Configuration and Use Manual 235
Diagnostics and Troubleshooting
Diagnostics and Troubleshooting Specifications – Model 3350/3700Specifications – Model 3300/3500Measurement Performance
Figure 22-6 Core processor resistance test
22.20 Checking sensor coils and RTD
Problems with sensor coils can cause several alarms, including sensor failure and a variety of
out-of-range conditions. Testing the sensor coils involves testing the terminal pairs and testing for
shorts to case.
22.20.1 Remote core processor with remote transmitter installation
If you have 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. At the core processor:
a. Remove the end-cap.
b. Unplug the terminal blocks from the terminal board.
c. Using a digital multimeter (DMM), check the pickoff coils listed in Table 22-16 by
placing the DMM leads on the unplugged terminal blocks for each terminal pair. Record
the values.
4. 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 Ω). If there are any unusual readings, repeat the
coil resistance tests at the sensor junction box to eliminate the possibility of faulty cable. The
readings for each coil pair should match at both ends.
Table 22-16 Coils and test terminal pairs
Coil 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 I.S. and T-Series)
Composite RTD (T-Series sensors only)
Fixed resistor (CMF400 I.S. sensors only)
Yellow to orange
40 kΩ – 50 kΩ
20 kΩ – 25 kΩ
20 kΩ – 25 kΩ
