How do I read ohms on a multimeter ? - Ford Mustang Forums : Corral.net Mustang Forum
 
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post #1 of 5 Old 06-11-2002, 01:49 PM Thread Starter
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Exclamation How do I read ohms on a multimeter ?

Hello, all-

This weekend I tried to test the resistance of my plug wires (original ones - 83,000 miles) using my brother's handy-dandy digital multimeter thingy. Then it occurred to me that I haven't the foggiest idea how to correctly read the thing.

On the meter, there is a dial where you can select each different function of the meter. On the "ohm" section there are five different settings:

2000
200
20k
200k
2000k

I tested the #5 plug wire - it is about 17" long.

With both the "2000" and "200" settings I got no reading. With the others:

20k = 5.56
200k = 5.5
2000k = 5

Sorry for the dumb question, but how do I interpret this? I don't know much about plug wires and ohmage and resistance, but I'm pretty sure that 7 year old original plug wires with 83,000 miles on 'em shouldn't have resistance that low. 5.56 ohms?

Thanks,

C


2010 CVPI

95GT AODE. Slow. Sold.
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post #2 of 5 Old 06-11-2002, 02:50 PM
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you want to use the lowest setting still in the range of ohms that you expect to read to get the most accurate answer.


i'm not sure what most plug wires are.. but 5 sounds really good!!

i'm going to check mine shortly, i have MSD-heli coil wires. how many ohms/ft are these rated at?

EDIT: MSD rates most of their wires at 40-50 ohms er foot. (3 foot wire, 120-150 ohms)


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post #3 of 5 Old 06-11-2002, 07:35 PM
 
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Re: How do I read ohmage on a multimeter?

Quote:
Originally posted by Neto95

This weekend I tried to test the resistance of my plug wires (original ones - 83,000 miles) using my brother's handy-dandy digital multimeter thingy. Then it occurred to me that I haven't the foggiest idea how to correctly read the thing.

With both the "2000" and "200" settings I got no reading. With the others:

20k = 5.56
200k = 5.5
2000k = 5

Sorry for the dumb question, but how do I interpret this? I don't know much about plug wires and ohmage and resistance, but I'm pretty sure that 7 year old original plug wires with 83,000 miles on 'em shouldn't have resistance that low. 5.56 ohms?
What you are measuring is called resistance and is measured in ohms. The K means 1000. If your range is 200K, the maximum resistance you can measure on that setting is 200,000 ohms. A reading of 5.5 would be 5.5 Kohms or 5,500 ohms. The lower the range, the better precision you will get. Notice that on the 20K range you saw 5560 ohms where on the 2000K, you saw 5000 ohms. Use the lowest range that gives you a number.
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post #4 of 5 Old 06-11-2002, 11:02 PM Thread Starter
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Lightbulb ah so...

mgranzow & Brian94Cobra-

thank you both for the prompt replies.

The best my brother and I could figure out was that each setting on the meter represented and "read" the same thing, but that the range was different. What we didn't know was where to put the decimal, and the whole "20-200-2000" thing threw us off. I figured that the "k" represented 1000, but I didn't know if 20k meant to multiply by 20 thousand, etc., and the fact that the values shown on the meter (5, 5.5, 5.56) were essentially the same threw a wrench into that theory as well.

But, Brian94Cobra, what you are telling me is that "20k" and "200k," etc. are merely representations of the particular range of resistance that particular setting on the multimeter displays as output, i.e. the 20k setting measures up to 20,000 ohms, while the 200k setting measures up to 200,000 ohms, etc.

What is actually displayed on the LED is essentially the same for all intents and purposes for this particular application; it's merely a matter of how it is "represented" or displayed. Therefore, if my #5 plug wire reads "5.56" on the 20k setting, that means that it is actually 5,560 ohms for 17", or 3925 ohms/foot. The same wire reads "5.5" on the 200k setting, equating to 3.88 ohms/foot. So, the moral of the story is to read the ohmage with the lowest setting possible to get the truest results..?

Interesting. Very interesting. It makes perfect sense! Now, if the multimeter was just a bit more intuitive a moron like me might be able to figure it out. Or maybe not.

Now, assuming that my horrible math is correct, 4000 ohms/foot isn't too terrible for 8 year-old-somewhat-neglected plug wires. Now when I switch over to MSDs or ACCEL I'll totally be able to shut down my brother's '99 35th anniversary GT (side note: for a 4.6, that thing make a hell of a lot of low-end power)

Love,

C

2010 CVPI

95GT AODE. Slow. Sold.
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post #5 of 5 Old 06-12-2002, 06:17 PM
 
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Re: ah so...

Quote:
Originally posted by Neto95

But, Brian94Cobra, what you are telling me is that "20k" and "200k," etc. are merely representations of the particular range of resistance that particular setting on the multimeter displays as output, i.e. the 20k setting measures up to 20,000 ohms, while the 200k setting measures up to 200,000 ohms, etc.

What is actually displayed on the LED is essentially the same for all intents and purposes for this particular application; it's merely a matter of how it is "represented" or displayed. Therefore, if my #5 plug wire reads "5.56" on the 20k setting, that means that it is actually 5,560 ohms for 17", or 3925 ohms/foot. The same wire reads "5.5" on the 200k setting, equating to 3.88 ohms/foot. So, the moral of the story is to read the ohmage with the lowest setting possible to get the truest results..?
You're on the right track. Use the lowest range you can get away with. When there's a K involved, you're looking at thousands of ohms. For your case, it's best to use the 20K range since what you're measuring is higher resistance than 2K, and lower than 20K.
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