(a) Prior to its introduction into service, 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 percent range (64 percent) is required (see following table).
| Example calibration points (percent) | Acceptable for calibration? |
|---|---|
| 20, 30, 40, 50, 60, 70 | No, range covered is 50 percent, not 64 percent. |
| 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 is needed. |
(4) Additional calibration points may be generated. For each range calibrated, if the deviation from a least-squares best-fit straight line is 2 percent or less of the value at each data point, concentration values may be calculated by use of a single calibration factor for that range. If the deviation exceeds 2 percent at any point, use the best-fit non-linear equation which represents the data to within 2 percent of each test point to determine concentration.
(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.
[61 FR 52102, Oct. 4, 1996, as amended at 70 FR 40451, July 13, 2005]
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