Torque sensor drift during continuous measurement and data logging
Torque sensor drift during continuous measurement and data logging
(OP)
Hello,
I'm dealing with what appears to be a torque sensor malfunction that I have not seen before. Using a rotary torque sensor to measure applied load to a rotating shaft (180 rpm), I have recorded a very consistent, gradual increase in the measured value over a period of several days. I know, due to other measurements in the system, that this is not a changing condition of the applied torque, but rather a malfunction in the rotary torque sensor. I'm hoping that someone else here has experienced this type of sensor failure or knows what might be causing this consistent signal drift. The measured equipment is known to be in steady-state condition, and measurements at other points in the system indicate that the actual applied loading cannot be changing in the way the torque sensor indicates.
This is a wheatstone bridge-type rotary torque sensor with four brushes contacting slip rings to transmit the signal from the rotating shaft to the non-rotating housing and signal wire connector. The slip rings and brushes appear to be in good shape, with no visible damage and a significant amount of brush life left.
Any help of advice is appreciated.
Regards,
Mark
I'm dealing with what appears to be a torque sensor malfunction that I have not seen before. Using a rotary torque sensor to measure applied load to a rotating shaft (180 rpm), I have recorded a very consistent, gradual increase in the measured value over a period of several days. I know, due to other measurements in the system, that this is not a changing condition of the applied torque, but rather a malfunction in the rotary torque sensor. I'm hoping that someone else here has experienced this type of sensor failure or knows what might be causing this consistent signal drift. The measured equipment is known to be in steady-state condition, and measurements at other points in the system indicate that the actual applied loading cannot be changing in the way the torque sensor indicates.
This is a wheatstone bridge-type rotary torque sensor with four brushes contacting slip rings to transmit the signal from the rotating shaft to the non-rotating housing and signal wire connector. The slip rings and brushes appear to be in good shape, with no visible damage and a significant amount of brush life left.
Any help of advice is appreciated.
Regards,
Mark





RE: Torque sensor drift during continuous measurement and data logging
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RE: Torque sensor drift during continuous measurement and data logging
RE: Torque sensor drift during continuous measurement and data logging
However you need to be systematic in troubleshooting. Measure voltage at various points with another instrument to find which component is drifting.
RE: Torque sensor drift during continuous measurement and data logging
RE: Torque sensor drift during continuous measurement and data logging
RE: Torque sensor drift during continuous measurement and data logging
MintJulep, yes the sensor was unused for an extended period.
3DDave, I did first consider temperature effects, but that seems unlikely because the sensor almost certainly would have achieved steady-state conditions after several days operating under the same conditions.
RE: Torque sensor drift during continuous measurement and data logging
RE: Torque sensor drift during continuous measurement and data logging
RE: Torque sensor drift during continuous measurement and data logging
RE: Torque sensor drift during continuous measurement and data logging
If possible change out the sensor for another sensor and see if the results repeat. If they do I would suspect the motor or monitoring system. It may just be a characteristic of your system.
RE: Torque sensor drift during continuous measurement and data logging
Doug, The output sensor is measuring torque applied to the output shaft of a worm gear speed reducer. I am also monitoring the input shaft torque (and motor power consumption) and have seen no change over a period of days. Temperature of the reducer is also being monitored and there has been no change over the same time period. If there was a change in the applied load or the efficiency of the reducer, this would have been reflected in the other system measurements, not the output torque sensor only.
I did review all of the wiring connections from sensor, to amplifier, to PCI board, to PC, just to be sure a gradually loosening wire wasn't at play. It is possible that one of these other components could be causing the issue. I will do what I can to examine their performance. Thanks for the suggestion.
I do not have another sensor with the required load rating to try in place of the current sensor.
RE: Torque sensor drift during continuous measurement and data logging
I.e., the ratings are a little optimistic.
Note also that when an individual gage is overstrained, the Wheatstone bridge will tend to hide that fact. Have you rechecked the alignment between the output shaft and whatever is providing the braking torque?
Mike Halloran
Pembroke Pines, FL, USA
RE: Torque sensor drift during continuous measurement and data logging
RE: Torque sensor drift during continuous measurement and data logging
Brian, It's possible (likely) that there is a temperature gradient from one end of the sensor to the other, but this condition would have been brought to steady state early in the test. The drifting phenomenon was observed continuously throughout the test, even when steady-state conditions surely would have been reached (days, rather than hours).
I sent the sensor for evaluation last week. Their technician noted that this type of drift is observed when the strain gage reaches the end of its useful life. They're running a bench diagnostic to confirm this. I'll post feedback when I have it.
RE: Torque sensor drift during continuous measurement and data logging
You could try testing a second unit to see if the readings drift in the same manner. If they do then I would focus on the torque sensor.
My second area of investigation is the wheatstone bridge itself and you are already having that checked. My off handed thought was if one of the resistors is drifting for some reason.
Good luck.
RE: Torque sensor drift during continuous measurement and data logging
RE: Torque sensor drift during continuous measurement and data logging
Static bench testing did not show this drift.
Electrical evaluation did not clearly identify a source of the problem.
It "sounded rough" to the technician - it made noise while rotating. This I knew.
Not all that helpful. I've started soliciting quotes for replacement.