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Configuration and Use Manual 117
Troubleshooting
Operation AppendicesMaintenance and TroubleshootingCommissioning
10.23.3 Low pickoff voltage
Low pickoff voltage can be caused by several problems. See Table 10-6.
10.24 Checking sensor circuitry
Problems with sensor circuitry can cause several alarms, including sensor failure and a variety of
out-of-range conditions. Testing involves:
• Inspecting the cable that connects the transmitter to the sensor
• Measuring the resistances of the sensor's pin pairs and RTDs
• Ensuring that the circuits are not shorted to each other or to the sensor case
Table 10-5 Drive gain problems, causes, and remedies
Cause Possible remedy
Excessive slug flow • See Section 10.17.
Entrained air • Correct the process.
Cavitation or flashing • Increase inlet or back pressure at the sensor.
• If a pump is located upstream from the sensor, increase the distance
between the pump and sensor.
Plugged flow tube • Purge the flow tubes.
Mechanical binding of sensor tubes • Ensure sensor tubes are free to vibrate. Possible problems include:
- Pipe stress. Check for pipe stress and eliminate if present.
- Lateral tube shift due to hammer effect. If this is a possibility,
contact Micro Motion.
- Warped tubes caused by overpressurization. If this is a possibility,
contact Micro Motion.
Incorrect sensor type configured • Verify sensor type configuration, then verify sensor characterization.
See Section 4.2.
Open drive or left pickoff sensor coil • Contact Micro Motion.
Drive board or module failure, cracked flow tube,
or sensor imbalance
• Contact Micro Motion.
Table 10-6 Low pickoff voltage causes and remedies
Cause Possible remedy
Slug flow • See Section 10.17.
No tube vibration in sensor • Check for plugging.
Moisture in the sensor electronics • Eliminate the moisture in the sensor electronics.
Damaged sensor • Ensure sensor is free to vibrate (no mechanical binding).
Possible problems include:
- Pipe stress. Check for pipe stress and eliminate if
present.
- Lateral tube shift due to hammer effect. If this is a
possibility, contact Micro Motion.
- Warped tubes caused by overpressurization. If this is a
possibility, contact Micro Motion.
• Test sensor circuitry. See Section 10.24.
• Contact Micro Motion.