Measuring DC amps with a digital multimeter

[krishunt]

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]

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]

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]

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*)]

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 :-(

 

[kellys_eye]

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.