Teledyne GFC-7000T - Trace CO2 Analyzer - manual - Manual (Page 214)

Theory of Operation Model GFC7000TA Carbon Dioxide Analyzer
Teledyne Analytical Instruments 196
9.2.3. Purge Gas Pressure Control
In order to ensure that all of the ambient CO
2
is purged from the GFC Wheel housing an adequate supply
of dried air, scrubbed of CO
2
must be supplied to the PURGE AIR inlet at the back of the instrument.
 The minimum gas pressure of the source of purge air should be 7.5 psig.
 If the source of the purge air is shared by a Teledyne TAI’s T700 (as shown in figure 3-7) the
minimum gas pressure should be 25 psig and should not exceed 35 psig.
In order to maintain the proper pressure differential between the inside of the GFC wheel housing and
ambient air, the GFC 7000TA design includes a manually adjustable pressure regulator (see Figure 3-5
and Figure 3-6 for
Purge Gas Pressure Regulator
) that maintains the pressure of the purge air feed at 7.5
psig.
9.2.4. Particulate Filter
The Model GFC 7000TA Analyzer comes equipped with a 47 mm diameter, Teflon, particulate filter with a
5 micron pore size. The filter is accessible through the front panel, which folds down to allow access, and
should be changed according to the suggested maintenance schedule described in Table 9-1.
9.2.5. Pneumatic Sensors
9.2.5.1. Sample Pressure Sensor
An absolute value pressure transducer plumbed to the outlet of the sample chamber is used to measure
sample pressure. The output of the sensor is used to compensate the concentration measurement for
changes in air pressure. This sensor is mounted to a printed circuit board with the sample flow sensor on
the sample chamber; see the following section and Figure 3-3.
9.2.5.2. Sample Flow Sensor
A thermal-mass flow sensor is used to measure the sample flow through the analyzer. The sensor is
calibrated at the factory with ambient air or N
2
, but can be calibrated to operate with samples consisting of
other gases such as CO
2
, See Section 9.3.4. This sensor is mounted to a printed circuit board with the
Sample Pressure sensor on the sample chamber; see the previous section and Figure 3-3.