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ADS131M08: ADS131m08 Gcal Registers

Saad Jabir
Prodigy 230 points

Part Number: ADS131M08

Tool/software:

Hello,

we use ads131m08 to measure weight. To calibrate reading , we put usually a know weight and then calculate the Cal-factor. Afterwards all readings will be multiplied by this factor.

Are Gcal registered for this purpose? or for tuning the difference between channels?.

If it is for this purpose, how can we do this if the cal-factor say around 20??

thank you for any help

Saad

  • 0
    TI__Mastermind 47925 points

    Hi Saad,

    Your Cal-factor 20 is a scale or a gain factor. Gain error, also known as full-scale error, is the difference between the actual and ideal output slopes of an ADC. For example, ideally the gain is 1, however you could get 0.02 gain error from the measured gain 0.98. 

    For the error calibration, please see the details in the section of 8.3.11 Calibration Registers in ADS131M08 datasheet. The gain calibration can be done per channel on ADS131M08. Below are the steps for offset and gain error calibration:

    Please follow this procedure for gain calibration:

    1. Perform an offset calibration. This tells you the "zero" point of the system (the "B" term in your equation y = m*x+B) 
    2. Apply a near full-scale signal (this is the "x" term in the equation). Note that this signal must be very high precision because the calibration is only as good as the calibration source accuracy. Also note that the full-scale changes depending on the gain you use.
    3. Then take several measurements and average them together. This is the "y" term in the equation.
    4. Now you can solve for "M".

    The following posts on the E2E forum could help you understand the gain error calibration:

    Please note that, after you get "M", you will have to calculate the gain setting as the contents of the GCALn[23:0] register bits and then program them into the CHn_GCAL_MSB and CHn_GCAL_LSB registers. For the example I previously mentioned, the gain setting is round(2^23/0.98) = 8559804 in decimal.

    BR,

    Dale