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

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  • Hello Willie,

    Thanks a lot for detailed response.


    We had one query with regards to your response.

    Our operating temperature range in -20°C to +60°C. Thus the maximum variation from 25°C (Considered as ambient temperature of our board) is 25-(-20)= 45°C.

    Thus in thermocouple calculation, ADR3440 (8ppm) temperature change will generate 45 x 8 = 360ppm variation. This reduces our final effect of reference on accuracy to 0.72°C & RMS accuracy value will be 0.87°C.

    Similarly, in case of RTD, resistor variation will reduce to 10 x 45 = 450ppm. This will increase RTD accuracy to to 0.15%.

    Is our calculation correct ? Please comment.

    Also, we are planning to do a complete accuracy analysis for our design based on CN0287,including ADC parameters such as INL, gain drift ,offset drift etc.

    Will it be possible for you to review our accuracy analysis document ? This would really help for us to go ahead with the design.

    Regards,

    Suresha


Reply
  • Hello Willie,

    Thanks a lot for detailed response.


    We had one query with regards to your response.

    Our operating temperature range in -20°C to +60°C. Thus the maximum variation from 25°C (Considered as ambient temperature of our board) is 25-(-20)= 45°C.

    Thus in thermocouple calculation, ADR3440 (8ppm) temperature change will generate 45 x 8 = 360ppm variation. This reduces our final effect of reference on accuracy to 0.72°C & RMS accuracy value will be 0.87°C.

    Similarly, in case of RTD, resistor variation will reduce to 10 x 45 = 450ppm. This will increase RTD accuracy to to 0.15%.

    Is our calculation correct ? Please comment.

    Also, we are planning to do a complete accuracy analysis for our design based on CN0287,including ADC parameters such as INL, gain drift ,offset drift etc.

    Will it be possible for you to review our accuracy analysis document ? This would really help for us to go ahead with the design.

    Regards,

    Suresha


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