anyone familiar with multimeters?


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Old 01-01-10, 08:47 PM
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anyone familiar with multimeters?

Hey guys. I bought an Ideal 61-360 multimeter from the Home Depot to work on my motorcycle with. I am having ignition troubles, and thought this would help with determining if I have a generator issue.

There are seven resistance settings. The first is labeled with a right arrow and a plus sign. The second says 200, the third says, 2k, the fourth 20k, the fifth 200k, the sixth 2m, and the seventh 20m. I have no idea what the right arrow and plus size mean, as the instructions don't mention it. When I touch the probes together, it displays a few numbers (for example: 0.700, 0.05, 0.001) and then it displays 0.00 with a minus sign occasionally flashing in front of it.

However, when I set it to 200, which is supposed to be the actual ohm reading, it displays some very high numbers (for example: 73, 12, 1.5, 0.9) and then it settles down at 0.5 and stays there. Does this mean my multimeter is innacurate? Shouldn't it be reading zero when I do this?

As far as the rest of the settings go, the go straight to zero with the exception of the next setting, the 2K or 1:1000 setting. It displays .002, then .001 in the matter of a second and then shows zero.

Is all of this normal? I am surprised with my 200 (or 1:1) setting that it registers 0.5.
 
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Old 01-02-10, 01:22 AM
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Welcome to the forums.

The arrow with a plus sign is actually the schematic circuit symbol for a diode. You can use the meter to test diodes with that setting. For example, the diode on an alternator.

The other numbers are the "range" of ohms that the meter wants to work with so it can be most accurate. If you're looking for continuity (checking wire connections), use the 200 ohm setting. The 0.5 ohm reading when you touch the two probes together is normal. The metal on the sides of the probes will never make a perfect connection, so there will always be some resistance indicated on the meter.

It's also normal for the meter to display erratic numbers when you first touch the probes to the test points. It takes a second or two for the meter to lock in and settle down to a proper reading.

2k = 2,000 ohms. 20k = 20,000. 2M is 2 million ohms.

When you touch the probes using any of these settings, the meter isn't accurate at reading low resistances like half an ohm. It settles on zero. That's also normal.
 
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Old 01-02-10, 06:39 AM
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Just another "throw in", when working on your cycle voltages, be sure to use DC, rather than AC settings. You knew that, I'm sure. Doing electrical work all day, I find myself automatically setting mine to AC, and trying to work on my truck.....duh.
 
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Old 01-02-10, 08:54 AM
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Originally Posted by Rick Johnston View Post
Welcome to the forums.

The arrow with a plus sign is actually the schematic circuit symbol for a diode. You can use the meter to test diodes with that setting. For example, the diode on an alternator.

The other numbers are the "range" of ohms that the meter wants to work with so it can be most accurate. If you're looking for continuity (checking wire connections), use the 200 ohm setting. The 0.5 ohm reading when you touch the two probes together is normal. The metal on the sides of the probes will never make a perfect connection, so there will always be some resistance indicated on the meter.

It's also normal for the meter to display erratic numbers when you first touch the probes to the test points. It takes a second or two for the meter to lock in and settle down to a proper reading.

2k = 2,000 ohms. 20k = 20,000. 2M is 2 million ohms.

When you touch the probes using any of these settings, the meter isn't accurate at reading low resistances like half an ohm. It settles on zero. That's also normal.
Thanks for the replies Rick and Chandler!

Rick, I see what you are saying about it reading .5 on the 1:1 range. The connection between the leads isn't perfect, therefore it won't read zero. And on the higher ranges, it can't read that accurately at such a low ohm, so it displays zero.

With that said, I am supposed to be seeing between 0.05 and to 0.2 on one of my generator coils, according to my service manual. Do you think my multimeter can read that accurately? I am getting a reading of 0.6-0.8. It changes every few seconds. Obviously this is out of spec per the manual. Can I assume that the .6-.8 reading are accurate? Is there a way I can calibrate it to make sure?

Someone told me to go buy some 1ohm resistors and test it that way.
 
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Old 01-02-10, 09:06 AM
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A diode is an electronic component which only allows electricity to flow one direction.

Diodes are commonly used in cars to keep electricity from flowing backwards into something it should not.

For example the same light bulb on a car might be used for the turn signal and the hazard flasher. And if you turned on the hazard and turn signal at the same time with the ignition off, the electricity would flow backwards and power everything else in the car! So they use a diode in the wiring to prevent this from happening.

In some older cars, you can turn on the hazard and turn signal, then the radio will flash on/off! (no diodes installed yet.)

Digital multimeters use very little electricity to test circuits. However diodes require 7/10 of a volt to activate them and test them. Older multimeters could not test diodes because they were not sending enough electricity through the test leads to "activate" diodes. So with newer multimeters, they came out with a special test setting for testing diodes or wiring circuits which have diodes in them.

So if testing a car wire and that particular wire has a diode buried in it along the way, if you tested using the regular ohms settings, it would read "open". But with the diode setting, it would read as a good circuit. And you must also have the test leads connected so the electricity from the meter is going the right direction when testing diodes. Remember electricity flows only one direction with a diode.

In the following car wiring diagram, two diodes are used for the neutral switch. These diodes keep the "positive" electricity from one side from going to the other side. But to test from the neutral switch to the neutral light or to the clutch switch, you would need to set the multimeter to the diode setting and have the test leads going the right polarity...
http://www.wiringdiagrams21.com/wp-c...ng-diagram.png
 
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Old 01-02-10, 10:43 AM
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As far as measuring .05 to .2, if those are ohms, no the meter you have will not accurately measure at that low a reading, however, for trouble shooting, you are more often looking for continuity or open. If you add back in the contact resistance you saw with the leads touching, you are actually fairly close. But for trouble shooting with inexpensive meters, it is like horseshoes, close counts.

Bud
 
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Old 01-02-10, 10:57 AM
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Originally Posted by tripleup05 View Post
I am supposed to be seeing between 0.05 and to 0.2 on one of my generator coils, according to my service manual. Do you think my multimeter can read that accurately? I am getting a reading of 0.6-0.8. It changes every few seconds. Obviously this is out of spec per the manual. Can I assume that the .6-.8 reading are accurate? Is there a way I can calibrate it to make sure?
Since you know that the meter will read .5 ohms when you touch the probes together, subtract that from the readings when you measure the coil. The coil resistance reading is actually .1 to .3 which is about as accurate as you can get. I'll bet the changes are due to the pressure you're using when you apply the probes.

Also, are you removing the wiring to the coil when you test it? Many components have to be measured with nothing else connected to them.

Someone told me to go buy some 1ohm resistors and test it that way.
Problem is, one of the specs of a resistor is "tolerance", which means it can stray from its stated value in either direction. A 1-ohm resistor with a 20% tolerance could read anywhere from .8 to 1.2 ohms and you wouldn't know whether the error was due to the meter or to the tolerance. Because the meter is new -- and made by a reputable company -- it's probably accurate.

That said, have you checked out the DIY Motorcycles forum?
 
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Old 01-02-10, 03:31 PM
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Originally Posted by Rick Johnston View Post
Since you know that the meter will read .5 ohms when you touch the probes together, subtract that from the readings when you measure the coil. The coil resistance reading is actually .1 to .3 which is about as accurate as you can get. I'll bet the changes are due to the pressure you're using when you apply the probes.

Also, are you removing the wiring to the coil when you test it? Many components have to be measured with nothing else connected to them.


Problem is, one of the specs of a resistor is "tolerance", which means it can stray from its stated value in either direction. A 1-ohm resistor with a 20% tolerance could read anywhere from .8 to 1.2 ohms and you wouldn't know whether the error was due to the meter or to the tolerance. Because the meter is new -- and made by a reputable company -- it's probably accurate.

That said, have you checked out the DIY Motorcycles forum?

Thanks, Rick. So perhaps I am in spec, or atleast close, afterall.

When you asked "Also, are you removing the wiring to the coil when you test it," are you asking if I have removed the wiring from the coil, or if I have removed it from what the wiring connects the coil to? (which is a CDI controller) I have removeed it from the CDI box, per the manual, but I don't think I can remove it from the coil as it is soldered.

I will check out the MC forum! Thanks!
 
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Old 01-02-10, 03:50 PM
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Having a correct reading with a multimeter does not necessarily mean it is good, only that it isn't open. It may break down under higher voltage then used to read ohms in a multimeter.
 
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Old 01-03-10, 04:42 AM
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I was referring to the wiring that connects to the coil, not the wiring inside the coil.
 
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Old 01-03-10, 01:23 PM
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You cannot measure resistance under a few ohms with any accuracy with a simple multimeter. The resistance of the test leads, and the varying resistance of the contact point make it too erratic. A four lead meter is used for such measurements.
 
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Old 01-04-10, 05:04 AM
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I wouldn't count on it for critical measurements, but his readings are "close enough" to tell him his coil is within spec.
 
 

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