§ 86.332-79Oxides of nitrogen analyzer calibration.
(a) At least monthly during testing, perform a converter efficiency check as described in paragraph (b) of this section. Perform a monthly linearity check as described in paragraph (c) of this section.
(b)Converter-efficiency check. The apparatus described and illustrated in Figure D79-4 is to be used to determine the conversion efficiency of devices that convert NO2 to NO. The following procedure is to be used in determining the values to be used in the equation below:
(1) Follow the manufacturer's instructions for instrument startup and operation.
(2) Zero the oxides of nitrogen analyzer.
(3) Connect the outlet of the NOX generator (see Figure D79-4) 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 a span gas with a NO concentration equal to approximately 80 percent of the most common operating range.
(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 step (5). 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 step (5). 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 generation, but maintain gas flow through the system. The oxides of nitrogen analyzer will indicate the total 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 total NOX in the original NO in N2 mixture. This value should be no more than 5 percent above the value indicated in step (4).
(11) Calculate the efficiency of the NOX converter by substituting the concentrations obtained into the following equation:
Percent Efficiency = [1 (a − b)/(c − d)] × 100
a=concentration obtained in step (8).
b=concentration obtained in step (9).
c=concentration obtained in step (6).
d=concentration obtained in step (7).
The efficiency of the converter shall be greater than 90 percent. Adjustment of the converter temperature may be necessary to maximize the efficiency. If the converter does not meet the conversion-efficiency specifications, repair or replace the unit prior to testing. Repeat the procedures of this section with the repaired or new converter.
(c)Linearity check. For each range used, check linearity as follows:
(1) With the operating parameters adjusted to meet the converter efficiency check and the quench checks, zero the analyzer.
(2) Span the analyzer using a calibration gas that will give a response of approximately 90 percent of full-scale concentration.
(3)Recheck the zero response. If it has changed more than 0.5 percent of full scale, repeat steps (1) and (2).
(4) Record the response of calibration gases having nominal concentrations of 30, 60 and 90 percent of full-scale concentration. It is permitted to use additional concentrations.
(5) Perform a linear least-square regression on the data generated. Use an equation of the form y=mx where x is the actual chart deflection and y is the concentration.
(6) Use the equation z=y/m to find the linear chart deflection (z) for each calibration gas concentration (y).
(7) Determine the linearity (%L) for each calibration gas by:
(8) The linearity criterion is met if the %L is less than ±2 percent of each data point generated. For each emission test, a calibration curve of the form y=mx is to be used. The slope (m) is defined for each range by the spanning process.
(9) If the %L exceeds ±2 percent for any data point generated, repair or replace the analyzer or calibration bottles prior to testing. Repeat the procedures of this section with the repaired or replaced equipment or gases.
(10) Perform a converter-efficiency check (see paragraph (b) of this section).
(11) The operating parameters are defined as “optimized” at this point.