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Maintenance and Troubleshooting
15.16 Checking the test points
Some status alarms that indicate a sensor failure or overrange condition can be caused by problems
other than a failed sensor. You can diagnose sensor failure or overrange status alarms by checking the
meter test points. The test points include left and right pickoff voltages, drive gain, and tube
frequency. These values describe the current operation of the sensor.
To read the current test point values, use the procedure described in Section 15.11.
15.16.1
Evaluating the test points
Use the following guidelines to evaluate the test points:
•
If the drive gain is erratic, negative, or saturated, refer to Section 15.16.2.
•
If the value for the left or right pickoff does not equal the appropriate value from Table 15-4,
based on the sensor flow tube frequency, refer to Section 15.16.3.
•
If the values for the left and right pickoffs equal the appropriate values from Table 15-4, based
on the sensor flow tube frequency, record your troubleshooting data and contact the Micro
Motion customer service department for assistance. See Section 1.8.
Table 15-4
Sensor pickoff values
(1)
Sensor
ELITE Model CMF sensors
Model F025, F050, F100 sensors
Model F200 sensors
Model H025, H050, H100 sensors
Model H200 sensors
Model R025, R050, or R100 sensors
Model R200 sensors
CMF400 I.S. sensors
(1) If your sensor is not listed, contact Micro Motion. See Section 1.8.
15.16.2
Drive gain problems
Problems with drive gain can appear in several different forms:
•
Erratic drive gain (e.g., rapid shifting from positive to negative)
•
Negative drive gain
•
Saturated or excessive (near 100%) drive gain
See Table 15-5 for a list of possible problems and remedies.
Table 15-5
Drive gain problems, causes, and remedies
Cause
Excessive slug flow
Plugged flow tube
Cavitation or flashing
Configuration and Use Manual
Pickoff value
3.4 mV peak-to-peak per Hz based on sensor flow tube frequency
3.4 mV peak-to-peak per Hz based on sensor flow tube frequency
2.0 mV peak-to-peak per Hz based on sensor flow tube frequency
3.4 mV peak-to-peak per Hz based on sensor flow tube frequency
2.0 mV peak-to-peak per Hz based on sensor flow tube frequency
3.4 mV peak-to-peak per Hz based on sensor flow tube frequency
2.0 mV peak-to-peak per Hz based on sensor flow tube frequency
2.7 mV peak-to-peak per Hz based on sensor flow tube frequency
Possible remedy
See Section 15.12.
Purge the flow tubes.
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.
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Troubleshooting
