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CCS/ADS1018: Cold Junction compensation for warm PCB

Shubham Tandon
Prodigy 250 points

Part Number: ADS1018
Other Parts Discussed in Thread: ADS1118EVM, ADS1118

Tool/software: Code Composer Studio

Hello,

I am facing an issue where I am getting unusually high thermocouple readings. I believe this may be due to a large number of LEDs on the board. The board does warm up significantly...

How can I address this in software? Does the ADC read change with reference to the temperature sensor?

Unfortunately, the chip does not have thermal dissipation around the chip..

  • 0
    TI__Guru** 101305 points

    Shubham,


    I'm not sure if there's a good way to address the temperature measurement errors even in software. As I mentioned in my previous posts, the cold junction compensation would be the largest part of the error if there is self-heating of the board.

    In cold junction compensation, the thermocouple is on some cold junction that is apart from any non-isothermal area from the board. If you have many LED's on your board heating it up, this may be incredibly difficult to try to calibrate. It would depend on how long the board has been powered up, the airflow across the board, how much the power dissipation there is, how much the power dissipation varies, and the ambient temperature.

    I'm not sure how your system is set up and what the thermal properties are like. If the power dissipation is low, then you may be able to do some simple calibration. However, I'm not sure how well that would work.


    Joseph Wu

  • 0 in reply to Joseph Wu
    TI__Guru** 101305 points

    Shubham,


    I haven't heard from you in a while, so I thought I'd check on your progress on this issue. I'd noted that it would be difficult to calibrate out the temperature change with so much power dissipation on the board. Using the ADS1118EVM as an example, the processor is in the SM-USB-DIG, separate from the board and the ADS1118 is tucked into the connector for the thermocouple. If you look at this picture, you can see what I mean:

    By placing the device so close to the connector, and having no other power dissipation sources nearby, the connector is virtually isothermal to the device, and can act as an adequate cold junction.

    I'll close this post for now, but if you have other questions, post back and we can look at this again.


    Joseph Wu