# How much current does an ohmmeter use to test resistance?

Discussion in 'General Electronics Chat' started by geratheg, Mar 8, 2015.

1. ### geratheg Thread Starter Member

Jul 11, 2014
107
3
How much current does an ohmmeter typically send through a component to test its resistance? If it varies how much current does it use to measure as high as 2M ohms, 200k ohms, 20k ohms, 1k ohm? Is it in the nanoamp, microamp, or milliamp range?

2. ### MaxHeadRoom Expert

Jul 18, 2013
10,515
2,369
Depends on the meter.
Most electronic VOM's do not supply enough current to forward bias a diode, this is why there is normally a diode test position that registers the volt drop across the diode.
A moving coil meter, it depends on the Ma/deflection.
Max.

3. ### WBahn Moderator

Mar 31, 2012
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Most (not all) meters will have specs that will give you that information. You may have to search online for it.

4. ### geratheg Thread Starter Member

Jul 11, 2014
107
3
Okay I thought there would be a range. How about measuring resistance of a resistor? With a Fluke maybe?

5. ### crutschow Expert

Mar 14, 2008
13,000
3,229
My low cost Centech digital multimeter has a full-scale voltage on the resistance setting of 200mV (the open circuit maximum voltage may be some higher than that), on all ranges.
That's why they don't forward bias a diode. I think most low cost meters do the same (those with a most sensitive DC scale of 200mV).
Thus you divide 200mV by the resistance scale setting to get the (constant) current used to measure the resistance.
For example, at the 20kΩ scale setting, the current would be 200mV / 20kΩ = 10μA
Note that the current changes with the resistance scale setting on the meter.

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6. ### geratheg Thread Starter Member

Jul 11, 2014
107
3
I also have a Centech, but couldn't find the specs anywhere on the box and lost the user manual.

Thanks!

7. ### shortbus AAC Fanatic!

Sep 30, 2009
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Go to the Harbor Freight website and pull up the model number. They will have a PDF for that items manual there. They do that for all things they sell.