To know whether your pickoff voltage is unusually low, you must collect pickoff voltage
data during the problem condition and compare it to pickoff voltage data from a period of
normal operation.
Drive gain and pickoff voltage are inversely proportional. As drive gain increases, pickoff
voltages decrease and vice versa.
Possible causes and recommended actions for low pickoff voltageTable 10-6:
Possible cause Recommended actions
Cavitation or flashing; settling of
two-phase or three-phase fluids
• Increase the inlet or back pressure at the sensor. Increasing
back pressure is recommended. Applying back pressure
downstream from the sensor can prevent flashing inside the
sensor tubes. That way, if the process fluid is going to flash,
it will do so downstream from the sensor after it has been
measured.
• If a pump is located upstream from the sensor, increase the
distance between the pump and sensor.
• The sensor may need to be reoriented or repositioned. Con-
sult the installation manual for your sensor.
Faulty wiring runs between the
sensor and transmitter
Verify wiring between sensor and transmitter.
Process flow rate beyond the
limits of the sensor
Verify that the process flow rate is not out of range of the sen-
sor.
Two-phase flow Check for two-phase flow. See Section 10.24.
The vibrating element is not vi-
brating
• Check for plugging or deposition.
• Ensure that the vibrating element is free to vibrate (no me-
chanical binding).
• Verify wiring.
Moisture in the sensor electron-
ics
Eliminate the moisture in the sensor electronics.
The sensor is damaged, or sen-
sor magnets may have become
demagnetized
Replace the sensor.
10.26.1 Collect pickoff voltage data
Pickoff voltage data can be used to diagnose a variety of process and equipment
conditions. Collect pickoff voltage data from a period of normal operation, and use this
data as a baseline for troubleshooting.
Procedure
1. Navigate to the pickoff voltage data.
2. Observe and record data for both the left pickoff and the right pickoff, over an
appropriate period of time, under a variety of process conditions.
Troubleshooting
148 Micro Motion Model 1500 Transmitters with Analog Outputs
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