Teledyne GFC-7000T - Trace CO2 Analyzer - manual - Manual (Page 252)

Troubleshooting Model GFC7000TA Carbon Dioxide Analyzer
Teledyne Analytical Instruments 234
If the sample pressure is reading normal but the sample flow is reading low then it is likely that the pump
diaphragm is worn or there is an obstruction downstream of the flow sensor.
10.2.2.5. Actual Flow Does Not Match Displayed Flow
If the actual flow measured does not match the displayed flow, but is within the limits of 720-880 cc/min,
adjust the calibration of the flow measurement as described in Section 6.9.8.
10.2.2.6. Sample Pump
The sample pump should start immediately after the front panel power switch is turned ON. With the
Sample Inlet plugged, the test function PRES should read about 10”-Hg for a pump in good condition.
Readings above 10” Hg indicate that the pump needs rebuilding. If the test function SAMP FL is greater
than 10 cm
3 /min there is a leak in the pneumatic lines.
10.2.3. Poor or Stopped Flow of Purge Gas
If sufficient purge gas is not supplied to the GFC wheel housing, cyclical fluctuations in readings at zero
or low CO
2
concentrations, such as < 100 ppm, may occur. These fluctuations are the result of changes
in the CO
2
concentration of the ambient atmosphere throughout the course of the day and night. In
isolated areas with relatively few people working nearby the ambient CO
2
concentration will fall during the
day and rise during the night as rate of photosynthesis of the plants in the surrounding area decreases
and increases. In a lab environment with a relatively high human occupancy the ambient CO
2
concentration will increase during those parts of the day when the highest number of workers are present.
If the GFC wheel housing is allowed to fill with ambient air, these natural, diurnal fluctuations might be
detected by the instrument and cause it’s in its calculation of the CO
2
concentration of the sample gas to
drift.
Another possible symptom of poor or stopped purge gas flow would be the inability to measure zero
concentrations accurately at the end of a work day on a system that was calibrated at the beginning of a
workday. Although this could also be due to local fluctuations in ambient CO
2
concentration during the
day.