40 CFR 90.320 - Carbon dioxide analyzer calibration.
(a) Prior to its initial use and monthly thereafter, or within one month prior to the certification test, calibrate the NDIR carbon dioxide analyzer as follows:
(1) Follow good engineering practices for instrument start-up and operation. Adjust the analyzer to optimize performance.
(2) Zero the carbon dioxide analyzer with either purified synthetic air or zero-grade nitrogen.
(3) Calibrate on each normally used operating range with carbon dioxide-in-N2 calibration or span gases having nominal concentrations between 10 and 90 percent of that range. A minimum of six evenly spaced points covering at least 80 percent of the 10 to 90 range (64 percent) is required (see following table).
|Example calibration points (%)||Acceptable for Calibration?|
|20, 30, 40, 50, 60, 70||No, range covered is 50 percent, not 64.|
|20, 30, 40, 50, 60, 70, 80, 90||Yes.|
|10, 25, 40, 55, 70, 85||Yes.|
|10, 30, 50, 70, 90||No, though equally spaced and entire range covered, a minimum of six points are needed.|
(b) The initial and periodic interference, system check, and calibration test procedures specified in 40 CFR part 1065, subparts C and D, may be used in lieu of the procedures in this section.