Electronic – Load cell and amplifier

amplifierinstrumentationload cell

I'm trying to get a reading from a Digi-Star load cell.
I'm using the INA122 instrumentation amplifier, the schematic is attached.

Nothing complicated, I connect the cell output directly to the ina122 inputs, and I use a low gain (10K Rg).
Single power supply, 5V, to power the amplifier.

The problem is that at the output I have about the supply voltage.. about 4,8 V.

I used the same schematic as the one in the datasheet..
I don't understand why this behavior.. Any idea?
Thanks
load cell

EDIT: problem solved!
I used the same voltage for the amplifier and the load cell, and I added a potentiometer to control Vref. Thanks to Andy for his advices!
enter image description here

Best Answer

The regulator is the problem - you are exciting the bridge with 12 volts and this means that the typical voltage on the bridge output (to ground) is half this value at 6V.

You are running the chip from 5V and so I suggest you feed the bridge power connection from 5V. The next problem you will have is that the offset (reference) pin of the INA122 is connected to ground and this should ideally be connected to half the power rail of the INA122. This then accommodates a bipolar input range from the bridge. See figure 5 of the data sheet.

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