Teledyne T200, Руководство по эксплуатации, Страница: 302 / 425

Principles of Operation Teledyne API
– T200 NO/NO2/NOx Analyzer Operation Manual
300
13.2.4. PNEUMATIC SENSORS
Note The T200 displays all pressures in inches of mercury absolute (in-Hg-A), i.e.
absolute pressure referenced against zero (a perfect vacuum).
The T200 uses three pneumatic sensors to verify the flow and pressure levels of its gas
streams. They are located on a printed circuit assembly, called the pneumatic
pressure/flow sensor board, located just behind the sensor assembly. The measurements
made by these sensors are used for a variety of important calculations and diagnostics.
13.2.4.1. 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.

In conjunction with the measurement made by the vacuum pressure sensor, this
“upstream” measurement is used to compute the sample gas sample flow rate and
to validate the critical flow condition (2:1 pressure ratio) through the sample gas
critical flow orifice (Section 13.2.2).

If the Temperature/Pressure Compensation (TPC) feature is turned on (Section
13.9.2), 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
and the
SIGNAL I/O
function
SAMPLE_PRESSURE
.
13.2.4.2. 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 (see Section 4.1.2) and the sample flow rate will display
XXXX
instead of an actual value.

If this pressure exceeds 10 in-Hg-A, an
RCEL PRESS WARN
is issued, even
though the analyzer will continue to calculate a sample flow up to ~14 in Hg.

If the Temperature/Pressure Compensation (TPC) feature is turned on (see Section
13.9.2), the output of this sensor is also used to supply pressure data for that
calculation.

This measurement is viewable through the analyzer’s front panel as the test
function
RCEL
and the
SIGNAL I/O
function
RCELL_PRESSURE
.
06858E DCN7057