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Teledyne API - Model T200H/T200M Operation Manual Principles of Operation
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condition (2:1 pressure ratio) through the sample gas critical flow orifice (Section 8.3.3).
If the temperature/pressure compensation (TPC) feature is turned on (Section 8.8.3), the
output of this sensor is also used to supply pressure data for that calculation.
The actual pressure value is viewable through the analyzer’s front panel display as the test
function
SAMP . The flow rate of the sample gas is displayed as SAMP FLW .
8.3.10.3. Vacuum Pressure Sensor
An absolute pressure transducer connected to the exhaust manifold is used to measure the
pressure downstream from and inside the instrument’s reaction cell. The output of the
sensor is used by the CPU to calculate the pressure differential between the gas upstream
of the reaction cell and the gas downstream from it and is also used as the main diagnostic
for proper pump operation. If the ratio between the upstream pressure and the
downstream pressure falls below 2:1, a warning message (
SAMPLE FLOW WARN ) is
displayed on the analyzer’s front panel (Section 6.2.2) and the sample flow rate will
display
XXXX instead of an actual value. If this pressure exceeds 10 in-Hg-A, an RCEL
PRESSURE WARNING Is issued, even though the analyzer will continue to calculate a
sample flow up to ~14 in Hg.
Also, if the temperature/pressure compensation (TPC) feature is turned on (Section 8.8.3),
the output of this sensor is used to supply pressure data for that calculation. This meas-
urement is viewable through the analyzer’s front panel as the test function
RCEL .
8.3.10.4. O
3
Supply Air Flow Sensor
A mass flow meter connected between the ozone dryer and the O
3
generator measures the
flow rate of O
3
supply air through the analyzer. This information is used to validate the
O
3
gas flow rate. If the flow rate exceeds ±15% of the nominal flow rate (250 cm³/min), a
warning message OZONE FLOW WARNING is displayed on the analyzer’s front panel
(Section 6.2.2) and the O
3
generator is turned off. As second warning, OZONE GEN
OFF , is displayed. This flow measurement is viewable through instrument’s front panel
display as the test function OZONE FL .
8.3.11. DILUTION MANIFOLD
Certain applications require to measure NO
X
in sample gases that do not contain any
oxygen. However, the molybdenum NO
2
converter requires a minimum amount of
oxygen to operate properly and to ensure constant conversion efficiency. For these
special applications, the analyzer may be equipped with a dilution manifold (Figure 8-13)
to provide the instrument with an internal sample stream that contains about 2.5% O
2
.
This manifold is mounted between converter housing and vacuum manifold on a small
mounting bracket. If the dilution manifold is to be mounted in the T200H/M analyzer.
The manifold is equipped with two orifice holders that control the flow of the O
2
-free
sample gas and the bleeds in a small amount of zero air before the combined sample
stream goes to the NO/NO
X
valve for measurement. The zero air is produced by an
external zero air scrubber cartridge, mounted on the rear panel.
The dilution manifold is not temperature controlled, although the residual heat of the NO
2
converter housing provides some temperature stability. Tight temperature stability is not
critical to the dilution application.
07270D DCN7141