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Basic Electronics » Digital Multimeter will not show resistance!

September 13, 2011
by markwtaylor
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I bought the meter from NerdKits, and it will not measure resistors correctly. When I try to measure them, the number keeps bouncing around and will not stop, even after 5 seconds or so. And it's not like the bouncing is in the range - an example would be for a 1K resistor, it bounces between about 300 and 1.5K. I have tried different settings on the meter, but they all do the same.

Any ideas?

September 13, 2011
by Rick_S
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You're not touching the probes while measuring are you?

September 13, 2011
by markwtaylor
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No. I even tried using different wires instead of the probes in case they were at fault.

September 13, 2011
by mongo
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What happens when you touch the probes together?

September 14, 2011
by markwtaylor
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It zeros out, as it should.

September 14, 2011
by BobaMosfet
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First, you may only connect it one way to get the proper reading for what you're trying to do- you can't go changing settings. That alone could damage the meter, depending on what you're doing at the time (worst case), or give erroneous readings (best case). So be cautious.

For measuring a resistor, use Ohms setting, DC, and try it. The fact that the meter zeroes if you touch the probes together means it can tell the difference between resistance and not.

Normally if a meter value is bouncing around (and the meter is okay and properly set), it means you're not making good contact.

BM

September 14, 2011
by bretm
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I have to ask--are you trying to measure a resistor that is part of an active circuit?

September 14, 2011
by mongo
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OK, sounds like the meter is probably OK. If you are measuring a component that is connected to anything else, weird things can happen. If there is a capacitor in that circuit, the numbers will change. Usually by counting in one direction. Several other things in the circuit can also affect the readings. If you get different readings by switching leads, there is probably a semiconductor in the circuit.

Generally, I remove the component to measure so nothing else has any influence.

September 15, 2011
by markwtaylor
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bretm, No, these are resistors that are not in a circuit. In fact, they are new, and I have a lot of them to check. I am just organizing my parts and wanted to confirm the color-coding.

September 15, 2011
by mongo
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Could it possibly be just a cheap meter?

September 15, 2011
by BobaMosfet
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There is the possibility that it is in fact a bad meter. I know, that when I go to the store to get a new meter, I always take a known, good meter with me, and a known circuit (with an LED) to test.

I remember buying a meter a Sears, because my existing meter was 'near end of life'. Well, that didn't happen for a year. When I got the new meter out, I found its mode button was broken- and Sears no longer offered it- couldn't get any kind of repair. So I bought another meter at my local Sears, got it home, and it didn't work right. I borrowed a known, good meter to compare testing, and took the new meter back to exchange it. Next one was also bad.

I took the 2nd "new" meter back, along with the known meter, and a test circuit, and open two meters right there with the clerk and tested them both- they also were provably bad. The third one (the 4th overall) was good. I took it home.

So... it's possible it's just defective. See if NK can exchange it.

BM

September 16, 2011
by bretm
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Also check the battery in the meter.

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