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A tip for current measurement with DMM ?

Discussion in 'Electronic Repair' started by N Cook, Jan 19, 2008.

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  1. N Cook

    N Cook Guest

    Can anyone improve on the following especially reducing, even further, the
    chance of mistakingly using a meter set for current monitoring on live kit ,
    thinking you are measuring voltage.

    Assuming others here are like me, rarely use the current function of a
    DVM/DMM.
    Leave a gummy bright or contrasting sticker over the ammeter socket of the
    meter. When transfering the red lead to that socket then transfer the label
    to the function or on/off switch.

    The ideal would be some sort of mechanical interlock but I cannot see how.
     
  2. My Fluke says 'lead' on the display when you change. Hasn't stopped me
    blowing a fuse though. ;-)
     
  3. Some DMMs -- such as my Fluke -- have a beeper that sounds when the switch
    is set to measure voltage, but the cables are plugged into the current
    jacks. (The opposite situation doesn't need a warning.)
     
  4. Hi,

    Have a look at

    <www.gmc-instruments.com/english/produkte/metrahi2.htm>

    This DMM (obviously discontinued) and other types of that line
    of GMC DMMs have a so called "Automatic Blocking System":
    depending on the measuring range only the corresponding inputs
    can be used - the other ones are blocked.

    I don't know if Gossen Metrawatt's DMMs still have this feature.

    HTH

    Reinhard
     
  5. Meat Plow

    Meat Plow Guest

    Same here. I've blown a few fuses in my 77.
     
  6. N Cook

    N Cook Guest

    Its not the blowing of a meter fuse that I'm concerned about. Its shorting
    some expensive bit of otherwise working kit that I'm wary of.
    I've not done it for a long time but there could so easily be some time in
    the future, probably pushed for time, and there will be a big flash and a
    bang.
     
  7. Ron(UK)

    Ron(UK) Guest


    I am in the happy position of having several decent meters, one of which
    I use exclusively for current measurements. It has croc clip leads.

    It`s very rare that my favourite Flukey gets switched to amps - So
    there`s your answer, buy another meter just for current, fit it with
    croc clips to remind you do to go poking around circuit boards with it

    Ron(UK)
     
  8. N Cook

    N Cook Guest

    I take it the 2 red rings on the lower line are shutters that slide away
    when the probe plug is pushed into the relevant socket.

    It still leaves the possibility of thinking (or not thinking) that the DMM
    is , per usual, set for measuring voltage but is still set for current.

    So far, the only retrofit add on I can think of, is a buzzer activated on
    inserting the probe plug in the current socket and beeps continuously until
    removed.
     
  9. N Cook

    N Cook Guest

    That seems the easiest solution, with permanent blanking off the current
    sockets of the one used for Vac & dc ,R , and D test only. I will see if my
    old Beckman or whatever it is is still working order.
     
  10. Eeyore

    Eeyore Guest

    Some Fluke models beep at you if you select a voltage range with the probe still
    plugged into the current socket.

    Graham
     
  11. AFAIK the input sockets for measuring current are blocked mechanically
    when the function/range selector is switched to voltage or resistance
    measurement (and vice versa): it isn't possible to insert test leads
    into the blocked sockets.

    At the same time you can't switch to voltage (or resistance)
    measurement if the test leads are still plugged into the current
    measurement sockets.
    No, it wouldn't be possible to turn the function/range selector switch
    to any voltage measurement range.
    IMHO this wouldn't be necessary any more.

    Regards

    Reinhard
     
  12. N Cook

    N Cook Guest

    The point of my post/query was that someone, like me, using the same DMM day
    in day out, 99.99 percent of the time for other than current, may accidently
    go to use this meter , still set in amps mode, for measuring volts , just
    because it is so ingrained in using it for such purposes.

    Anyway, potential pitfall solved using Ron(UK) technique in this thread.
     
  13. N Cook

    N Cook Guest

    A 5 minute job and peace of mind.
    Fluke 77 with hot melt glue down the 2 current sockets and a dollop on the
    rotating function switch surround. so it cannot be turned to A dc or ac.

    A dollop of hotmelt in the "volts" socket of the old meter and a 2 croc-clip
    ended leads. instead of probes, so very unlikely to absent-mindedly use use
    that one in volts test mode.
     
  14. Ron(UK)

    Ron(UK) Guest

    Or just use some pvc tape, avoid ruining a meter, neater and cheaper, or
    if you want an elegant solution, you can buy blanking plugs in red and
    black to fit 4mm banana sockets.


    Ron(UK)
     
  15. Actually, it might. If you have leads plugged into the voltage inputs
    and are attempting to measure current in a high voltage system such as
    a laser power supply, the DMM will likely smoke when power is turned on. :(

    --- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
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    Important: Anything sent to the email address in the message header above is
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  16. Jamie

    Jamie Guest

    What are you saying? You blew up your meter? :)
    Get a industrial fluke.
     
  17. Ryan Weihl

    Ryan Weihl Guest

    but have you considred a clamp-on probe to measure current.
    Fluke makes one, forgot model nbr, matches to a particular meter.
    The output would be a voltage you can measure with the DMM
    that prevented us blowing ddm when measuring currents

    --
     
  18. Ross Herbert

    Ross Herbert Guest

    :Can anyone improve on the following especially reducing, even further, the
    :chance of mistakingly using a meter set for current monitoring on live kit ,
    :thinking you are measuring voltage.
    :
    :Assuming others here are like me, rarely use the current function of a
    :DVM/DMM.
    :Leave a gummy bright or contrasting sticker over the ammeter socket of the
    :meter. When transfering the red lead to that socket then transfer the label
    :to the function or on/off switch.
    :
    :The ideal would be some sort of mechanical interlock but I cannot see how.


    Gossen Metrawatt meters have the interlock function. If you have the RED lead in
    the normal V/Ohms socket the current measurement sockets are blanked off with a
    red plate. You can't select the current ranges on the range switch until the RED
    lead is unplugged. If you have the RED lead in one of the current measuring
    sockets (mA or A) the range switch can't be moved to any other position. Of
    course this doesn't stop you from trying to measure voltage while it is set up
    for current measurement but I find that I always check for range setting before
    connecting to equipment and because the switch won't move to any other position
    this has always prevented mishaps.
     
  19. But just how accurate are they when measuring small DC current?
     
  20. James Sweet

    James Sweet Guest


    I use the current measurement frequently, the only time I've had trouble is
    going back to voltage measurement after using current and even then it's
    rare and results only in a blown fuse.
     
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