Reading a multimeter - units

  1. I am trying to make sure that the data I read off my multimeter has the right units.

    I have a multimeter that is a similar model to this one:
    http://www.tequipment.net/BK2703B.html
    You can enlarge the image to see the settings.

    When I measure AC current, my result says "2.95" when the setting is on 20m/10A, using the mA and COM ports (this model doesn't seem to have AC current, but the DC current has the same label). Is it 2.95 milliamperes?

    Thanks.
     
  2. jcsd
  3. I hate autoranging.

    Put a known resistor on battery (know current) and see what the meter says.
     
  4. This is odd. I'm just using V = I*R, with .235 V, 38.3 ohms, and it should be .00671 amps. I put the meter on 20m/10A, and it spit out 2.71. That's still in the milliamp range, but I'm just not sure if I want to trust it. I'd hate to have done all the work getting these results, just to use the wrong units.

    Does anyone know for sure how to interpret the results? I hope AC doesn't have any affect on it.
     
  5. Redbelly98

    Redbelly98 12,020
    Staff Emeritus
    Science Advisor
    Homework Helper

    It looks like the impendance of your meter is comparable with 38 ohms, when in 20mA mode. That would reduce the current you actually get.

    Try a 9V battery with a 1k or 10k ohm resistor and see what you get.

    EDIT: I just realized something. 2.71 A is way over the range of a 20mA range setting. So it must be 2.71 mA ... but checking things out by doing a measurement like you are doing is definitely a good thing, it helps you learn about and become more familiar with your meter.
     
    Last edited: Jan 3, 2009
  6. russ_watters

    Staff: Mentor

    2.95 should be mA, but I would think that since the meter doesn't measure AC current, it is just a bogus reading.
     
  7. The one I linked to isn't the model I have - mine does measure AC (it has a switch for Ac/DC).

    After some more testing it seems that any of the settings that are labeled with an 'm' like 20m or 200m are measured in milliamps. Thanks for your help.
     
  8. MATLABdude

    MATLABdude 1,724
    Science Advisor

    I'd recommend having a read-over of the manual for your particular multimeter:
    http://www.bkprecision.com/

    (That's assuming it's actually manufactured by BK Precision)
     
  9. I've looked over the manual - no help in there. I think I'm safe to assume it was .00295 Amps.
     
  10. this
     
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