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Measuring DC amps with a digital multimeter

krishunt

Nov 10, 2018
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Please help me understand how to use my digital multimeter to measure amps. There are two scales on my meter for measuring DC amps: 200 mA and 10 A. When I measure a current with the multimeter set to 200 mA, I get about 10 mA, but when I set the scale to 10A, it says 0.10 A. Since there are 1,000 mA in 1 A, why doesn't it say either 10 mA / 0.01 A, or 100 mA / 0.10 A? I don't get it.
 

Minder

Apr 24, 2015
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I suspect the 10ma reading is too low for the resolution of the 10amp range.
That is why you have a Ma range.
M.
 

davenn

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Sep 5, 2009
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Hi
Welcome to EP :)

When I measure a current with the multimeter set to 200 mA, I get about 10 mA, but when I set the scale to 10A, it says 0.10 A. Since there are 1,000 mA in 1 A, why doesn't it say either 10 mA / 0.01 A, or 100 mA / 0.10 A? I don't get it.


possibly / probably because the 10A range cannot measure 10mA accurately
It probably can only read in the minimum of 100mA accuracy .... that would be the obvious answer :)
hence why it is important to use the correct range for the expected value

You will also probably find that a high voltage scale will have the same problems reading a very low value voltage


The 10A range is probably limited to one decimal point value
as would high voltage ranges



Dave
 

krishunt

Nov 10, 2018
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If that were the case, then it would simply read zero, not fluctuate between 0.10 and 0.11 amps, which is exactly one order of magnitude away from being quite accurate.
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Jan 21, 2010
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There are a couple of possible reasons.
  1. The first is that you are reading or operating the meter incorrectly .Let's assume that's not the case. However I have been trapped by this in the past where the probes were plugged into the incorrect sockets for the range I selected. Confusingly, one of my meters (at least) will still give readings (wrong ones) in this state.
  2. The next possibility is that it is a problem with burden voltage. If the circuit under test operates at very low voltages, a combination of the current being measured and the resistance across the meter can change the circuit operating conditions. For a simple multimeter, this means the current read on the lower range (which uses a higher resistance shunt) will measure lower current.
  3. Another option is a flat battery. A very cheap multimeter I have starts to read very inaccurately when the battery gets flat. Unfortunately the manufacturer decided to omit a low battery indicator :-(
 
Last edited:

kellys_eye

Jun 25, 2010
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My suggestion would be that it's a cheap meter.

Sadly you can be encouraged to purchase cheap (but useless) meters when there are actually some very good 'cheap' multimeters out there - like the AN8008 for example has had 'rave' reviews for its functionality and practicality.
 
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