CO2 (for dilute exhaust sampling only) by the grab (“bag”) technique outlined in paragraph (c) of this section.
(e) Hydrocarbon hang-up. If HC hang-up is indicated, the following sequence may be performed:
(1) Fill a clean sample bag with background air.
(2) Zero and span the HFID at the analyzer ports.
(3) Analyze the background air sample bag through the analyzer ports.
(4) Analyze the background air through the entire sample probe system.
(5) If the difference between the readings obtained is two ppm or more, clean the sample probe and the sample line.
(6) Reassemble the sample system, heat to specified temperature, and repeat the procedure in paragraphs (e)(1) through (e)(5) of this section.