1065.550—Gas analyzer range validation, drift validation, and drift correction.
(a) Range validation.
If an analyzer operated above 100% of its range at any time during the test, perform the following steps:
(1)
For batch sampling, re-analyze the sample using the lowest analyzer range that results in a maximum instrument response below 100%. Report the result from the lowest range from which the analyzer operates below 100% of its range.
(2)
For continuous sampling, repeat the entire test using the next higher analyzer range. If the analyzer again operates above 100% of its range, repeat the test using the next higher range. Continue to repeat the test until the analyzer always operates at less than 100% of its range.
(b) Drift validation and drift correction.
Calculate two sets of brake-specific emission results for each test interval. Calculate one set using the data before drift correction and calculate the other set after correcting all the data for drift according to § 1065.672. Use the two sets of brake-specific emission results to validate the duty cycle for drift as follows:
(i)
For each test interval of the duty cycle and for each measured exhaust constituent, the difference between the uncorrected and the corrected brake-specific emission values over the test interval is within ±4% of the uncorrected value or applicable emission standard, whichever is greater. This requirement also applies for CO2, whether or not an emission standard applies for CO2. Where no emission standard applies for CO2, the difference must be within ±4% of the uncorrected value. See paragraph (b)(4) of this section for exhaust constituents other than CO2 for which no emission standard applies.
(ii)
For the entire duty cycle and for each measured exhaust constituent, the difference between the uncorrected and corrected composite brake-specific emission values over the entire duty cycle is within ± 4% of the uncorrected value or the applicable emission standard, whichever is greater. Note that for purposes of drift validation using composite brake-specific emission values over the entire duty cycle, leave unaltered any negative emission results over a given test interval (i.e., do not set them to zero). A third calculation of composite brake-specific emission values is required for final reporting. This calculation uses drift-corrected mass (or mass rate) values from each test interval and sets any negative mass (or mass rate) values to zero before calculating the composite brake-specific emission values over the entire duty cycle. This requirement also applies for CO2, whether or not an emission standard applies for CO2. Where no emission standard applies for CO2, the difference must be within ± 4% of the uncorrected value. See paragraph (b)(4) of this section for exhaust constituents other than CO2 for which no emission standard applies.
(2)
For standards consisting of combined, individual measurements of exhaust constituents (such as NOX NMHC or separate NO and NO2 measurements to comply with a NOX standard), the duty cycle shall be validated for drift if you satisfy one of the following:
(i)
For each test interval of the duty cycle and for each individually measured exhaust constituent (e.g. NO, NO2, NOX, or NMHC), the difference between the uncorrected and the corrected brake-specific emission values over the test interval is within ± 4% of the uncorrected value; or
(ii)
For each test interval of the duty cycle or for the entire duty cycle the difference between the combined (e.g. NOX NMHC) uncorrected and combined (e.g. NOX NMHC) corrected composite brake-specific emissions values over each test interval of the duty cycle or the entire duty cycle is within ± 4% of the uncorrected value or the applicable emissions standard, whichever is greater.
(3)
If the test is not validated for drift, you may consider the test results for the duty cycle to be valid only if, using good engineering judgment, the observed drift does not affect your ability to demonstrate compliance with the applicable emission standards. For example, if the drift-corrected value is less than the standard by at least two times the absolute difference between the uncorrected and corrected values, you may consider the data to be valid for demonstrating compliance with the applicable standard.
(4)
The provisions of this paragraph (b)(4) apply for measurement of pollutants other than CO2 for which no emission standard applies (for purposes of this provision, standards consisting of combined, individual measurements are considered to be standards for each individual pollutant). You may use measurements that do not meet the drift validation criteria specified in paragraph (b)(1). For example, this allowance may be appropriate for measuring and reporting very low concentrations of CH4 and N2 O as long as no emission standard applies for these compounds.