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ADS124S08: Sampling results vary depending on the ambient temperature

Atsushi Takahashi
Expert 1415 points
Part Number: ADS124S08

Tool/software:

Hi Team,

The sampling results when the ambient temperature is room(23℃) are different from those when it is 60°C.
The input point temperature and input resistance of the measurement target are the same.
It is different for all channels, and the amount of change is also inconsistent(not constant).
Are there any possible reasons?

The customer only performs Self offset calibration(SELFOCAL, 19h) at startup.

Best Regards,

  • 0
    Prodigy 20 points

    This could be due to your reference changing with temperature. On page 11 of the datasheet it shows that the internal reference has a typical drift of 2.5 ppm/C and possibly up to 10 ppm/C.

    That doesn't explain why the measurements would be so inconsistent. I'll have to think on that one. More information about the system could be helpful.

  • 0 in reply to James McMurtrie
    TI__Guru** 113765 points

    Hi Atsushi Takahashi,

    As James mentioned, it would be good to know more about the application (a schematic would be helpful) and ADS124S08 device configuration register settings.  As resistance is mentioned, it would appear that this is either a thermistor or RTD measurement.  To limit the effects of drift it is best to make the measurement ratiometric where the excitation and reference voltage are the same.   In this way the drift of the internal reference would cancel when voltage exciting thermistors, or in the case of RTDs, drift of the IDAC current(s).

    Usually what is seen with temperature measurements are drift affects due to resistors used in the ratiometric path.  For RTDs this is often the resistance used for establishing the reference for the ratiometric measurement.  The resistor should have a low temperature drift (10ppm or better per degree C).

    Another possibility is noise (EMI/RFI) getting into cabling.  This noise will average to a DC value as the ADS124S08 is an oversampling device.

    If we can get additional information we can be of better assistance.

    Best regards,

    Bob B