Teledyne GFC-7000T - Trace CO2 Analyzer - manual - Manual (Page 211)

Theory of Operation Model GFC7000TA Carbon Dioxide Analyzer
Teledyne Analytical Instruments 193
9.2. Pneumatic Operation
CAUTION
It is important that the sample airflow system is both leak tight and not pressurized
over ambient pressure.
Regular leak checks should be performed on the analyzer as described in the
maintenance schedule, Table 9-1.
Procedures for correctly performing leak checks can be found in Section 9.3.3.
An internal pump evacuates the sample chamber creating a small vacuum that draws sample gas into the
analyzer. Normally the analyzer is operated with its inlet near ambient pressure either because the
sample is directly drawn at the inlet or a small vent is installed at the inlet. There are several advantages
to this “pull through” configuration.
 By placing the pump down stream from the sample chamber several problems are avoided.
 First the pumping process heats and compresses the sample air complicating the measurement
process.
 Additionally, certain physical parts of the pump itself are made of materials that might chemically
react with the sample gas.
 Finally, in certain applications where the concentration of the target gas might be high enough to be
hazardous, maintaining a negative gas pressure relative to ambient means that should a minor leak
occur, no sample gas will be pumped into the atmosphere surrounding analyzer.