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multi-meter questions

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Tom/Idaho

02-19-2008 09:45:04

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I have a CDI unit from a Kawasaki 220 that I belive may be bad. The testing directions say to test for resistance between the terminals by setting the meter to its R x 1,000 scale. The values should run betweem 0.45-1.8 or 29-116 (just a few of the values listed). My digital meter does not have a R x 1,000 scale. Just has 2, 20, 200, 2000 and 20M. Will the readings be different if I use a different scale? Or when the testing directions say use a certain scale do they mean use that exact scale?
Thanks, Tom/Idaho

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dave guest

02-19-2008 18:07:18

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Re: multi-meter questions in reply to Tom/Idaho, 02-19-2008 09:45:04

You mean open is infinity. Ground is zero.

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Bob Huntress

02-19-2008 19:37:40

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Re: multi-meter questions in reply to dave guest, 02-19-2008 18:07:18

yes

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dave guest

02-19-2008 18:06:42

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Re: multi-meter questions in reply to Tom/Idaho, 02-19-2008 09:45:04

You mean open is infinity. Ground is zero.

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Bob Huntress

02-19-2008 17:48:54

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Re: multi-meter questions in reply to Tom/Idaho, 02-19-2008 09:45:04

To answer your question, imagine that your CDI is going to test satisfactory. Which scale would have that reading as close to the scale? If you use the 20M scale, a reading of 0.45 will hardly move the needle on the needle type. You can always change the scale and take another reading, if you think that you have either too small or too large a scale.

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Bob Huntress

02-19-2008 17:16:59

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Re: multi-meter questions in reply to Tom/Idaho, 02-19-2008 09:45:04

Did they tell you what to look for? This is far more usefull. If you have an open, you will read zero. If there is a ground etc, you will read infinity, in almost all cases. When I check the three terminals on a hermetic compressor, I use the difference between the different readings to determine which prong is which, but most of the time, you have zero, infinity or anything else. Anything else, usually being a good resistance reading. Now a CDI does have tighter resistance than that, but remember, if your readings are anywhere near close, they are probably good. If you don't get either a zero or infinity, and you aren't comfortable with your multimeter, have someone who is more experienced second check, because the odds that you actually have an out of spec resistance reading that is neither zero or infinity is lower than average.

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tech4

02-19-2008 11:10:59

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Re: multi-meter questions in reply to Tom/Idaho, 02-19-2008 09:45:04

There are several variables here. There is usually a difference in the measuring voltage for ohms between an analog and digital meter. If there are solid state devices across the measurements then the readings may vary even when correct. But if it is pure resistance then either meter will read the same. Does your digital meter have a K after any of the 20,200 or 2000 settings like the M on the 20M scale?

Readings such as 0.45 on the RX1000 scale would be 450 ohms or 1.8 would be 1800 ohms. If 2000 on your digital meter is 2000 ohms then 450 or 1800 would read right. Just multiply the readings they list by 1000 and read on the scale in range. The readings like 29-116 on the RX1000 scale would equal 29,000 or 29K and 116 would equal 116,000 or 116K If there is a K after any of your meter settings then 20K would equal 20,000 ohms. If just 20 then that would be 20 ohms full range. What is the model of your digital meter?

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Jerry/MT

02-19-2008 09:58:44

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Re: multi-meter questions in reply to Tom/Idaho, 02-19-2008 09:45:04

Use the 20 or the 200 scale for those range of values. No, the readings won"t be different. 100 ohms is a 100 ohms. The needle will appear in a different position on the face of the meter (if you have an analog meter) than if you use the 2000 scale (for example)instead the 200 scale but it should still read the correct value.
You can try changing the scales to check this.

If you have a digital meter, it shouldn"t matter.

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Gerald J.

02-19-2008 11:57:54

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Re: multi-meter questions in reply to Jerry/MT, 02-19-2008 09:58:44

Depends on the circuit and the multimeter or digital multimeter. Likely they prefer the X1000 range to limit the current from the analog ohmmeter. There may be diode junctions in the path and the X1000 range usually has higher test voltage too. Each junction has 0.6 volt drop and if forward biased with an ohmmeter to only 0.5 volt it will test open.

Some digital multimeters while check diodes on about half their ranges, and when show the resistance through a diode, the "resistance" reading is more one of the forward drop of the diode than the circuit resistance and will tend to show about the same numbers on different scales because the forward drop isn't much dependent on current while the digital ohmmeter applies a current and measures the resulting voltage drop to read ohms.

To read 2500 ohms on the digital meter you will have to be on the 20,000 scale else 2500 ohms will be offscale on any lower resistance range.

Gerald J.

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MarkB_MI

02-19-2008 18:55:02

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Re: multi-meter questions in reply to Gerald J., 02-19-2008 11:57:54

Yep.

A lot of the older DMM's wouldn't check diodes on any range. Not enough voltage to forward bias a diode.

Most folks don't realize that the "diode check/continuity" scale on most DMMs (Flukes in particular) doesn't measure resistance at all. It usually measures voltage drop. Which means that the "continuity check" is usually a poor check of continuity!

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