How to read current scale on analog meter

Discussion in 'General Electronics Chat' started by Circuits123, Aug 28, 2014.

  1. Circuits123

    Thread Starter New Member

    Dec 7, 2012
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    Could someone explain or point me to a good resource for understanding how to read the scale for measuring current on an analog meter? Here's a picture of the meter I own: http://fs01.enter.ru/1/1/500/73/162877.jpg

    I've searched the web and YouTube but I'm still confused.
     
  2. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    the set of numbers and scale marks(in black) which are close to, and right below the uppermost ohms scale will apply to all dc amp readings. your meter selection switch indicates which of the three sets of numbers to use. in your case the scale ending in 25 will be used for all settings except the 50 microamp position.
    the red scale line would be read from if measuring AC. notice that your selector switch has all AC settings printed in red? also notice that the printed words on the scale at either extreme which point to triple stacked number region between the downward pointing black scale and upward pointing red scale.
     
  3. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    Good question, there is a lot going on in that scale.

    On the left side it shows what scales go with what readings. The very top is for resistance, below is DC volts (DCV) and amps (A), and the AC Volts (ACV).

    The meaning of the tick marks is defined on the right side. The ticks go 0 to 100% (marked 0 thru 10), so for the 50 uA scale you read the ticks from the 50 scale, and for the 2.5 mA, 25mA and 2.5A you use the 250 scale and mentally place the decimal point where needed.

    The mirror is to remove parallax which happens when you look at the needle at an angle. Move your eye till the pointer covers it's reflection and you have no parallax, so take the reading you see that way. I close one eye for this.



    [​IMG]
     
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  4. crutschow

    Expert

    Mar 14, 2008
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    The 10V AC range has its own (red) scale to compensate for the error form the diode drop of the internal rectifier. The error is so small for the higher ranges that the same scale can be used for AC or DC.
     
  5. ian field

    Distinguished Member

    Oct 27, 2012
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    Analogue meters are best for fast moving values when the prevailing amplitude trend is more important than the absolute value when the pointer slows down long enough to see where its at.

    A DMM wins when a precise value needs to be read - unless its a rapidly changing value that makes the numbers spin like the wheels in a fruit machine.
     
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  6. Circuits123

    Thread Starter New Member

    Dec 7, 2012
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    Thanks. That helps. But I'm still a little confused about the range settings. They go: 50uA, 2.5mA, 25mA, 0.25A

    Am I correct that in decimals that would be .000005A, .0025A, .025A, and .25A ?

    So say like the needle is pointing to the 250.... Sorry, I don't get the last part "mentally place the decimal...."
     
  7. ian field

    Distinguished Member

    Oct 27, 2012
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    A mA is 1/1000 of an A, so the decimal point moves over 3 places - from mA to uA it moves the same amount again.

    There are multiplier charts that can be found online for capacitor values, they can be a handy guide for mA & uA too.
     
  8. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    The "mirror" between the scales is there to avoid reading errors.
    Take a view at the following video to learn more about it:



    Bertus
     
  9. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    Correct... except the last is 2.5A not .25. I suspect a typo.

    Say you were measuring a current of 1A. On the 2.5A scale the needle would point to the tick labeled "10". Now you know the max on that scale is 2.5 not 250, so you mentally shift the decimal point so 10 becomes 1.0.

    Also, the better (less destructive on your meter) is to set to the highest (2.5A) scale before connecting. Then you can move the switch to the lower (more sensitive) ranges till the pointer is not off to one side.

    (Sorry for the late reply: I lost your post!)
     
  10. studiot

    AAC Fanatic!

    Nov 9, 2007
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    That's a good reply from ernieM (and some others), just a couple of extra points.

    All the scales, except the resistance read from left to right.

    The resistance scales read the other way (right to left).

    You should try to choose a range that places the pointer in the upper half of the scale.

    But always start with a high range and work down, analog meters can be easy to damage.
    So to measure on the 50 micro amp range, start with the meter set to the 0.25 amp range before connection
    Connect to the circuit (or switch it on)
    then switch the meter down through the ranges until the pointer is reading in the upper half.

    Always return the meter to the off position or the volts postition after use.
    This will prevent the meter being inadvertently misconnected and burning out on next use.

    The socket labelled output has a capacitor in series with the AC meter to measure dB on the dB range, it does not say but these are usually 0dB= 1V RMS into 600 ohms.
     
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