86.1323-84—Oxides of nitrogen analyzer calibration.
The chemiluminescent oxides of nitrogen analyzer shall receive the following initial and periodic calibration.
(a)
Prior to introduction into service and at least monthly thereafter, the chemiluminescent oxides of nitrogen analyzer must be checked for NO2 to NO converter efficiency. Figure N84-9 is a reference for paragraphs (a) (1) through (11) of this section.
(1)
Follow good engineering practices for instrument start-up and operation. Adjust the analyzer to optimize performance.
(3)
Connect the outlet of the NOX generator to the sample inlet of the oxides of nitrogen analyzer which has been set to the most common operating range.
(4)
Introduce into the NOX generator analyzer-system an NO-in-nitrogen (N2) mixture with an NO concentration equal to approximately 80 percent of the most common operating range. The NO2 content of the gas mixture shall be less than 5 percent of the NO concentration.
Code of Federal Regulations
(5)
With the oxides of nitrogen analyzer in the NO mode, record the concentration of NO indicated by the analyzer.
(6)
Turn on the NOX generator O2 (or air) supply and adjust the O2 (or air) flow rate so that the NO indicated by the analyzer is about 10 percent less than indicated in paragraph (a)(5) of this section. Record the concentration of NO in this NO O2 mixture.
(7)
Switch the NOX generator to the generation mode and adjust the generation rate so that the NO measured on the analyzer is 20 percent of that measured in paragraph (a)(5) of this section. There must be at least 10 percent unreacted NO at this point. Record the concentration of residual NO.
(8)
Switch the oxides of nitrogen analyzer to the NOX mode and measure total NOX. Record this value.
(9)
Switch off the NOX generator but maintain gas flow through the system. The oxides of nitrogen analyzer will indicate the NOX in the NO O2 mixture. Record this value.
(10)
Turn off the NOX generator O2 (or air) supply. The analyzer will now indicate the NOX in the original NO-in-N2 mixture. This value should be no more than 5 percent above the value indicated in paragraph (a)(4) of this section.
(11)
Calculate the efficiency of the NOX converter by substituting the concentrations obtained into the following equation:
Where:
a = concentration obtained in paragraph (a)(8),
b = concentration obtained in paragraph (a)(9),
c = concentration obtained in paragraph (a)(6),
d = concentration obtained in paragraph (a)(7).
If converter efficiency is not greater than 90 percent corrective action will be required.
(b) Initial and periodic calibration.
Prior to its introduction into service and monthly thereafter, the chemiluminescent oxides of nitrogen analyzer shall be calibrated on all normally used instrument ranges. Use the same flow rate as when analyzing samples. Proceed as follows:
(3)
Calibrate on each used operating range with a minimum of 6, approximately equally spaced, NO-in-N2 calibration gases (e.g., 15, 30, 45, 60, 75, and 90 percent of that range). For each range calibrated, if the deviation from a least-squares best-fit straight line is within ±2 percent of the value at each non-zero data point and within ±0.3 percent of full scale on the zero data point, then concentration values may be calculated using the linear calibration equation for that range. If the deviation exceeds these limits, then the best-fit non-linear equation which represents the data within these limits shall be used to determine concentration values.
(c)
The initial and periodic interference, system check, and calibration test procedures specified in 40 CFR part 86, subpart D, may be used in lieu of the procedures specified in this section.
(d)
When testing methanol-fueled engines it may be necessary to clean the analyzer frequently to prevent interference with NOX measurements (see EPA/60/S3-88/040).