Strain Gauges and Heat
Strain Gauges and Heat
(OP)
I have a problem with my strain gauge (load cell) measurements being affected by heat. I contacted the manufacturer of my strain gauge and they claimed that it is only affected 0.01% per degrees C. However, this is significantly less than what I am experiencing. Has anyone had similar problems before? Could the change in temperature (about+-2 degC) affect the wiring, which could lead to the errors?





RE: Strain Gauges and Heat
RE: Strain Gauges and Heat
Luck is a difficult thing to verify and therefore should be tested often. - Me
RE: Strain Gauges and Heat
Is your +/- 2ºC value correct? That should be negligible in the face of your other system errors. And why are you calling that "heat?" Can you even confirm that the calibration was done with +/- 1ºC?
TTFN
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RE: Strain Gauges and Heat
RE: Strain Gauges and Heat
Second, make sure the heat is not causing a non-axial loading on load cell.
Third, check your wiring. You might be reading the resistance of a large chunk of solder in a connector. Or you could have a loose connection or water.
Fourth, if this is a purchased load cell what exactly was the specification? You have to be very careful about the wording. There should be a specification for temperature affect on span and on zero. There should also be a specified operating temperature range that these values are valid.
If you made your own load cell then be aware that the 0.01%/°C value is only valid for a small temperature range. For Vishay gages they have a good paper from Vishay.
http://www.vishay.com/docs/11054/tn504.pdf
I would think that other manufacturers would be similar. (FYI - Omage gages are made by Kyowa)
ISZ
RE: Strain Gauges and Heat
RE: Strain Gauges and Heat
The strain gauge is used to measure torque. One of my problems is that the strain gauge was attached to the component by a third party company. I asked them about the possible effects of heat to the assembly and their reply was: You can expect a zero shift of up to 0,01% of the full scale per C°, and a span (gain) shift of up to 0,02% per C°. The cell is rated at 50Nm, which still doesn't explain the deviation of about 0.15Nm due to a change of only about 2 degC.
The part is cooled by water;however, as mentioned before, the water temperature varies about 1-2 degC. The part is made from aluminum, which should not be affected very much by thermal expansion.
I will double check connections, since I have not soldered them myself.
RE: Strain Gauges and Heat
it sounds like you're checking your load-cell, and calculating a difference (via your strain gauges) of 0.3%. personally i'd be happy with that correlation. how arrurately were the s/gauges located on the part (a small difference in arm could account for the difference. personally, i'd use the result to re-calc my moment arm (assume the loadcell is good, and delivering 50Nm and your calc needs to be adjusted down by 0.997 to match the loadcell).
RE: Strain Gauges and Heat
And aluminum is not affected very much by thermal expansion compared to what??? Aluminum expands 70% more than steel.
ISZ