Ametek Thermox CEM O2/TM, User Manual

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Maintenance and Troubleshooting | 6-11
Note: The cell thermocouple compensation circuit on the 80471SE,
80485SE, 80467SE and 80505SE sensor boards is different in compari-
son to the 80418SE sensor board that was supplied with Series 2000
based systems prior to 1996 (CE Marked Systems).
The 80418SE uses the 40.2-ohm resistor on the display module to
sense the current sourced from the AD592. The compensation current
produces a voltage drop across the resistor on the display module and
then adds this voltage to the raw T/C mVs sensed at the T/C + and -
connections at the wiring board and at the sensor board.
The change was implemented on later sensor board designs (80471SE,
80485SE, 80467 SE and 80505SE) due to the confusion caused by see-
ing a display that was approximately 12 mVs higher than the voltage
measured at the terminals on the wiring board.