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Original question:

ADS1232: Temperature drift correction

ADS1232: weigh scale measurement - maximum deviation to be expected

Alen Barisic
Intellectual 1300 points
Part Number: ADS1232

Hi,

we would like to use an ADS1232 to convert the load cell of a weigh scale.
The load cell is supplied with 5V, has a nominal value of 2mV / V and therefore delivers a voltage of 10mV at full output (2,000kg).

Assuming the load cell is ideal -
What accuracy result are to be expected with the ADS1232? How many kg of deviation can be expected in the worst case?


In the data sheet of the ADS1232, tolerance ranges and maximum deviations are specified for some values and I am unsure how all these errors add up or whether I even consider all relevant parameters.
So it would be a great pleasure for me if you could perhaps offer me some support here.

Thank you in advance!

Alen

  • 0
    TI__Guru** 113765 points

    Hi Alen,

    At at a gain of 128 with a 5V reference, the full-scale range is +/- 19.5mV.  So the full-scale output of the load cell will be 10mV or about 1/4 of the of the full-scale range of the ADC so that is one limit to the total resolution.  The second consideration is the noise of the conversion (excluding any external noise pickup from EMI/RFI on cabling) which is given in the noise tables in the ADS1232 datasheet on page 5.  The peak-to-peak noise is the limit of the ADC to have a stable output result (or no flicker of the output).  

    So the best case scenario would be the peak-to-peak noise.  The total scale counts available will be the full-scale range of the load cell (10mV) divided by the best case noise (110nV from the tables at 10sps).  10mV/110nV would be about 90909 total scale counts.  A 2kg load cell with a 2mV/V sensitivity would have 90909 counts or 2kg/90909 equal to 22mg best case.  Using some averaging may result in better resolution, but remember that any external noise will affect the measurement.

    Additional error sources are linearity, offset and gain error (as specified in the datasheet in the electrical characteristics table).  Offset error can be reduced to the level of noise using the self-offset calibration feature of the ADS1232.  Gain error can be reduced by calibration.  Linearity error can be reduced by multi-point calibration.

    In the end, your noise sources will create the most error.  Most of the noise pickup will come from the cabling which will be gained up by the ADC PGA.

    Best regards,

    Bob B