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110 Model 2700 Transmitter with PROFIBUS-PA
Troubleshooting
6.14 Checking sensor coils and RTD
Problems with sensor coils can cause several alarms, including sensor failure and a variety of
out-of-range conditions. Checking the sensor coils involves testing the terminal pairs and testing for
shorts to the case.
6.14.1 9-wire remote or remote core processor with remote transmitter installation
If you have a 9-wire remote or a remote core processor with remote transmitter installation:
1. Power down the transmitter.
2. If the transmitter is in a hazardous area, wait five minutes.
3. Remove the end-cap from the core processor housing.
4. Unplug the terminal blocks from the terminal board.
5. Using a digital multimeter (DMM), check the circuits listed in Table 6-12 by placing the
DMM leads on the unplugged terminal blocks for each terminal pair.
6. There should be no open circuits (i.e., no infinite resistance readings). The LPO and RPO
readings should be the same or very close (±5 ohms). If there are any unusual readings, repeat
the coil measurement tests at the sensor junction box to eliminate the possibility of faulty
cable. The readings for each coil pair should match at both ends.
If the cable is faulty, replace the cable.
7. Leave the core processor terminal blocks disconnected. At the sensor, remove the lid of the
junction box and test each sensor terminal for a short to case by placing one DMM lead on the
terminal and the other lead on the sensor case. With the DMM set to its highest range, there
should be infinite resistance on each lead. If there is any resistance at all, there is a short to the
case.
Table 6-12 Circuit terminal pairs
Circuit Test terminal pair
Drive coil Brown to red
Left pickoff coil (LPO) Green to white
Right pickoff coil (RPO) Blue to gray
Resistance temperature detector (RTD) Yellow to violet
Lead length compensator (LLC) (All sensors except CMF400 IS and T-Series)
Composite RTD (T-Series only)
Fixed resistor (CMF400 IS only)
Yellow to orange