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ADS124S08: Calibration time for offset and gain

Satoshi
Guru 19645 points
Part Number: ADS124S08

Is ADS124S08 have calibration (background calibration) function for Offset and Gain?

If yes, is there specification data? In particular, I hope to know calibration time.

Best regards,

Satoshi

  • 0
    TI__Guru** 113765 points

    Hi Satoshi,

    The ADS124S08 does not have background calibration.  The closest thing to a background calibration for offset is by using Global Chop which will take two conversions and average them while swapping the input channels between AINP and AINN.  Also, between conversions it is possible to initiate commands, such as the SFOCAL (self-offset calibration).  

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    Guru 19645 points

    Bob-san

    Thank you for reply,

    I confirmed ADS124S08's self calibration.(SFOCAL and SYGCAL)

    Additional question, is there specification about self calibration? 

    ①Time to complete calibration

    ②Comparison offset and gain spec by calibration or non-calibration

    Best regards,

    Satoshi

  • 0 in reply to Satoshi
    TI__Guru** 113765 points

    Hi Satoshi-san.

    The time that it takes for completing the calibration commands for the ADS124S08 is based on the number of conversion samples selected in the SYS register (which defaults to 8 samples to be averaged) for the desired data rate selected and the digital filter type selected.  For example, if the SFOCAL (self-offset calibration) is selected at the data rate of 20sps using the Low-Latency filter, it will take approximately 8 * 50ms, or approximately 400ms to complete.

    As to the calibration and usage, I highly recommend to always issue the SFOCAL command for self-offset after the ADS124S08 has been configured for the desired reference, PGA settings and data rate.  This removes the offset of the PGA and modulator and will store the value which is then subtracted from the following conversion data.

    The system calibration (both system offset and system gain) I do not recommend using in most cases.  Where the system calibration is useful is if you have a sensor that is buffered or the output altered to affect the sensor offset or gain.  This could happen from some external amplifier for example.  For the system case the calibration is also complicated by the fact that you must place a 0V input for offset calibration, and a full-scale input for gain calibration.  Applying a full-scale low-noise signal to the inputs can be difficult and can actually make the gain error worse if the signal is noisy.

    As to the ADS124S08, the device is factory trimmed for gain at the various gain settings.  Only the offset of the device needs to be calibrated and this can be done with the SFOCAL command.  After completing the self-offset calibration (SFOCAL) the offset will be within the level of noise for the PGA and data rate selected.  The gain error will be as shown in the datasheet.

    Best regards,

    Bob B