reverse polarity protection for voltmeters

Discussion in 'The Projects Forum' started by eceeng, Sep 12, 2007.

  1. eceeng

    Thread Starter Member

    May 8, 2007
    10
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    what is the best way to protect a voltmeter or VOM from the damages brought by connecting the device in the wrong polarity?
     
  2. Neo1130

    Member

    Sep 3, 2007
    13
    0
    MOST of them should have it built in if I am not mistaken...
     
  3. recca02

    Senior Member

    Apr 2, 2007
    1,211
    0
    diodes i guess.
     
  4. techroomt

    Senior Member

    May 19, 2004
    198
    1
    if you are talking digital display, then the meter will just read the value in negative notation.

    the analog display type, or vom, will attempt to deflect the needle below zero and can damage the movement. they are not protected that i am aware of. the exact reason why techs should be aware of the "expected voltage polarity" reading before inserting leads - always a good idea. so the best protection here is knowledge.

    however, in the event a negative going needle is observed, a quick removal of the probes will lessen the likelyhood of movement damage.
     
  5. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    A modern instrument has built-in overvoltage protection and is insensentive to applied polarity. It just gives the reading and wheather it was positive or negative with respect to the common kead.

    When you say VOM, I think of Simpson 260. It had P-poor overvoltage and you just watched the needle bounce off the left stop when testing the wrong polarity.
     
  6. Neo1130

    Member

    Sep 3, 2007
    13
    0
    Didn't they also have circuit breakers in them that would pop in this certain condition?
     
  7. Distort10n

    Active Member

    Dec 25, 2006
    429
    1
    My Fluke has fuses; although I forget the amperage rating.
     
  8. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    The fuses are in the current measuring circuit. 350 ma and 10 amps for my Fluke 23 (both are original).
     
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