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Old 06-07-2020, 01:51 PM   #1
JayChicago
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Default How to use and ohmmeter?

Ohmmeters show internal resistance if touching the two probes together. One of my multimeters shows .4 ohm. So when measuring resistance, do I need to compensate for that? If I measure the primary on a coil and see 1.4 ohm on my meter, is the actual resistance thru the coil 1.0 ohm? (.4 being the instrument's internal resistance)

(Sorry, can't correct the typo in the heading. System won't let me edit the heading)
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Old 06-07-2020, 01:53 PM   #2
JSeery
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Default Re: How to use and ohmmeter?

There should be an adjuster on the meter to zero it. I is normally a thumb wheel or something on the side of the meter.
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Old 06-07-2020, 01:53 PM   #3
V8COOPMAN
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Default Re: How to use and ohmmeter?

Most meters make provision to be able to "zero-out" that added resistance. JSeery's "meter" is obviously just a little faster than mine! DD
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Old 06-07-2020, 02:08 PM   #4
JayChicago
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Default Re: How to use and ohmmeter?

Neither of my inexpensive multimeters (but not Harbor Freight $8 meters) have that adjustment.
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Old 06-07-2020, 02:39 PM   #5
J Franklin
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Default Re: How to use and ohmmeter?

Maybe what it shows is the resistance of the leads, so just make the correction.
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Old 06-07-2020, 03:17 PM   #6
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Default Re: How to use and ohmmeter?

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Might need a new battery or clean battery connections
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Old 06-07-2020, 04:16 PM   #7
JayChicago
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Default Re: How to use and ohmmeter?

Quote:
Originally Posted by J Franklin View Post
Maybe what it shows is the resistance of the leads, so just make the correction.
Yes, that is what it is showing. The resistance of the leads, wires, plug-in connectors, etc. Yeah, I will just make a mental correction.

Tried a new measured-good battery. No change. Yes, good battery is important when using the ohmmeter function, because instrument sends an electrical signal in order to measure resistance. Both of mine have a low-battery icon that comes on if battery is low.
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Old 06-07-2020, 05:17 PM   #8
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Default Re: How to use and ohmmeter?

I have never seen a meter that didn't have an adjustment no mater how cheap. I don't think you are going to get any measurements that have any meaning going this way. You are basically just guessing, so why bother. Need to get a much better meter or borrow one. When you are working in the range of less than 2.0 ohms a 0.4 guess is a 1/4 to a 1/3 of the value!

Note: should have said analog meter, ohm zero does not apply to a lot of digital multi-meters. Also, it was noted that some newer analog meters do not have adjustment as well.

Last edited by JSeery; 06-08-2020 at 10:32 AM.
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Old 06-07-2020, 06:02 PM   #9
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Default Re: How to use and ohmmeter?

I have a fluke, a mid range older Craftsman, and a few cheaper units. The extra resistance is clearly in the leads when I can switch leads and see the difference in the same meter. I just touch them together and make adjustments to my readings. The Craftsman is the only meter with a zero button. I do have an old analog meter with a needle adjustment.
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Old 06-07-2020, 08:10 PM   #10
JSeery
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Default Re: How to use and ohmmeter?

Yes, I was referring to analog. Might take it to an auto parts place or shop and compare reading. I sure wouldn't make any decisions based on flaky readings.

Last edited by JSeery; 06-07-2020 at 08:18 PM.
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Old 06-07-2020, 09:57 PM   #11
J Franklin
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Default Re: How to use and ohmmeter?

Test it on a resistor. Look up the value codes online if needed.

Last edited by J Franklin; 06-07-2020 at 11:00 PM.
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Old 06-07-2020, 10:35 PM   #12
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Default Re: How to use and ohmmeter?

Most older VTVM's (analog) had an adj. with leads apart and adj. for leads together. Newer multi meters "may" have an adj. to zero with the leads together , not so on a digital, at least any I've seen.
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Old 06-07-2020, 11:43 PM   #13
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Default Re: How to use and ohmmeter?

Modern good multimeters are calibrated and donīt need adjustment...what is in the testleads are considered part of the circuit.
Even my new analog is fixed.
Older had the adjustment to compensate for the battery condition and was needed for this reason.
My bench multimeter uses 4wires and a special clip for low ohm readings to avoid this problem called kelvin 4-wire measurement.
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Old 06-07-2020, 11:45 PM   #14
JSeery
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Default Re: How to use and ohmmeter?

Quote:
Originally Posted by J Franklin View Post
Test it on a resistor. Look up the value codes online if needed.
There is a good idea, using a resistor to check the meter. A 1.5 ohm resistor would be idea.
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Old 06-08-2020, 12:29 AM   #15
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Default Re: How to use and ohmmeter?

Low ohm reading is not very accurate since resistance between testpoints even count in if not real clean...any oxide acts as insulator.
And go for a 1% metalfilm resistor if you want to keep a reference around...smallest power rating will do just fine.
Donīt grab a real old resistor out of the drawer....if carboncomposition they go high in value over the years.
Attached is a pic of the type of resistor to avoid for accuracy.
Attached Images
File Type: jpg cc1.jpg (3.3 KB, 4 views)
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Old 06-08-2020, 06:19 AM   #16
Terry,OH
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Default Re: How to use and ohmmeter?

Most of the digital meters do not have the ohm adjust. It is possible the meter is seeing resistance of the wire test leads. Solder joints where the wire connects to the terminals or probes on each end, plus touching one probe against another there is oxidized plating between the leads, maybe poor solder joints or broken strands of wire into the joints. The probes are pointed so the probe can get a better contact into what is being measured so if possible use the pointed end and not the side of the probe especially when measuring something of very low resistance and you need an accurate reading.
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Old 06-08-2020, 09:28 AM   #17
corvette8n
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Default Re: How to use and ohmmeter?

I had a cheap meter that had the adjustment inside, it was a tiny pot with a screw slot in it, had to take the back off to get to it.
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Old 06-08-2020, 09:45 AM   #18
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Default Re: How to use and ohmmeter?

Re the editing the title thing.
If you click on edit then go advanced, editing the title becomes available.
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Old 06-08-2020, 11:14 AM   #19
JayChicago
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Default Re: How to use and ohmmeter?

Mart: Thanks for that info.
And thanks everyone else, for the info/suggestions on the meter.
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