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About ADS1147 PGA.

Victor Lee
Prodigy 175 points
Other Parts Discussed in Thread: ADS1147

Hi,

I am using ADS1147 for measuring RTD.

I found a problem when testing the PGA, I set the Gain = 8 and the AD value of I got was 0x3E0B(it is OK), then I set the gain = 16, the AD value was 0x7C10. We can see, it is OK too.

But after sample some times(maybe 10 or 20 times, not be a certain value), the AD value change to 0x7FFF.

Well, I sent the gain setting order again, the AD value recovery to 0x7C10. The AD value change to 0x7FFF again, however, after sample some times.

Could you give me some suggestions?

Thanks!

 

  • 0
    TI__Guru* 97515 points

    Victor,


    The easiest thing you can do to debug this problem is to read the registers to detect a change in the configuration. When you start to read the part (and it reading correctly) record the register configuration. Once the problem occurs, then read the registers again to see if anything was accidentally changed. In particular, you can check the gain, the reference status, the reference input and the analog inputs.

    Another thing to do is to measure the reference and the input voltages to see if either of these values have changed. Out of curiousity, what is the input that you are measuring? Does this input voltage correspond with the code coming from the ADC?

    If you continue to have problems, I'd need some more information about how the part is used, what you are measuring, the sequence of commands sent to the device and any other setup information about how the ADC is used.


    Joseph Wu

  • 0 in reply to Joseph Wu
    Prodigy 175 points

    Joseph,

    Thanks for your suggestion.

    I will testing what you said and tell you the result.

    I have found the causation. The problem is not on the ADS1147 and is the communication between PC & MCU.

    The MCU has a function of software decodec the HART signal, and the current of my system is 4mA fixed.

    when using Optocoupler Isolated to communicate with the PC, the current excess 4mA and producte noise signal on the Current Loop.

    HART signal is add a 0.5mA current signal on the Current Loop for coummnication.

    So the MCU will decode the Noise Signal as a HART Command, and the Hart is also using the UART.

    The communication between MUC & PC was discorded by Softwar HART.

    The system was working nice after I had enhanced the Loop Current to 6mA.

  • 0 in reply to Victor Lee
    Prodigy 175 points

    Joseph,

    I have drawn a diagram for you, but I don't know how to upload it.

     

  • 0 in reply to Victor Lee
    TI__Guru* 97515 points

    When you put up a posting, go to the top and there should be a clickable link for "options". There it will allow you to upload a file.

     

    Joseph Wu