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Troubleshooting & Repair Model GFC7001E Carbon Dioxide Analyzer
Teledyne Analytical Instruments 285
13.4. OTHER PERFORMANCE PROBLEMS
Dynamic problems (i.e. problems which only manifest themselves when the analyzer is monitoring sample gas)
can be the most difficult and time consuming to isolate and resolve. The following provides an itemized list of the
most common dynamic problems with recommended troubleshooting checks and corrective actions.
13.4.1. TEMPERATURE PROBLEMS
Individual control loops are used to maintain the set point of the absorption bench, filter wheel and IR photo-
detector temperatures. If any of these temperatures are out of range or are poorly controlled, the GFC
7001E/EM will perform poorly.
13.4.1.1. Box or Sample Temperature
BOX TEMPERATURE
The box temperature sensor is mounted to the motherboard and cannot be disconnected to check its resistance.
Rather check the BOX TEMP signal using the SIGNAL I/O function under the DIAG Menu (See Section 7.3).
This parameter will vary with ambient temperature, but at ~30
o
C (6-7° above room temperature) the signal
should be ~1450 mV.
SAMPLE TEMPERATURE
The Sample Temperature should closely track the bench temperature. If it does not, locate the sensor, which is
located at the midpoint of the optical bench in a brass fitting. Unplug the connector labeled “Sample”, and
measure the resistance of the thermistor; at room temperature (25°C) it should be ~30K Ohms, at operating
temperature, 48°C, it should be ~ 12K Ohms
13.4.1.2. Bench Temperature
There are three possible failures that could cause the Bench temperature to be incorrect.
1. The heater mounted to the bottom of the Absorption bench is electrically shorted or open.
Check the resistance of the two heater elements by measuring between pin 2 and 4 (~76 Ohms), and
pin 3 and 4 (~330 Ohms), of the white five-pin connector just below the sample temperature sensor
on the Bench (pin 1 is the pointed end).
2. Assuming that the I
2
C bus is working and that there is no other failure with the relay board, the solid-
state relay (K2) on the relay board may have failed.
Using the BENCH_HEATER parameter under the signal I/O function, as described above, turn on
and off K2 (D3 on the relay board should illuminate as the heater is turned on).
Check the AC voltage present between pin 2 and 4, for a 100 or 115 VAC model, and pins 3 and 4,
for a 220-240 VAC model.
CAUTION
ELECTRICAL SHOCK HAZARD
Hazardous Voltages are present during this test
3. If the relay has failed there should be no change in the voltage across pins 2 and 4 or 3 and 4. Note:
K2 is in a socket for easy replacement.
4. If K2 checks out OK, the thermistor temperature sensor located on the optical bench near the front of
the instrument could be at fault.
Unplug the connector labeled “Bench”, and measure the resistance of the thermistor.