92.121—Oxides of nitrogen analyzer calibration and check.
(a)
Quench checks; NO
X
analyzer. (1) Perform the reaction chamber quench check for each model of high vacuum reaction chamber analyzer prior to initial use.
(2)
Perform the reaction chamber quench check for each new analyzer that has an ambient pressure or “soft vacuum” reaction chamber prior to initial use. Additionally, perform this check prior to reusing an analyzer of this type any time any repairs could potentially alter any flow rate into the reaction chamber. This includes, but is not limited to, sample capillary, ozone capillary, and if used, dilution capillary.
(ii)
Introduce a mixture of CO2 calibration gas and NOX calibration gas to the CL analyzer. Dynamic blending may be used to provide this mixture. Dynamic blending may be accomplished by analyzing the CO2 in the mixture. The change in the CO2 value due to blending may then be used to determine the true concentration of the NOX in the mixture. The CO2 concentration of the mixture shall be approximately equal to the highest concentration experienced during testing. Record the response.
(iii)
Recheck the calibration. If it has changed more than ±1 percent of full scale, recalibrate and repeat the quench check.
(iv)
Prior to testing, the difference between the calculated NOX response and the response of NOX in the presence of CO2 (step in paragraph (a)(3)(ii) of this section must not be greater than 3.0 percent of full-scale. The calculated NOX response is based on the calibration performed in step in paragraph (a)(3)(i) this section.
(b) Oxides of nitrogen analyzer calibration.
(1)
Every 30 days, perform a converter-efficiency check (see paragraph (b)(2) of this section) and a linearity check (see paragraph (b)(3) of this section).
(2)
Converter-efficiency check. The apparatus described and illustrated in Figure B121-1 of this section 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:
(iii)
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.
(iv)
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. The NO2 content of the gas mixture shall be less than 5 percent of the NOX concentration.
(v)
With the oxides of nitrogen analyzer in the NO Mode, record the concentration of NO indicated by the analyzer.
(vi)
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 in paragraph (b)(2)(v) of this section. Record the concentration of NO in this NO O2 mixture.
(vii)
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 in paragraph (b)(2)(v) of this section. There must be at least 10 percent unreacted NO at this point. Record the concentration of residual NO.
(viii)
Switch the oxides of nitrogen analyzer to the NOX mode and measure total NOX. Record this value.
(ix)
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.
(x)
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 in paragraph (b)(2)(iv) of this section.
(xi)
Calculate the efficiency of the NOX converter by substituting the concentrations obtained into the following equation:
where:
a=concentration obtained in paragraph (b)(2)(viii) of this section.
b=concentration obtained in paragraph (b)(2)(ix) of this section.
c=concentration obtained in paragraph (b)(2)(vi) of this section.
d=concentration obtained in paragraph (b)(2)(vii) of this section.
(B)
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.
(i)
With the operating parameters adjusted to meet the converter efficiency check and the quench checks, zero the analyzer.
(ii)
Span the analyzer using a calibration gas that will give a response of approximately 90 percent of full-scale concentration.
(iii)
Recheck the zero response. If it has changed more than 0.5 percent of full scale, repeat steps in paragraphs (b)(3)(i) and (b)(3)(ii) of this section.
(iv)
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.
(v)
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.
(vi)
Use the equation z=y/m to find the linear chart deflection (z) for each calibration gas concentration (y).
Percent L=(100)(z−x)/(Full-scale chart deflection)
(viii)
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.
(ix)
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.
(4)
Converter checking gas. If the converter quick-check procedure is to be employed, paragraph (b)(5) of this section, a converter checking gas bottle must be named. The following naming procedure must occur after each converter efficiency check, paragraph (b)(2) of this section.
(i)
A gas bottle with an NO2 concentration equal to approximately 80 percent of the most common operation range shall be designated as the converter checking gas bottle. Its NO concentration shall be less than 25 percent of its NO2 concentration, on a volume basis.
(ii)
On the most common operating range, zero and span the analyzer in the NOX mode. Use a calibration gas with a concentration equal to approximately 80 percent of the range for spanning.
(iii)
Introduce the converter checking gas. Analyze and record concentrations in both the NOX mode (X) and NO mode (Y).
(iv)
Calculate the concentration of the converter checking gas using the results from step in paragraph (b)(4)(iii) of this section and the converter efficiency from paragraph (b)(2) of this section as follows:
Concentration=(((X−Y)(100))/Efficiency) Y
(iii)
Compare the observed concentration with the concentration assigned under the procedure in paragraph (b)(4) of this section. If the observed concentration is equal to or greater than 90 percent of the assigned concentration, the converter operation is satisfactory.
(c) 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 normally used operating range with NO-in-N2 calibration gases with nominal concentrations of 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 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, the best-fit non-linear equation which represents the data to within 2 percent of each test point shall be used to determine concentration.
(d)
If a stainless steel NO2 to NO converter is used, condition all new or replacement converters. The conditioning consists of either purging the converter with air for a minimum of 4 hours or until the converter efficiency is greater than 90 percent. The converter must be at operational temperature while purging. Do not use this procedure prior to checking converter efficiency on in-use converters.
Code of Federal Regulations
Code of Federal Regulations
462