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Old 23rd April 2007, 02:50 PM   #1
jarthel is offline jarthel  Australia
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Join Date: Jan 2002
Location: somewhere in Australia
Default measuring current load

I know that VOM these days can measure current.

BUT can i use this alternative method to measure current?

for example:

I need to know the current load of a circuit. So I place a 10ohm 50W resistor between the positive lead of the power supply and the circuit. I then measure the voltage drop across the resistor and use ohm's law to determine current.

OR maybe using the VOM's current reading feature still more accurate?

thank you for the help
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Old 23rd April 2007, 10:33 PM   #2
AndrewT is offline AndrewT  Scotland
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Join Date: Jul 2004
Location: Scottish Borders
Hi,
the voltage measuring scales in most multi-meters are more accurate than the resistance and current scales.

If your equipment can tolerate the slight voltage drop from an in-line resistor then voltage loss across the resistor is a good way to measure current. (it's what happens inside a multi-meter).

The resistance you can use can be quite low value and usually does not need to be high wattage. A 1r0 600mW can pass 770mA.
If this were fitted inside a mains fuse, one can with care measure upto 70W on mains equipment. The voltage reading at full current would be just 770mVac so the 2000mVac scale would be appropriate.
BUT TAKE REAL CARE THAT THERE ARE NO DISTRACTIONS, kids/animals/wife/husband around.
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regards Andrew T.
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