40 CFR § 86.540-90 - Exhaust sample analysis.
The following sequence of operations shall be performed in conjunction with each series of measurements:
(1) Zero the analyzers and obtain a stable zero reading. Recheck after tests.
(2) Introduce span gases and set instrument gains. In order to avoid errors, span and calibrate at the same flow rates used to analyze the test sample. Span gases should have concentrations equal to 75 to 100 percent of full scale. If gain has shifted significantly on the analyzers, check the calibrations. Show actual concentrations on chart.
(3) Check zeros; repeat the procedure in paragraphs (a) (1) and (2) of this section if required.
(4) Check flow rates and pressures.
(5) Measure HC, CO, CO2, and, if appropriate, NOX. concentrations of samples.
(6) Check zero and span points. If difference is greater than 2 percent of full scale, repeat the procedure in paragraphs (a) (1) through (5) of this section.
(c) For HCHO (methanol-fueled vehicles), introduce test samples into the high pressure liquid chromatograph and measure the concentration of formaldehyde as a dinitropheylhydrazine derivative in acetonitrile. This concentration is CFS in the calculations.