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Original question:

ADS1220: thermocouple temperature data read error

ADS1220: thermocouple temperature data

Ganesh Sivaramalingam
Prodigy 20 points
Part Number: ADS1220

Hi,

i'm using ADS1220 with stm32 for T-type thermocouple reading. But when the thermocouple is heated up my temp value was decreasing instead increasing can any one help me.

my reg config are 

MUX setting for AIN1 and AIN 2

GAIN 64

Data rate as 600 with normal mode.CM and BCS are on 

i didn't add any IDAC settings. 

 

  • 0
    TI__Guru** 113765 points

    Hi Ganesh,

    If you haven't done so already, I would suggest reading A Basic Guide to Thermocouple Measurements.  This guide covers a lot material that can help you successfully make TC measurements.

    Regarding the use of the ADS1220, I would recommend that you make sure that the input common-mode voltage of the TC input is within the input range of the ADS1220.  This can be done using an equal value pullup and pulldown resistors (1 to 10Meg).  There is a TC application circuit showing this in the ADS1220 datasheet.

    I would also recommend not turning on the BCS as the current can add error in the measurement, especially with any resistance in the measurement path.  The BCS should only be turned on to evaluate if sensor is degrading or if there is a broken wire.

    Are you measuring the cold-junction and compensating for voltage drop across the cold-junction?  This is explained in the basic guide.

    Do you have a schematic that you can share?  Have you verified that the TC is connected to the proper orientation for reading a positive voltage result?

    Best regards,

    Bob B