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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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  • Hi Suresha N S,

    CN0287 system performance varies under different type of sensor. The 0.5°C is the accuracy for thermocouple due to the limitation of Cold Junction Measurement Accuracy from ADT7310. We actually have ADT7320 with 0.25°C accuracy for performance upgrade. I’m pretty sure that the board could get the accuracy of 0.16°C (Calculated from 0.2% of “-20°C to 60°C”) very easily if using RTD to be the sensor.

    One thing need to pay more attention when using RTD: The protection components will generate small leakage current that cause difference between the current going through the RTD and the current finally going through reference resistor and generate additional error as calculated in the circuit note. I would highly recommended you to select the low leakage TVS and diodes if the protection function is necessary. The TVS(PTVS30VP1UP) and clamping diodes(BAV199LT1G) are recommended unless you could find other components with lower leakage.

Reply
  • Hi Suresha N S,

    CN0287 system performance varies under different type of sensor. The 0.5°C is the accuracy for thermocouple due to the limitation of Cold Junction Measurement Accuracy from ADT7310. We actually have ADT7320 with 0.25°C accuracy for performance upgrade. I’m pretty sure that the board could get the accuracy of 0.16°C (Calculated from 0.2% of “-20°C to 60°C”) very easily if using RTD to be the sensor.

    One thing need to pay more attention when using RTD: The protection components will generate small leakage current that cause difference between the current going through the RTD and the current finally going through reference resistor and generate additional error as calculated in the circuit note. I would highly recommended you to select the low leakage TVS and diodes if the protection function is necessary. The TVS(PTVS30VP1UP) and clamping diodes(BAV199LT1G) are recommended unless you could find other components with lower leakage.

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