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ADS1210 query

Jasper Chong
Prodigy 10 points
Other Parts Discussed in Thread: INA128, ADS1211

Hi. I am using an ADS1210 to sample a differential voltage coming from a strain gauge. However, on every startup i am receiving different readings(etc reading before powering off is 10000, after reseting it became 10002). I have tried using self calibration or writing the full scale offset and the offset calibration registers into the chip but the results are the same. Am i missing some critical steps here? The signal input from the strain gauge have been amplified by INA128 and conditioned by a low pass filter.

I just looked through a reply on topic ADS1211 and sad to say i have tested by shorting the signals to ground and im getting consistent results on every power reset.

  • 0
    TI__Guru* 97655 points

    Jasper,

    In my reply to the ADS1211 problem (which I've posted below this sentence), I mentioned that this could be a problem with the reference settling.

    http://e2e.ti.com/forums/p/10837/42174.aspx#42174

    In that case, it is a problem with the starting reference value being off from the settled reference value. That is a case of a gain error and it is related to the FCR value and not the offset. Make sure that the reference value has settled to the final value before running calibrations.

    You had mentioned that you had shorted the inputs and gotten consistent offset results. If the FCR is off, you might not see that reflected in the OCR value. Even in your case, the change in the FCR is going to be the same as the change in your input (10002 to 10000) which is about 0.02%.

    If you are writing to the OCR and FCR registers directly, and they are the same each time, but are having issues with different readings at start up, I would look at the load cell that you are using. Disconnect the load cell and replace that with a real voltage. If you have a good precision source, measure that instead (while keeping the same OCR and FCR) to see if you have the same problem. You can post a response here.

    Joseph Wu