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ADS1120: +0.9C offset measured for the range of -40C ～150C

Nicole Han
Intellectual 2230 points
Part Number: ADS1120

Hi, team, 

My customer is using ADS1120 for K-type thermocouple measurement. And they adopt below circuit from datasheet, using internal reference. RB1 and RB2 is 1Mohm. 

They found the measured temperature is always 0.9degC higher than real temperature in the range of -40~150degC. While the sensor internal temperature is 0.2deg C lower than its ambient temperature. 

Is this normal? Why does it happen?

  • 0
    TI__Guru** 112705 points

    Hi Nicole,

    The internal temperature actually in measuring the internal temperature of the device die which can be slightly different than the actual ambient temperature.  Also, any air currents flowing over the ADS1120 can affect the temperature sensor read back.  If using the ADS1120 internal temperature for the cold-junction measurement, the ADC should be at or very close to the input of the thermocouple.  

    It is also possible that there is some self-heating of the thermocouple due to the current from the pullup and pulldown resistors.  Some customers will use a larger resistance (10M) to limit the current further.

    I would suggest the customer review the material in A Basic Guide to Thermocouple Measurements for additional circuits and implementation.

    Best regards,

    Bob B