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ADS1120: Thermocouple measurement offset calibration

Kartik V63
Prodigy 30 points
Part Number: ADS1120

Hello guys,

So I am using ADS1120 to measure the thermocouple temperature. As I was referring to the manual I came across the section 9.2.1.3 Application curves which speaks about a system offset calibration performed to translate Vtc to 0V. Can anyone explain what kind of offset calibration was it? As I am trying to measure the K type thermocouple temperature, I get some absurd values after I perform the cold junction compensation as mentioned in the manual.

My ambient temp is 22.5 deg C and for testing purposes I am measuring an object with 30 deg C temperature (this is the hot junction).

Can anybody help me with this?

Thanks,

Regards,

Kartik

  • 0
    TI__Guru** 113765 points

    Hi Kartik,

    First I would suggest review the TC information found in this guide:

    http://www.ti.com/lit/an/sbaa274/sbaa274.pdf

    Before digging too deep into system calibration I would suggest looking to verify that there are not other issues that need to be addressed first.  You can look at device offset of the ADS1120 and correct that first.  You can adjust out the offset by following the information on page 30 of the ADS1120 datasheet in section 8.3.12.  Subtracting out the offset from the TC measurement should bring you very close to the actual temperature.  If it does not, you should verify that the CJC is correct.  You have not stated how you are measuring the CJ.  Also, the CJ should be thermally isolated from other temperature effects on the PCB.  In other words, you cannot assume that the ambient temperature is the same as the cold junction temperature.

    If you share more details on your measurement for the TC and the CJ, the calculation used to determine the temperature, the schematic and the PCB layout I may be of additional help.

    Best regards,

    Bob B