Teledyne 200E, Instruction Manual, Page: 185 / 302

Theory of Operation Model 200E Instruction Manual
10.2.10. Pneumatic Sensors
NOTE
The M200E displays all pressures in inches of mercury absolute (in-Hg-A), i.e.
absolute pressure referenced against zero (a perfect vacuum).
The M200E 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.
10.2.10.1. 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 and the pressure that 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 10.2.9). If the temperature/pressure compensation (TPC) feature is turned on
(Section 10.4.3), the output of this sensor is also used to supply pressure data for that
calculation.
The actual pressure measurement is viewable through the analyzer’s front panel display as
the test function SAMP . The flow rate of the sample gas is viewable as the SAMP FLW test
function.
10.2.10.2. 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 rate up to about
14 in-Hg-A.
Also, if the temperature/pressure compensation (TPC) feature is turned on (Section 10.4.3),
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 .
10.2.10.3. 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
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