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ads1248 counts during RTD open state

krishna prasad
Prodigy 80 points
Other Parts Discussed in Thread: ADS1248, ADS1220

Hi,

I interfaced three wire RTD using ADS1248. The results are ok, but I am facing problem when RTD is in open state. The circuit i have used is attached. I am not getting counts near full scale when ever RTD is in open and what ever count i am getting also decreasing slowly with time with RTD open state. Please help me in resolving this problem.

New Microsoft Office Word Document.docx

  • 0
    TI__Mastermind 23745 points

    Hi Krishna,

    welcome to our forum.

    It is not 100% clear to me how you connect the RTD to the ADS1248. Therefore it is hard for me to say what could be the problem.
    I attached a presentation that shows how we would recommend to implement a 3-wire RTD measurement using the ADS1248. It also shows what should happen in case of an open sensor condition.

    RTD Measurements.pptx

    We also have a reference design available that shows the implementation using a 3-wire Pt100.

    One additional thing I wanted to note is that you should connect pin VREFCOM to GNDA.

    If you only need to measure one RTD then our new ADS1220 might be a simpler solution for you. We also have several designs for this device and RTD measurements available.

    Regards,

  • 0
    TI__Guru* 98145 points
    Krishna,


    The problem with the RTD ratiometric measurement is that the if the RTD is burned out (or open) there's no current going to the reference resistor. If this reference is not defined, then the measurement could be variable.

    If you have a problem with a possible burned out RTD, I would suggest turning on the internal reference, then turning on the burnout current sources and making the measurement each time you want to check the RTD status. That should work to test the RTD.


    Joseph Wu