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Can't get the INA122 working correctly

Ed Mauro
Prodigy 20 points
Other Parts Discussed in Thread: INA122

I'm trying to read the values off a CSLA2CD hall effect current sensor running off of a 9V regulator. The 9V regulator also drives the INA 122.

The signal off of the current sensor sits on  4.5V (no current detected) and goes up as more current passes through the device. I'm using an INA22 to try to get a differential read and then amp the signal up so I can run into my ADC (say 4.6 off the current sensor - a fixed 4.5 volts x 5G to yield a reading into the ADC of .5V). For testing I'm just using a voltage divider/pot arrangement to get the V-. And feeding the sense voltage off of the CSLA2CD into v+.  I've left the gain open (e.g., 5X). But I can't get predictable results. There seems to be 10% - 20% variations on what I read vs. what I should get. I have .10uf's across inputs, etc.

I've tried running the output of the CSLA2CD into a simple voltage divider to reduce the apparent voltage level into the INA122, but that didn't improve the situation (instead of 'seeing' 4.5 V off of the current sensor, it was seeing 2.25V).

The application is for a bicycle powered generator in a kids science museum. Any ideas would be appreciated. Thanks!!!

  • 0
    TI__Expert 7185 points

    Ed,

    Putting in a small difference voltage with a common level of 4.5V should not be a problem; however, there may be other issues that are causing you to get erroneous results.  If you can post your schematic and label all of the component values with your input voltages and your expected output voltages clearly annotated, we can help you more quickly resolve this problem.

    Thanks,

    matt

  • 0 in reply to Matthew Hann
    Prodigy 20 points

    Sorry for the delay in getting back to you (a few vacation days!). Here's the circuit. It seems to be working fine at this point. I left out the Gain resistor so it defaults to G=5. I think I would be better off if I went with a simple voltage divider with a pot in the middle for fine tuning rather then the 1N914 diode to get the voltage drop.

    7608.INA122.pdf