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ADS1220EVM: T-type thermocouple measurement using ADC1220EVM

Bhavya V
Intellectual 525 points
Part Number: ADS1220EVM
Other Parts Discussed in Thread: ADS1220, ADS1120, ADS1118

Hi, 

We need to measure the temperature using T-type thermocouple. This thermocouple will be used in medical application and will be touching internal of human being. 

We are using MCP9601 from microchip which is causing issues when the thermocouple is touched at the tip, open air measures fine. Even saline by itself is fine but as soon as I dip my hand with the thermocouple in saline, short circuit triggers. 

We have used LTC2983 before and that doesn't cause any such issues by touching. But due to cost an availability issues we moved away from it. 

I think for LTC2983 one of the thermocouple lead was grounded design vise, it was single ended so we didn't see any issue. 

I am planning on switching to TI module, which based on availability would be ADS1220 or ADS1120. 

I want to buy the eval board for ADC1220 and test it with thermocouple by touching the tip dipping it in saline etc.

Will I be able to hook up thermocouple to  ADC1220EVM and test it straight away? Its better I ask and then order, hence the question.

If you think its not a good choice please suggest the part which is available to purchase for EVM and product build.

 

Thank you,

Bhavya

  • 0
    TI__Guru** 112895 points

    Hi Bhavya,

    The MCP9601 and the LTC2983 are both direct temperature to digital converters.  TI does not have such a device at this time.  The ADS1220 can be used for measuring temperature but will require cold-junction compensation independent of the ADC.  The ADS1220 measures a voltage that must be converted to a temperature.  There is a code library for making these measurements but this will need to be run on the micro.  The EVM is equipped to connect a thermocouple, but the GUI will only output a voltage which would then need to be converted by hand to temperature.  Another option would be the ADS1118, but this would also require a conversion external to the device.  You can see how these devices would work in an application by reviewing the material in A Basic Guide to Thermocouple Measurements.

    There is a concern as to why the MCP9601 didn't work.  The same issue could happen with a different device as well, so it would be good to understand why the device shorted when touched.

    Best regards,

    Bob B

  • +1 in reply to Bob Benjamin
    Intellectual 525 points

    Got it Bob thank you for the response. I'm working with Microchip for further investigation for MCP9601. But for now we decided to use MCP9600 which does not provide SC & OC output, the system works fine now.