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Model 9110T NOx Analyzer Troubleshooting & Service
Teledyne Analytical Instruments 292
A performance failure of the converter itself.
12.7.10.1. NO
2
NO Converter Electrical System
NO
2
converter heater failures can be divided into two possible problems:
Temperature is reported properly but heater does not heat to full temperature.
In this case, the heater is either disconnected or broken or the power relay is broken.
Disconnect the heater cable coming from the relay board and measure
the resistance between any two of the three heater leads with a multi-
meter.
The resistance between A and B should be about 1000 Ω.
That between A and C should be the same as between B and C, about
500 Ω each.
If any of these resistances is near zero or without continuity, the heater is
broken.
Temperature reports zero or overload (near 500° C).
This indicates a disconnected or failing thermocouple or a failure of the thermocouple circuit.
Check that the thermocouple is connected properly and the wire does not
show signs of a broken or kinked pathway.
If it appears to be properly connected, disconnect the yellow
thermocouple plug (marked K) from the relay board and measure the
voltage (not resistance) between the two leads with a multi-meter
capable of measuring in the low mV range.
The voltage should be about 12 mV (ignore the sign) at 315° C and about
0 mV at room temperature.
Measure the continuity with an Ohm-meter.
It should read close to zero Ω. If the thermo-couple does not have continuity, it is broken.
If it reads zero voltage at elevated temperatures, it is broken.
To test the thermocouple at room temperature, heat up the converter can (e.g., with a heat gun) and
see if the voltage across the thermocouple leads changes.
If the thermocouple is working properly, the electronic circuit is broken.
ATTENTION
COULD DAMAGE INSTRUMENT AND VOID WARRANTY
If the thermocouple is broken, do NOT replace the thermocouple without first
consulting the factory; using the wrong Type could cause permanent damage to
the instrument. The Type K thermocouple has a red and a yellow wire. If in
doubt, consult the factory.