IDAC and resistance measurement

Discussion in 'General Electronics Chat' started by sharanbr123, Sep 29, 2014.

  1. sharanbr123

    Thread Starter Member

    Sep 29, 2014
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    0
    Hello All,

    My first post here ...

    One of the uses of IDAC (Current DAC) is mentioned as measurement of resistance.
    I am interested to know what is the method to measure the resistance using an IDAC.

    I am assuming that IDAC would drive current through a resistance and using R = V/I equation, one can measure the resistance. But I can understand that current is known but since voltage is not known, how is the resistance measured?

    Thanks a lot in advance ...
     
  2. MrChips

    Moderator

    Oct 2, 2009
    12,432
    3,360
    There are many ways to measure resistance.
    Tell us what you are attempting to accomplish and we will be in a better position to assist you.
     
  3. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    3,778
    932
    you can place the unknown resistance in a voltage divider (two resistances in series) with one resistance being a known precision value(100k for example). measure the voltage drop across the unknown and do the math.
     
  4. alfacliff

    Well-Known Member

    Dec 13, 2013
    2,449
    428
    rewsistance is measured using a known voltage. wither supplyed by the measuring instrument, or measured in the circuit along with the current. you have to have one known value to complete the measurement.
     
  5. sharanbr123

    Thread Starter Member

    Sep 29, 2014
    49
    0
    Thank you all. Basically, I am just venturing into IDAC functionality and resistance measurement was mentioned as one of its uses.
    I think I understand. The current is known & voltage drop across the resister is measured. Rest is just calculation.
     
  6. crutschow

    Expert

    Mar 14, 2008
    13,000
    3,229
    Yes you also need a voltage. After applying a known current to the resistance using the DAC you then measure the voltage across the resistance using an ADC or digital voltmeter. From that you calculate the resistance.

    An alternate approach would be to use a voltage comparator with a known accurate voltage reference, say 100mV connected across the unknown. Then you could use a successive approximation technique with the DAC current (similar to that used with many ADCs) to determine the current level through the unknown resistance that gives 100mV. From that you can calculate the resistance.
     
  7. sharanbr123

    Thread Starter Member

    Sep 29, 2014
    49
    0
    Thank you. I was thinking about the same. Use a ADC to get the voltage into digital domain and then compute R = V/I. I is known a-priori.
     
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