Ametek Thermox CEM O2/TM, User Manual

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Maintenance and Troubleshooting | 6-9
Thermocouple Checks
Open thermocouple
Disconnect power to the control unit and the sensor. Measure across ter-
minals “C” and “D” on the sensor board with an ohm meter. If an open is
measured, replace the thermocouple.
Shorted/failed thermocouple
Check that the thermocouple leads are not shorted to chassis ground. To
do this, use an ohm meter to measure between terminal C on the sensor
board and chassis ground, and between terminal D on the sensor board
and chassis ground. If shorted, replace the thermocouple.
To check the thermocouple you will need a digital volt meter and a Type K
test meter.

First display the thermocouple millivolts on the front panel display.
The display should measure a positive voltage.

If the display measures a negative voltage, reverse the wires leading to
pins C and D on the sensor board.

To check the continuity of the thermocouple, measure resistance
across pins C and D on the sensor board. The resistance should be less
than 5 ohms.

If this doesn’t solve the problem, remove the thermocouple from the
sensor and connect a Type K test meter.
-
Using a thermometer, check the temperature of an environment.
Place the thermocouple in this same environment and check that
the reading of the test meter measures the same temperature as
the thermometer. If the thermocouple measures the temperature
incorrectly (greater than 1% of expected temperature), replace the
thermocouple.