Measuring small resistance change

Discussion in 'General Electronics Chat' started by Dritech, Dec 6, 2015.

  1. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
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    Hi all,

    When measuring small changes in resistance, which from the two methods shown below is the most accurate/reliable in practice?

    - Method 1 is the kelvin four wire measurement technique
    - Method 2 is the Wheatstone bridge

    I personally think method 1 is the most accurate/reliable since in method 2 all resistance must be perfectly equal and it is more prone to temperature changes etc. Also, if the leads to the sensor are long, it will affect the accuracy of the measurement.

    What are the advantages of Method 2? Why is Method 2 more used than Method 1?

    Any kind of help would be highly appreciated.

    [​IMG]
     
  2. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    I would disagree about the 4 wire technique being less common. Most every quality bench meter has 4-wire ohm measurement capability.

    Not so common as a teaching method but very common as a practiced technique.
     
  3. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    Also, in a true Wheatstone bridge, you have a galvanometer across the bridge, not a voltage measurement. Any current flow is then detected. A load cell / strain gauge is simply measuring the voltage across the bridge.

    Finally, a 6-wire strain gauge setup accounts for voltage changes with temp if the sense wires go to the ref of an instrument amplifier and maintain constant voltage.
     
  4. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    What method to choose depends on what you are doing?

    Why are you measuring resistance? Is this some sensor or just validation parts before nsertion? What value resistor, since as the resistance becomes much greater than the wiring resistance kelvin is less and less necessary.

    Do you want to know if it changed or how much it changed?
     
  5. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
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    Thanks for the replies.

    So what are the advantages (if any) of using a bridge when compared to 4 wire technique?
     
  6. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    It depends on the tools you have available or what your goal is. Please describe.
     
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