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Teledyne API - Model 200EH/EM Operation Manual Theory of Operation
207
10.3.10.3. 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 (Section6.2.2) 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 10.7.3), the output of this
sensor is used to supply pressure data for that cal
culation. This measurement is viewable through the
analyzer’s front panel as the test function
RCEL.
10.3.10.4. O
3
Supply Air Flow Sensor
A mass flow meter connected between the Perma Pure
®
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 (80 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.
10.3.11. 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 M200E analyzer may be equipped with a dilution
manifold (Figure 10-10-15) to provide the instrument with an intern
al 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 M200EH/EM analyzer, it will fit on the back of the shown bracket as
the front of the bracket is occupied by the bypass manifold.
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 (Figure 3-2 and
)LJXUH).
The dilution manifold is n
ot 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.
04521C (DCN5731)