How to measure resistance?


I am trying to install a SunTouch spot warming mat. To check for damage you need to test the resistance of the wires using a digital ohm meter. Trouble is I have no idea what to set the meter at. If the Reistance Range of the mat is 70-86 what setting would I use on the meter? The meter is a Sperry DM-350A if that matters.
Thanks in advance.
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200 OHM scale.
Al
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Setting it to 200 on the OHM section always says 1__. no matter which wire combination I touch the leads with.
Here's a pic of the meter. http://www.awsperry.com/sperry/catalog?item=dm-300
I inserted the red lead into the V terminal on the right. Not sure if that's right or not, the manual is not very clear.
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It's not.

I agree that the manual could be better... but the markings on the front of the meter are VERY clear. To measure resistance, you plug one lead into the jack marked with the ohm symbol (Greek letter omega, the second jack from the left), and the other lead into the jack marked COM (common).
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Doug Miller (alphageek at milmac dot com)
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Doug Miller, 10/30/2006,8:26:35 PM, wrote:

And after you get the leads straight and make your readings ensure there is not a diode in line. Reverse the two terminals where you are connecting to and check your resistance again.
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Mike E. Fullerton wrote:

The leads plug into the "common" and "ohms (omega symbol) meter jack holes.
Sounds like you've got a wide open mat.
Tell us, if you touch the two meter leads to each other, do you get a reading of (or near) zero? If you do, the meter and leads are OK and you need a new mat.
Jeff
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Jeffry Wisnia
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On Mon, 30 Oct 2006 20:27:38 -0500, Jeff Wisnia

Touching the two leads together I get a reading of 00.2 sometimes 00.1. Not sure if this is considered near zero. When I touch the leads to the White/Black wires I get oscillating values between 78 and 80 which is withing the range of 70-86. White/Green and Black/Green wires give 1__. Hopefully that means "infinite" ohms (no continuity) and that would mean my mat is fine. Switching the leads in the terminals gives the same readings.
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On Tue, 31 Oct 2006 18:37:44 GMT, Mike E. Fullerton
White/Green and Black/Green wires

That sort of reading generally means "Over Range". If you're using the 200 Ohm range it could mean anything from just over 200 to no continuity. You could try the higher ranges to be sure.
Greg Guarino
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That's correct. Use the center terminal for the other lead (the COM). Then connect the two probes together, switch the dial to resistance and the 200 setting, and the meter should read something near zero. (If it doesn't read something like zero, perhaps there's a problem -- perhaps with one of the test leads).
From there, you're all set to measure your mat, or whatever it is.

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I doubt it very much -- what do you suppose the jack labelled with the ohm symbol is for?
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Doug Miller (alphageek at milmac dot com)
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snipped-for-privacy@milmac.com (Doug Miller) wrote in wrote:

he didn't look at the pix... the enlarged .jpg.
some DMMs use the V jack for ohms,this model is not one of those.
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Jim Yanik
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Oops, my mistake. I was looking at the wrong meter.
Use the two center terminals.
Mike E. Fullerton wrote:

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Yu need to have the red lead in the "ohms" jack,the one with the Omega symbol,between "A" jack and COM jack. Then use the 200 ohm range.
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Jim Yanik
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uNLESS I"m looking at the wrong picture, the A jack is for the 10 amp scale only. Everything else in this meter uses the middle jack for the black wire**, and the right jack for the red.
**This meter probably has autopolarity, that is, if you connect the wires backwards it gives the same reading***, but preceded by a negative sign.
***Unless there is a diode or other semiconductor between the two probes.
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you must be looking at the wrong pic,the DM-350A I looked at had 4 jacks; A for amps "omega" for ohms COM V for volts.
The TOP pix was a different model (DM-370)than what the OP cited.(DM-350A)
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Jim Yanik
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This is hard. If homework keeps getting harder, I'm going to have to drop out of school.
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Mike E. Fullerton wrote:

If you're just doing the typical installation, don't suspect damage and are performing the recommended periodic test during the installation the multimeter is fine. When I install radiant heating cable and suspect damage, I use a megohmmeter to test the insulation. The regular multimeter checks for breaks, but the megohmmeter is more sensitive and checks for leaks through the insulation.
Others have already addressed your original question. I answered one you didn't ask. ;)
R
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On Tue, 31 Oct 2006 00:03:29 GMT, Mike E. Fullerton

You don't need a digital meter. You can use almost any meter that measures resistance.

Al is right about 200 ohms for this, but in general, you can just try ranges at random, or in ascending or descending order until you find the right one. If you pick a range that is too low, the resistance will show probably as non-numeric on a digital meter, and the needle won't move on an analog meter.
If you pick a range that is too high, like 2 MegOhms, the digital meter will show Zero, and the needle will move all the way to the right on an analog meter.
Either way it will be unintelligible until you check what it says on other ranges.

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