Teledyne API Model 200AH NOX Analyzer Instruction Manual, 06492, Rev. G2 9-5 Table 9-1: Test Functions (Continued) Test Function Factory Set-Up Comment
PMT 0-5000 mV This is the instantaneous output of the PMT. During normal
operation the value varies widely as the M200AH switches from
NO to NOx modes. Changes in reading will be synchronized with
valve switching. The PMT voltage values will be relatively constant
when:
1. Electric test - variation in the 2000 mV signal observed will be
sampling errors of the V/F board and preamp noise. See
Section 9.1.3.2.
2. Optic test - variation in the 100 mV signal will be PMT dark
current, preamp, HVPS plus item 1 above. See Section 9.1.3.3.
3. Sampling zero gas - signal from 1, 2 plus signal from ozone
generator air.
4. Sampling pure NO span gas - signal will be 1, 2, 3, above plus
signal from chemiluminescent reaction. Slight pulsation’s will
be noticed as the M200AH switches from NO to NOx. This is
due to differences in flowrates (Cv) in each channel. These
differences are taken out in the calibration process resulting in
slightly different slopes for the NO and NOx channels. Large
pulsation’s when switching to the NOx channel is indicative of
a bad converter.
5. When sampling zero gas the PMT reading should be less than
50 mV and relatively constant.
High or noisy readings could be due to:
1. Electric test - variation in the 2000 mV signal observed will be
sampling errors of the V/F board and preamp noise. See
Section 9.1.3.2.
2. Excessive background light which is caused by a possible
contaminated reaction cell.
3. Humidity (undried ambient air) in the ozone generator feed air.
4. PMT recently exposed to room light. It takes 24-48 hours for
the PMT to adapt to dim light.
5. Light leak in reaction cell.
6. Miswiring of the thermoelectric cooler causing the PMT to be
heated.
(table continued)