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I found a load cell and wonder if its working or damaged since the diagonal voltage is not zero with no load on it. The diagonal voltage is about two volts when I supply 5 volts. There are no stickers on the cell only a handwriting which says 200kg so I didn't have a datasheet.

My research: I read that the diagonal voltage changes usually about 2 to 10mV per supplied volt when changing the load from 0kg to full load depending on the cell. I didn't find any information about the voltage level itself only about the change.

My thoughts: However 2V seems too high because a differential OpAmp with a gain higher then 2 could be easily out of range. While a gain of 2 is too low since 10mV should be amplified with 100 or so to get proper reading on a voltage measurement device.

So the question is: What is the usual range of load cell diagonal voltages?

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The diagonal voltage is the Common Mode (CM bias) is not what is amplified, rather the Difference (lateral) voltage in a bridge type load cell.

Thus the CMRR rejects the CM voltage and the Differential Mode (DM) gain determined by R ratios in an INA (INstrument Amp) configuration of 100x is easily obtained.

The CM voltage bias only needs to be within the CM range of the INA inputs, for any given Vcc. Then the output also has a CM range where Rail-Rail type outputs are preferred in low voltage systems that need this output swing range. This depends of course on supply voltages available.

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