CN0287: Isolated 4-Channel, Temperature Measurement Circuit

For questions or comments regarding CN0287, please reply to this post.

  • 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

  • Hello,

    Is there any reference on how the CN0287 demonstration software is using / configuring the AD7193? Specifically, it is not clear how the AD7193 should be configured for the different sensor types. Could someone write a brief description such as:

    For 2 wire RTD measurements, the AD7193 will be configured as follows...

    For 2 wire thermocouple measurements the AD7193 will be configured as follows....

    etc

    This information would make the reference design much more useful.

    Any help will be greatly appreciated.

    -Jonathan

  • @Hello Sir

    We did the CN0287 evaluation software by Labview and I attached the snapshot of default configuration used by Evaluation software for different type of sensor.

    All the configuration for different types of thermocouples and RTDs are almost the same except the gain setting which is depend on the output signal scale. The gain were decided by the type of sensor and the temperature range of the application. We prefer to occupy at much of dynamic range as possible by setting the biggest reasonable gain to process the signal.

    With best regards,

    Willie.

  • This circuit has been implemented in a design that is interfaced with a proprietary CPU. Having been given the task of writing the driver, I'm trying to understand how to perform temp measurement with a type K thermocouple. The "Default Configuration.png" is helpful in configuring the devices but I'm not sure how to apply the data read from the ADT7310 and the AD7193 to compute the temperature at the thermocouple end. Can someone walk me through the steps/equations or point me to a tutorial on how to accomplish this?

    Any help would be greatly appreciated,

    Nick

    •  Analog Employees 
    on Jul 6, 2015 10:58 PM over 5 years ago

    Here is a tutorial on how to compute the thermocouple temperature.

    http://www.analog.com/media/en/training-seminars/design-handbooks/temperature_sensors_chapter7.pdf

    And here is some extra information relating to thermocouples.

    Reference Design Spotlight on Thermocouple Temperature Measurement Systems | Analog Devices