Teledyne GFC-7000T - Trace CO2 Analyzer - manual - Manual (Page 256)

Troubleshooting Model GFC7000TA Carbon Dioxide Analyzer
Teledyne Analytical Instruments 238
10.4. 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.
10.4.1. 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 7000TA will perform poorly.
10.4.1.1. 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 10.1.3). 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
10.4.1.2. 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.
WARNING:
HAZARDOUS VOLTAGES ARE PRESENT DURING THIS TEST