Use of a VOM or DMM

Discussion in 'The Projects Forum' started by Meter man, Apr 16, 2012.

  1. Meter man

    Thread Starter New Member

    Apr 3, 2012
    2
    0
    Hello All,

    Q: Using a VOM or DMM, how can you make a voltage measuring device like an oscilloscope monitor a dry relay contact without fear of damaging the relay contact?

    I'm thinking a DMM has a high internal resistance. The DMM has its own internal voltage. This would allow a technician to make a voltage measurement without damaging the dry contact.

    Thanks,
     
  2. #12

    Expert

    Nov 30, 2010
    16,343
    6,827
    Set the meter on, "ohms" and connect it in series with the contacts. Then connect the oscilloscope to the remaining lead of the meter and the remaining connection to the contacts.

    Set the 'scope to show deflection when DC arrives at its probe. Some meters use 9 volts. Some use less than half a volt.
     
  3. DickCappels

    Moderator

    Aug 21, 2008
    2,661
    632
    (If I understand the question)

    A: Apply direct current to the relay contacts and measure the voltage across the contacts with a voltmeter set on the appropriate scale (usually the most sensitive scale).

    If this does not answer your question, please provide more information about your application.
     
  4. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    4,771
    971
    What do you need the oscilloscope for?
    Simply using a DMM set to ohms (turn on the beeper too) will allow you to easily test the state of a relays contacts. Put the leads on C and NC and the DMM will beep when the relay is not energized.. But the leads on C and NO and the DMM will beep when the relay is energized..
     
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