Accurate DMM reading?

Discussion in 'General Electronics Chat' started by aguywithfeet, Jul 7, 2014.

  1. aguywithfeet

    Thread Starter New Member

    Jun 6, 2014
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    I am trying to verify that an electric meter pulser is putting out pulses correctly. My literature says that it puts out a 500 milisecond pulse, dry contact closure, it is being supplied with 10vdc on the common. I believe it is caled a Form A pulse??

    My concern is that my Digital multi meter is not seeing that quick of a pulse and that i am simply missing them, due to the DMM not "refreshing" quick enough. I have no clue though, could just be a broken pulser.

    Any input is appreciated......unless its disparaging....nobody likes that kind.
     
  2. Sensacell

    Well-Known Member

    Jun 19, 2012
    1,124
    266
    DMM's are pretty slow, not much use for time varying signals.

    The simplest way to verify this pulse would be to connect an LED and resistor to the output.
     
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  3. aguywithfeet

    Thread Starter New Member

    Jun 6, 2014
    13
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    Cool thanks, I didn't think of that. Great idea
     
  4. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,494
    2,363
    500ms is fairly long, should be sufficient for a meter to at least respond, some meters like the Fluke have a linear bar display below the digits, this reacts at a faster rate than the digit display and can at least give a rough idea of output.
    Max.
     
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  5. Papabravo

    Expert

    Feb 24, 2006
    10,135
    1,786
    What kind of DMM do you have, and can you explain what you thought your DMM would actually do with a pulse input? Read the peak value perhaps, or read some kind of average, or maybe some other possibility. The feature you want might actually be there without you being aware of it. Unless it is a $3.99 model from Harbor Freight, accuracy is unlikely to be a problem.
     
  6. inwo

    Well-Known Member

    Nov 7, 2013
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    315
    Does your meter have a period setting and counter?

    That would seem the most helpful.

    The actual pulse length may not be important.
     
  7. wayneh

    Expert

    Sep 9, 2010
    12,083
    3,021
    Of course the proper tool is an oscilloscope. Seeing is believing.
     
  8. alfacliff

    Well-Known Member

    Dec 13, 2013
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    are you using your dmm on ac, or dc? ac should respond, vootage indicated might not mean anything, but presance of pulses should be indicated as a jump in voltage.
     
  9. aguywithfeet

    Thread Starter New Member

    Jun 6, 2014
    13
    0
    Sorry, I have a pretty nice Fluke. I guess the issue ended up being the pulser. I did read a pulse on another one. The question just came up in checking and before I threw the pulser out I wanted to be sure. I am a commercial electrician by trade but I am having to learn as I go about these "low voltage" issues.
    I'll have more questions, so bolo. :)
     
  10. snav

    Active Member

    Aug 1, 2011
    100
    10
    I was going to say, my fluke 117 has this spec for continuity

    Beeper on < 20 Ω off > 250 Ω; detects
    opens or shorts of 500 μs or longer.

    And the 112 it replaced was specced at 250uS
     
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