conductivity with a multimeter

Discussion in 'General Electronics Chat' started by Tim Ostrom, Oct 26, 2008.

  1. Tim Ostrom

    Thread Starter New Member

    Oct 26, 2008
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    Does anybody know how to quantitatively test the conductivity of different concentrations of salt water using a digital multimeter?

    Thanks,
    Tim Ostrom
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Conductivity is the inverse of resistance. One way to measure it is to apply a small AC voltage across the sample with a known resistor in series. Measure the voltage across the electrodes and get current by Ohm's law.

    Using AC prevents building up deposits on electrodes that will throw results out. If you can arrange to use a cuvette with an interior area of a cm square or some known multiple, then the data are more easily presented in mhos/cm sq.
     
  3. jamers

    Member

    Jan 24, 2008
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    Beenthere has an excellent solution.

    Remember though that your results are going to be temperature dependent, so that if you do have not have a set temperature for your readings your results are going to be incorrect.

    Any air is going to throw off your conductivity readings as well.
     
  4. studiot

    AAC Fanatic!

    Nov 9, 2007
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    I recall a physics experiment where we used the output from a signal generator, and measured the AC current across the resistor at various frequencies.

    A plot of the resistance against frequency was then extrapolated back to zero frequency to obtain the DC value.
     
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