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Discussion in 'General Electronics Chat' started by aamirali, Nov 11, 2013.

  1. aamirali

    Thread Starter Member

    Feb 2, 2012
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    1
    Subject: Measure voltage ADS1248

    I have to measure voltage from across a variable resistor, its not RTD , its resistance varies with change in distance. So equivalent ckt looks like that I have attached. Max resistance will be 1.5K

    Now I have to measure change in resistance I have used IDAC0 of 50uA which across that resistance of 1.5K total, so give voltage 0 - 75mV. Now I have to use PGA for that but since PGA needs 0.1V away from rails.

    But I don't want to use bipolar supplies. So what I have done I have connected two fixed resistors of 1.5K each at both ends & vbias = 2.5V at pin AIN1. So voltage across Rx will not be referenced to ground. Am I doing it correct. I haven't tested it. I was thinking if it could be possibility.

    Or is there any better/right solution for this.
     
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  2. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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  3. aamirali

    Thread Starter Member

    Feb 2, 2012
    415
    1
    No there is only varaible resistance only. I placed two fixed 1.5K resistance just to make sure path don't get short, otherwise if variable resistance get low.
     
  4. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,798
    1,103
    Does it matter if the variable resistance is low? You have a current limited at a constant 50uA, so a short circuit at the resistor does no harm.
     
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