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Original question:

ADS124S08: Universal sensor reading

ADS124S08: ads124S06

osman
Prodigy 30 points
Part Number: ADS124S08

I'm making some measurements with ads124S08evm.
It is stated in the datasheet that thermocouples can be measured on the ADS124s08evm using two different topologies, both via j7 and j8.
In one of these two topologies, the thermocouple voltage was measured by connecting with resistors R71 and R72, while in the other, the thermocouple voltage was applied to ADS124S08 without using a resistor set.
Which of these topologies is the most correct? Can you comment comparatively?

Thanks.

  • +1
    TI__Guru** 113765 points

    Hi Osmon,

    I would suggest looking at the various circuits and information in A Basic Guide to Thermocouple Measurements.  There are even more types of possible connections besides the two mentioned.  Both EVM methods establish the thermocouple to be within the ADC input measurement range.  The pullup/pulldown method allow for easy detection of open circuit detection.  But this method also creates some self-heating as current flows through thermocouple.  Using the VBIAS allows for the use of the Burnout Current Sources (BCS) for open circuit detection while also establishing the input voltage to be biased at AVDD/2.  So for the connection type there is no right or wrong answer and what is actually implemented becomes more system dependent. 

    More important than the biasing method is the cold-junction compensation.  The thermocouple measurement is highly dependent on the accuracy of the cold-junction temperature measurement.

    Best regards,

    Bob B