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Theory of Operation Teledyne API - Model 200EH/EM Operation Manual
206
10.3.10. PNEUMATIC SENSORS
NOTE
The M200EH/EM displays all pressures in inches of mercury absolute (in-Hg-A), i.e.
absolute pressure referenced against zero (a perfect vacuum).
The M200EH/EM uses three pneumatic sensors to verify gas streams. These sensors are located on a printed
circuit assembly, called the pneumatic pressure/flow sensor board, located just behind the sensor assembly.
10.3.10.1. Vacuum Manifold
The vacuum manifold is the central exit port for all analyzer pneumatics. All gas streams of the analyzer exit
through this assembly and connect to the instrument’s pump. Figure 10-10-14 shows the standard
configuration. Configurations will vary depending on the option
al equipment that is installed. An IZS option, for
example, will add another FT8 connector and orifice assembly to the manifold, an optional sample dryer may
add a Tee-fitting so that two ¼” tubes can be connected to the same port.
At this time, the vacuum manifold does not yet support the orifice holder shown in Figure 9-6. To exchange the
critical orifi
ce installed in the vacuum manifold, the user nee
ds to either blow the orifice out with reversed
pressure or remove the entire manifold for this task. However, orifices installed in the vacuum manifold should
not have to be cleaned under normal circumstances.
Figure 10-10-14: Vacuum Manifold
10.3.10.2. Sample Pressure Sensor
An absolute pressure transducer connected to the input of the NO/NO
X
valve is used to measure the pressure of
the sample gas before it enters the analyzer’s reaction cell. This is the “upstream” pressure mentioned above,
which is used to compute sample flow rate. In conjunction with the vacuum pressure sensor, it is also used to
validate the critical flow condition (2:1 pressure ratio) through the sample gas critical flow orifice (Section 10.3.3).
If
the temperature/pressure compen
sation (TPC) feature is turned on (Section 10.7.3), the output of this sensor
is also used to supply pressure data for that calculation.
The act
ual 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.
04521C (DCN5731)