Teledyne T200, Руководство по эксплуатации, Страница: 303 / 425

Teledyne API
– T200 NO/NO
2
/NO
X
Analyzer Operation Manual Principles of Operation
301
13.2.4.3. SAMPLE GAS FLOW CALCULATION
Sample gas flow in the T200 analyzer is not a directly measured value, but is rather
calculated based on the measured pressure differential across the sample gas critical
flow orifice. Specifically, the upstream reading of the sample pressure sensor is
compared to the downstream pressure reading of the vacuum pressure sensor and this
differential is used, by the analyzer‟s CPU, to derive the gas flow rate through the
reaction cell.

The results of this calculation are viewable from the instruments front panel via the
test function
SAMP FLW.

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 Sample 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.
06858E DCN7057