40 CFR 89.323 - NDIR analyzer calibration.
(a) Detector optimization. If necessary, follow the instrument manufacturer's instructions for initial start-up and basic operating adjustments.
(b) Calibration curve. Develop a calibration curve for each range used as follows:
(1) Zero the analyzer.
(2) Span the analyzer to give a response of approximately 90 percent of full-scale chart deflection.
(3) Recheck the zero response. If it has changed more than 0.5 percent of full scale, repeat the steps given in paragraphs (b)(1) and (b)(2) of this section.
(4) Record the response of calibration gases having nominal concentrations starting between 10 and 15 percent and increasing in at least six incremental steps to 90 percent of that range. The incremental steps are to be spaced to represent good engineering practice.
(5) Generate a calibration curve. The calibration curve shall be of fourth order or less, have five or fewer coefficients. If any range is within 2 percent of being linear a linear calibration may be used. Include zero as a data point. Compensation for known impurities in the zero gas can be made to the zero-data point. The calibration curve must fit the data points within 2 percent of point.
(6) Optional. A new calibration curve need not be generated if:
(i) A calibration curve conforming to paragraph (b)(5) of this section exists; or
(ii) The responses generated in paragraph (b)(4) of this section are within 1 percent of full scale or 2 percent of point, whichever is less, of the responses predicted by the calibration curve for the gases used in paragraph (b)(4) of this section.
(7) If multiple range analyzers are used, the lowest range used must meet the curve fit requirements below 15 percent of full scale.