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Model 9110T NOx Analyzer Principles of Operation
Teledyne Analytical Instruments 337
Since this is a calculated value and not a measured reading there is no corresponding SIGNALI/O
function.
13.2.4.4. O
3
Supply Air Flow Sensor
In contrast to the sample gas flow, the ozone flow is measured with a mass flow sensor, which is
mounted on the flow/pressure sensor PCA just behind the PMT sensor assembly. Pneumatically, it lies
between the Perma Pure
®
dryer and the O
3
. This mass flow sensor has a full scale range of 0-1000
cm³/min and can be calibrated through software to its span point (Section 9.7).
Since the flow value displayed on the front panel is an actual measurement (and not a calculated value),
short term variability in the measurement may be higher than that of the sample flow, which is based on
a calculation from (more stable) differential pressures. On the other hand, any sustained drift, i.e. long-
term change, in the ozone flow rate may usually indicate a flow problem.
This information is used to validate the O
3
gas flow rate.
If the flow rate exceeds ±15% of the nominal flow rate (80 cm³/min), a warning message OZONE
FLOW WARNING is displayed on the analyzer’s front panel (see Section 4.1.2) and the O
3
generator is turned off.
A second warning, OZONE GEN OFF is also displayed.
This flow measurement is viewable through instrument’s front panel display as the test function
OZONE FL and the SIGNAL I/O function OZONE_FLOW.
As with all other test parameters, we recommend to monitor the ozone flow over time for predictive
diagnostics and maintenance evaluation.