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TROUBLESHOOTING & REPAIR PROCEDURES Model 360E Instruction Manual
11.2.2.6. 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.
11.2.3. 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.
11.3. Calibration Problems
11.3.1. Miscalibrated
There are several symptoms that can be caused by the analyzer being miss-calibrated. This condition is
indicated by out of range Slopes and Offsets as displayed through the test functions and is frequently caused by
the following:
1. BAD SPAN GAS. This can cause a large error in the slope and a small error in the offset. Delivered
from the factory, the M360E’s slope is within ±15% of nominal. Bad span gas will cause the analyzer to
be calibrated to the wrong value. If in doubt have the span gas checked by and independent lab.
2. CONTAMINATED ZERO GAS. Excess H
2
O can cause a positive or negative offset and will indirectly
affect the slope.
3. Dilution calibrator not set up correctly or is malfunctioning. This will also cause the slope, but not the
zero, to be incorrect. Again the analyzer is being calibrated to the wrong value.
4. Too many analyzers on the manifold. This can cause either a slope or offset error because ambient gas
with its pollutants will dilute the zero or span gas.
204 05232 Rev B3