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ADS1248: wheatstone bridge

Brahem Khaled
Intellectual 290 points
Part Number: ADS1248

Hello

I'm using the ads1248 to mesure voltages from a wheatstone bridge

everything works fine if the power supply is not the same as the ads1248,else readings

are alterated even if I use a voltmetere the readings are wrong it seems that this configuration mess with the whole circuit .

any advice?

Ps : we are using the internal Vref

  • 0
    TI__Mastermind 20805 points
    Hi Brahem,

    I am sorry that you are having issues getting your wheatstone bridge measurement to work with ADS1248.
    In order to resolve your issue could you share some more specifics about the issues you are having?
    Could you share a schematic, the supplies you are using and maybe also the register settings?
    Could you also describe in more detail what you mean be 'readings are altered'? What are the codes you are reading and what codes would you expect?

    The ADS1248 has a limitation, that the external differential reference voltage needs to be smaller than (AVDD - 1V).
    But as you are using the internal VREF for the measurement this does not seem to be your issue.

    Regards,
  • 0 in reply to Joachim Wuerker
    Intellectual 290 points

    Hi Joachim,

    *readings are altered* I meant the values that I read and converted from the ADS were wrong (voltage).

    The problem seems be caused by the Vbias .When Vbias is disabled ,voltages values are ok.

    I used the Vbias when using the ADS as a voltmetre and the input was a calibrator and this worked fine,

    but with weathstone bridge Vbias should be off when the power supply(battery) is the same for the ADS and the bridge.

    if you can give me an explanation I would be thankful

  • 0 in reply to Brahem Khaled
    TI__Mastermind 20805 points
    Hi Brahem,

    without seeing your schematic and where you connected the VBIAS to it is hard to comment what is going wrong.
    But in general you don't use VBIAS in a Wheatstone bridge measurement configuration, at least not in the ones we usually recommend.

    You would only use VBIAS to bias a floating sensor such as a thermocouple to within the voltage range of the ADS1248.

    Regards,