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Measuring resistance with multimeter

Posted by littleblu87 (My Page) on
Tue, Apr 14, 09 at 6:29

Please excuse my ignorance regarding multimeters and electronics. I'm in the process of trying to learn about all that stuff.

I need to test a 1M ohm resistor to confirm that it's working.

Apparently the multimeters I'm considering buying are manual range. So to test a resistor I would have to turn the dial on the multimeter to one of these settings: 200, 2000, 20k, 200k. But some multimeters have 2000k and some have 20M. Does that matter at all for testing a 1M ohm resistor? If so, which is better? I don't think I need an auto-ranging multimeter. That would probably be a little over the top for my needs right now.

Does it matter whether the input impedance of the multimeter is 10M ohm or >1M ohm? Or does that not have anything to do with testing resistors? That has to do with voltage, right? This stuff is so confusing.

Follow-Up Postings:

RE: Measuring resistance with multimeter

you would need a range that is higher than what your testing...

2000k = 2M

also, you would probably need to remove the resistor from the circuit,
so that you're not reading any other components in the circuit.

RE: Measuring resistance with multimeter

I agree with Regis, but I would add that sure, you can test the resistor out of the circuit, and if it looks burned then it's already out of spec (resistance will keep climbing when it overheats) but would point out that a replacement resistor will cost you less than ten cents if you can get one, say at an electronics specialty store. I always spend the extra two cents or so, and get metal film as they last longer and stay more consistent over their life. Carbon film is ok for most things though.

What makes you think the resistor is at fault? Unless the circuit is very badly designed, the resistor should not overheat or fail unless there's something else wrong in the circuit or the resistor's physically damaged.

When replacing the resistor, make sure you use fine nosed pliers to hold the resistor wire right next to the body before you bend the wire - if you just bend the wire, you risk damaging where it attaches.

RE: Measuring resistance with multimeter

You can get a digital meter from Harbor Freight for $2.99, battery included!!! You can get one step up for $10.00. I bought one of each just to see how they perform and haven't seen any difference between the two other than color and price. I have several meters which run into the hundreds of dollars and have found these "cheapies" to do well for general testing, such as what you want to do.

RE: Measuring resistance with multimeter

If the dial shows 200K max, you can't measure a 1M Ohm, obviously.
A 2000K or 2M setting will measure it just perfectly.
A 20M setting will measure it, but much less precize than when you have a 2M range. But just to see if it works or not, even that would be OK.

RE: Measuring resistance with multimeter

A meter with 2M as totsl resistence range will not measure a resistence greater than 2 megohms and you intend using a DVOM for general handy man testing this is adequate. If you plan to work on electronic circuits spend 10 bucks and get one with 20M range

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