3 Replies Latest reply: Feb 13, 2015 4:35 AM by Wyue RSS
      • 1. Re: CN0287: Isolated 4-Channel, Temperature Measurement Circuit
        Suresha

        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

        • 2. Re: CN0287: Isolated 4-Channel, Temperature Measurement Circuit
          jtillack

          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

          • 3. Re: CN0287: Isolated 4-Channel, Temperature Measurement Circuit
            Wyue

            @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.