CN0287 accuracy analysis

Hi,

One of our new designs, requires us to implement RTD & Thermocouple measurement circuit.

We need to get a accuracy of better than "0.2% of FSR" over the operating temperature range of "-20°C to 60°C".

We have looked at CN0287 board & planning to use the same circuit in our board if the required accuracy is met.

The CN0287 specification says that accuracy of 0.5°C. Is this accuracy guaranteed over a specific temperature range?

For our accuracy analysis , we have identified the error introducing components as below :

RTD measurement :

  • Resistor Rref  - Tolerance & Temperature coefficient
  • ADC AD7193 - ENOB , INL , Offset error, Gain error , Offset drift , Gain drift

Due to ratio-metric cancellation,  change in excitation current & ADC reference voltage cancel out each other. Thermo-couple measurement :

  • ADC AD7193 - ENOB , INL , Offset error, Gain error , Offset drift , Gain drift
  • ADC Reference ADR3425 - Initial Accuracy, Line regulation , Load regulation, Output Noise
  • Cool Junction Compensation ADT7310 - Accuracy ( 0.5°C )

Please let us know if we have missed out any parameter in our analysis.

Also, it will be helpful if you can share any document related to accuracy analysis done on CN0287.

Looking forward to your response.

Regards,

Suresha N S

Parents
  • Hi Brandon,

    Thanks for your response.

    My apologies, I have missed out on mentioning the actual temperature measurement range in our design.

    Our requirement is to support RTD to measure temperature for -60°C to +250°C. We need to achieve 0.2% FSR accuracy which means a accuracy requirement of 0.62°C.We will try to implement the protection circuit as per your suggestion.For thermocouple our requirement is to achieve a accuracy of 0.2% over the measurement range of "-200°C to +800°C". This results in a accuracy requirement of 2°C.

    We also need to maintain the above mentioned accuracy over the operating temperature range of "-20°C to 60°C" of our board. Thus we would like to know if any accuracy analysis was done on CN0287 circuit over a operating temperature range ?

    Also, we had one query regarding your response.

    You have mentioned that the 0.5°C accuracy of CN0287 is due to the limitation of cold junction temperature measurement. We assume the accuracy of measurement in case of thermocouple is also limited by the accuracy of ADC & ADC reference voltage.

    Is there a specific reason for limiting the accuracy analysis to cold junction measurement only ?

    Regards,

    Suresha N S

Reply
  • Hi Brandon,

    Thanks for your response.

    My apologies, I have missed out on mentioning the actual temperature measurement range in our design.

    Our requirement is to support RTD to measure temperature for -60°C to +250°C. We need to achieve 0.2% FSR accuracy which means a accuracy requirement of 0.62°C.We will try to implement the protection circuit as per your suggestion.For thermocouple our requirement is to achieve a accuracy of 0.2% over the measurement range of "-200°C to +800°C". This results in a accuracy requirement of 2°C.

    We also need to maintain the above mentioned accuracy over the operating temperature range of "-20°C to 60°C" of our board. Thus we would like to know if any accuracy analysis was done on CN0287 circuit over a operating temperature range ?

    Also, we had one query regarding your response.

    You have mentioned that the 0.5°C accuracy of CN0287 is due to the limitation of cold junction temperature measurement. We assume the accuracy of measurement in case of thermocouple is also limited by the accuracy of ADC & ADC reference voltage.

    Is there a specific reason for limiting the accuracy analysis to cold junction measurement only ?

    Regards,

    Suresha N S

Children
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