Fun with multimeters

I’ve been going through A+ training as I have time. Whether I go through with getting the certification will depend on whether my bosses think having someone with an A+ lurking in the corner is useful–by contract I can’t do much more than swap a keyboard or mouse, but in the meantime I’m picking up some stuff I haven’t had to think about in a very long time.

One thing I picked up is the proper use of an ohmmeter or ohm meter.

Testing American Flyer track
Here I’m using a multimeter to test a piece of vintage American Flyer electric train track. I should get infinite resistance between the two rails, so this piece shows symptoms of having a short in it. On a good piece of track, my multimeter would read “1.”

Ohm meters measure resistance. Frequently, you’ll have a tool that does several things, so you flip your multimeter over to ohms or resistance to turn it into an ohm meter. Then, if you need to test a cable, put the red lead on one pin, and the black lead on the corresponding pin on the other side. If you get infinite or higher-than-expected resistance, then the cable is bad.

When you’re testing for continuity, you need to do so with the power off. Testing for continuity on a live system will cause the multimeter to malfunction at best, and at worse, blow a fuse. That’s a tricky bit you have to remember if you’re doing component-level testing on a board–something of a lost art these days. You might be testing voltage on a live system, then when you don’t see what you expect, you might want to test resistance. Be sure to remember to shut the system down when you switch from volts to ohms to avoid damaging your multimeter.

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