Ametek Thermox CEM O2/TM, User Manual

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6-10 | Thermox CEM O2/TM Analyzer
Reversed thermocouple wires
To check if the thermocouple wires are reversed, use the controller to
display the thermocouple millivolts so that they appear on the front
panel display. If the millivolts are negative, the thermocouple wires are
reversed.
Thermocouple compensation circuit check

Using a volt meter, measure across terminals 2 (-) and 12 (+) on the
sensor board. If approximately 15 volts is not present, check that inter-
connecting wiring is correct.

If interconnecting wiring is correct, check across 15V Sup and 15V
Com on the control unit for approximately 15 volts.
-
If 15 volts is not present, check fuse F1 on the wiring card.
If this fuse is OK, replace the control unit power supply/keypad
module.
-
If this fuse is not OK, replace the fuse (1/4 amp, 125 volts, IEC
speed type FF).

Check the interconnecting wiring for shot circuits before applying
power to the control unit.
-
If you do not measure 15 volts at terminals 2 (-) and 12 (+) of the
sensor board, measure across terminals D (+) and 6 (-) on the sen-
sor board. The circuit compensates to absolute zero (0°K) so 273°C
is 11 mV and 25°C board temperature is 1 mV that results in the 12
mVs added from the compensation circuit.
-
Twelve millivolts should be measured (this signal is a function of
ambient temperature and may vary up to ± 2 millivolts at extreme
ambient temperature).
-
If you don’t measure this voltage, replace the sensor board.
For a furnace temperature set point for a 615°C oxygen cell temperature,
the furnace thermocouple output would be about 27 mVs (take memory
location 88 which is the T/C Ratio calculated during the primary - thermal
calibration and divide the cell temperature by this value to come up with
the furnace temperature set point).