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Teledyne API Model 200A NO
X
Analyzer Instruction Manual, 02246, Rev. G, DCN 5247
Stability
The instrument noise is computed using the standard deviation of the last 10 minutes of data,
with the value being computed at the end of each NO/ NO
x
cycle. It is computed for the NO
x
channel only. The value only becomes meaningful if sampling a constant concentration for more
than 20 minutes, so the various software filters can stabilize. The value shown should be
compared to the value observed in Table 2-2-6.
Sample Flow
The SAMPLE FLOW test function is com
puted from the pressure measured up-stream of the
sample flow orifice. The pressure down-stream of the orifice is also checked to assure the
assumptions of the equation are valid. SAMPLE FLOW will indicate variations in flow caused
by changes in atmospheric pressure, but will not detect a plugged sample flow orifice. The
nominal value is 500 ± 50 cc/min.
Ozone Flow
The OZONE FLOW test function is directly measured by a solid state flow meter. Variations in
this value indicate variations in ozone flow. The nominal value for ozone flow is 60 - 90 cc/min.
PMT Voltage
The PMT VOLTAGE shows the PMT signal at the output of the preamp board. The waveform
of the PMT voltage can be complex, and vary from near 0 mV when zero gas is in the reaction
cell to 5000 mV when a high concentration of NO
x
is being measured. If the PMT reading is
consistently 5000 mV, that indicates an off-scale reading. Typical readings bounce around,
which is normal.
Normalized PMT Voltage
Like the PMT Voltage TEST function above, the NORMALIZED PMT VOLTAGE measures
the PMT signal at the output of the preamp board. The difference here is that several
normalization functions are applied to this signal before it is displayed. The most important is the
temperature and pressure compensation factors. If NORM PMT is used as suggested in the
Factory Calibration Procedure (Section 9.1.6) the M200A will be correctly calibrated.
AZERO Voltage
This test measurement is the AUTOZERO voltage. It indicates the most recent reading from the
AutoZero circuit. The units are mV and from – 20 to 150 are acceptable.
5-9
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