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I have a DMM and I have no clue how to use it, help!

post #1 of 8
8/21/04 at 5:25pm
Thread Starter 
I just got my DMM in the mail. At first I thought I was doing something wrong because I couldn't get it to read anything, so I opened it up and, lo and behold, the battery was starting to leak. So I popped in a spare 9V and it worked.

I think I understand the whole deal with choosing a range, but I am really confused by the three jacks. How do I know which lead should go into which jack?

Also, if somebody could give me a quick rundown of what all those ranges mean, just so I can be sure, that would be great.

As soon as I figure this thing out, I'll test my Cmoy's power supply section and keep building.

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post #2 of 8
8/21/04 at 5:36pm
The black lead should go to "Com". The red lead should go to "CV(ohm)ma".

Good luck on your cmoy.
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post #3 of 8
8/21/04 at 5:44pm
Thread Starter 
When do I use the 10ADC jack?

Does the black lead ever go anywhere except COM?
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post #4 of 8
8/21/04 at 5:51pm
Yes, the black lead stays in "Com".

I think the 10ADC is for measuring high current/high voltage for only a few seconds at a time.
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post #5 of 8
8/21/04 at 8:14pm
Quote:
When do I use the 10ADC jack?
You use it with the 10ADC setting on the meter. It's a fused 10A current metering setting. Current metering has to be fused because it works by measuring the voltage drop of the current across a very small resistor. (Fraction of an ohm.) Since R is tiny, Ohm's law (I=V/R) tells us that 'I' can be huge, for any V.

For all other measurements, you keep the red lead in the third jack.

You'll notice that you can do mA measurements with the red lead in the third jack. That may be unfused, or it might just have a small fuse only. The safest thing when measuring an unknown DC current is to put it in the 10A setting first, satisfy yourself that it's under the limit for the mA setting, and switch over to that if it's okay.

Quote:
Does the black lead ever go anywhere except COM?
To the extent that electrons care about the color of the wire, no. It's the "COMmon wire" -- always stays in the same place.
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post #6 of 8
8/21/04 at 10:47pm
You can't go wrong with ordering a pack of 10 fuses for you DMM as well. I've been using mine for many years yet i still get to blowing a fuse every so often. They are generally pretty cheap.

The DMM is also pretty indestructable, i was checking to see if the power was still on while working on a light socket, accidently had the red lead in 10A. Boom. Melted leads, dmm worked fine.

The ranges go from 0 to 200 for each measurement. Set it to mV and u can measure up to 0.2V, setting it to 2V moves the decimal point accross so you can measure higher. If you get a reading of 1 with no 0s on the screen it usually means you are measuring out of range, so switch up.

Going clockwise from off are the following measuremnets:
OFF
AC Voltage
DC Current
hFE (used for transistors which get put in the little ECBE box)
C is for temperature.
Diode measurement
Resistance
DC Voltage
OFF
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post #7 of 8
8/21/04 at 10:51pm
THat's the same meter I have. Mine came with a dead battery too. heh. At least it was only bulging, not actually leaking....
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post #8 of 8
8/22/04 at 1:07am
Quote:
They are generally pretty cheap.
Depends on the meter, I guess. There are two in my Fluke, and one's $4.50 and the other's $3. Encourages one to be careful...
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