Teledyne API Model 200AH NOX Analyzer Instruction Manual, 06492, Rev. G2
5-12
Signal Stability (STABIL, NOX STB)
The instrument noise is computed by calculating the standard deviation of the last 10 minutes of
concentration data. If NO/ NOX switching mode is selected, the noise reading is that of the NOX
channel. If NO only or NOX only mode is selected the Noise applies to the mode selected. The
noise value only becomes meaningful if sampling a constant concentration for more than
10 minutes. The noise value should be compared to the value observed in the factory check-out.
Sample Flow (SAMP FLW)
The SAMPLE FLOW test function is computed 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. This will register variations in flow caused by changes in
atmospheric pressure, but will not detect a plugged sample flow orifice. The sample flow into the
reaction cell is 50 10 cc/min with a bypass flow of 250 cc/min 50. The instrument reports a
flow of 290 50 cc/min.
Ozone Flow (OZONE FLW)
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 250
10 cc/min.
PMT Voltage (PMT)
The PMT VOLTAGE measures 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 there is large amounts of NO being measured. If the PMT reading
is consistently 5000 mV, that indicates an off-scale reading. Typical readings bounce around,
which is normal.
AutoZero Voltage (AZERO)
The AutoZero Voltage is the PMT output when the AutoZero valve is actuated. It provides a
zero reference which is subtracted from all NO and NOX readings. The value typically will be
near
0 mV. Readings in the range –10 to +50 mV are acceptable. High readings indicate a light leak
in the reaction cell, recent exposure of the PMT to light, or contamination in the reaction cell.
High Voltage Power Supply Voltage (HVPS)
The HVPS reading is a measure of the scaled-up HVPS programming voltage. The voltage used
to set the HVPS output is generated on the Preamp board. Its value is between 0 and 1 volt,
corresponding to a voltage of 0 to 1000 volts out of the HVPS. The HVPS front panel TEST
measurement should typically be in the range of 400-600V.