VOM -- How to use

I have an active post about an attic fan, but noted that I don't really know HOW to operate my "Portable 27-Range Multitester," an analog VOM from about 1980-82.
It has an instruction manual that is about as clear as mud. I have also read the appropriate pages in my "Readers Digest Fix-it Yourself" book and my Time-Life "Complete Fix-it Yourself Manual"
What I don't understand is I have four dial settings areas basically 1. ACV 2. DCV 3. DCUA (the U is some south of wierd symbol, looks like a U..sorta) 4. A Greek symbol, I think it's Omega (sorta of a squashed upside down U).
Then there are four holes for the banana plugs. 1. COM, 2. V-(Omega?)- A 3. AC 1KV 4. DC 1KV
And of course the dial sections are a gobbly gook of RX1 or 1KV or . 25, you get the picture.
All I want to know most of the time is if there is current flowing and if there is, how much?
How do I measure that? Any good webpages? I think I looked last March when I was doing some wiring work in the car, but I never found anything. I ended up just using my continuity tester....even I can figure out "when the bulb lights, there is juice!"
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The upside down U - Omega is a continuity tester. DO NOT have it in this position if there is any current involved, it will fry the meter. This setting demands a battery inside your tester. When you touch the two leads together you should read wide open.
I assume you want to measure AC current in the house. Set it on ACV. Set the scale multiplier to be able to read what you think should be in the circuit. If you are measuring 110 volts, make sure you are on a scale that has 110 about in the middle.
DCV same game, direct current - e.g., automotive
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While we're nitpicking your post, "wide open" is not clear.
When he touches the leads togeher while the meter is in position 4, ohms, the needle should go all the way to the right.
BTW, OP there is a knob or the edge of a knob that you can use to move the needle so that it sits on the right-most line of the scale, Zero on the ohms scale (marked with an omega at one or both ends) to calibrate the ohm scale. This needs to be done because unlike the other measurements, this will vary as your battery gets weaker.
But if you are only checking for continuity, the meter doesn't have to be that accurate.
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On Sat, 09 Jun 2007 11:39:06 -0700, snipped-for-privacy@mailcity.com wrote:

Read to the end before using the meter. It seems complicated, but after a few times it will look more and more simple.

AC is for alternating current, such as house current.
DC is for direct current, such as what comes from batteries and almost all of the voltages in a radio or tv. (The places electrically close to the wall cord of a radio or tv are going to be AC, but it gets changed to DC soon after.)
The V in 1 and 2 stands for voltage**. That's what you are interested in in the other thread. Is there any voltage available? Use the ACV If the needle moves at all, you probably have the right voltage, but later, I'll probably get to how to measure how much voltage there is.
In switch location 3, the U is probably a Greek mu. It looks like a lower case n upside down. Like a u but with the tail on the bottom left and not the bottom right. In text, where people don't have Greek fonts, they will use a plain old English u. Mu is short for micro. The A is for amp, a measure of the amount of current** So position 3 is for measure DC micro-amps. In practice, you won't need to measure amps much, only volts and ohms. Details of how to measure all of them further down.
Switch location 4 is, you're right, an omega. Which is an O in Greek, and was chosen, not by Greek speakers, to represent Ohms. (Ohm was an early scientist who worked on electricity, as were Volta, Ampere, Faraday, and Henry.) Ohms are a measure of resistance to electric flow. NEVER measure using the ohms scale before you have measured with the voltage scale. You want that there is NO voltage when trying to measure ohms. The thing is unplugged, for example. At best, you won't get the right answer if there even a small voltage present, and at worst it's easy to burn out the meter, or one resistor in it. Then, even if you can fix the meter, and maybe no one can, you'll need another meter to fix it with!
Meters in 1980 might have had some overvoltage protection, but you want to get in the right habits and not rely on that. For one thing, I'm sure it's not always enough, even when it's there.

3 is only for AC voltages over 1000. You'll probably never need this.
4 is only for DC voltages over 1000. Outside of a tv, you'll probably never have this.
3 and 4 are holes for the red wire. The black wire always stays in 1, the Com hole.
So that means you'll use 1 and 2 for everything else. Put the black wire in 1 and the red wire in 2. Sometimes I put an alligator clip on the black wire, instead of the probe. Then I need one fewer hand to use the meter. (Or you can buy a bag of 10 wires with alligator clips on each end, at Radio Shack. 5 colors, two of each, costs 2, 3 or 4 dollars. Many many uses, including attaching the negative probe of a meter to something, such as a known ground.

What you probably want to do is measure if there is voltage present. It's too inconvenient to measure directly for current. In fact, you'll notice that you don't even have an ACA scale. Most meters don't, and that is still true today. :)
If there is voltage, you can turn off the voltage at the breaker, or disconnect those wires you connected, the black and white, and measure the resistance of the fan/thermostat combination. If the needle moves, with the first knob in posistion 4, ohms, and the other know in the Rx100 or Rx1000 setting or any setting, you have "continuity", there is a continuous path for the electricity to go through.
If the needle doesn't move at all, you want to narrow the problem down, by checking the thermostat first and then the motor, to see which one is "open", a break in the path of electricity.

**There are enormous similarities between electricy in wires and water in pipes. When looked at this way, Voltage is equivalent to water pressure; Amperage (current) is equivalent to gallons per minute; and Ohms or resistance is eqivalent to the resistance to water flow of the pipes. That is, smaller diameter pipes have more resistance than bigger diameter pipes
How much is the meter showing there is.
The full scale reading will have a number, like 100 maybe, so if the needle is deflected full scale, and the X1, X100 switch is on X1, you'll be showing 100 units of whatever you are measuring. 100 volts, 100 ohms, 100 microamps
Got to stop now. Continued later if possible. There is enough here for you to get started.
If not, ask questions. :)
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Are you sure about this? I seriously doubt that an old meter like this is designed to measure multiple thousands of volts. This is probably a 1000 volt max range.
Bob
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Ranges: 27 DC Voltage 0-0.25-1-2.5-10-25-100-250-1000V
AC Voltage: 0-10-25-100-250-1000V
DC Current: 0-50-500U A, 5mA-50mA-500mA
Resistance 0-6K Omega (midscale 30 Omega) 0-60K Omega (midscale 300 Omega) 0-600K Omega (midscale 3K Omega) Decibels (HUH< I thought that was sound) -22dB ~ +22dB ~ + 62dB in 5
Sensitivity 20,000 ohms/volts DC 10,000 homs/volt AC
Fuse 0.5A, 250 V 32mm
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On Sat, 09 Jun 2007 13:27:57 -0700, snipped-for-privacy@mailcity.com wrote:

This almost certainly means that there will be at the far end of the scale, opposite from where the needle normally rests, the numbers 25 and 10.
25 will mean different things for different settings of that switch. It will mean either .25, 2.5, 25, or 250.
There will also be other numbers midrange, the same color and the same positioning relative to the other numbers as the 25, that help you to read lower values, probably 5, 10, 15, and 20.
10 will also mean different things for different settings of that switch, either 1, 10, or 100, and if the 1000 volt jack is used 1000.
There will aslo be other numbers midrange, the same color as the 10, maybe 2, 4, 6, and 8. The positioning helps you keep track which set of numbers you want to look at, based on the swtich setting you chose.

Same thing as above. IIRC, on some meters, 25 for AC doesn't show up in the same place as 25 for DC, for example, but the color coding should make it clear which is which. Or there will be ~ to represent AC current on the AC scale. AC scale number are usually red for some reason, iirc.

Each of these is ten times more than the one to the left. Including that 5mA is 10 times 5uA. Stop using a capital U and use a lower case u instead. If your manual uses an upper case U, it's wrong. (probably printed in Japan, and no one really skilled wants the manual writing job.) A capital mu in Greek looks like a capital M in English. Only a lower case mu looks pretty much like a u, a lower case u. (Look in the dictionary under "alphabet" for important alphabets.

This is usually measured on a different scale, with an omega at one or both ends, the scale is usually black and closer to the pivot of the needle than the others. It will not have a 6 at either end because the left end is infinity and the right end is zero. There is a knob or the edge of a knob with which to "zero the meter", by touching the leads together and turning the knob until the needle is above the zero mark.

It's also ratios, though I have never used and don't know how to use the decibel scale.
For 25 dollars, you got a good meter. Not the best of course but not junk either. Probably has a mirror? Do you know how to use that?

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wrote:

Oops. 5mA is 10 times 500 uA.

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wrote:

You're right. I was wrong. For voltage up to 1000.
But he'll still never need these scales because 110 and 220 are easier to read on the regular scale with the range set right.

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I am so close to almost "clicking" (ie, understanding) this it is painful.....THANKS MUCH. Your explaination is great
However, remember I am a babbling idiot here....so when you say:

How exactly do I do this...that is measure the resistance of the fan thermostat combo.....do I touch the meter probe to the disconnected "house" black wire and then to the thermo connection? Or is it some combo of black house wire, black fan wire, white house wire....well you get the idea, I am sure...I hope.
And again, thanks. you have already put me way ahead of the instruction book....

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On Sat, 09 Jun 2007 13:20:17 -0700, snipped-for-privacy@mailcity.com wrote:

(Read the whole thing before going to test)
That's pretty much the second step.
The first step was: One probe to the black wire that was disconnected from the house (the wire that goes to the thermostat) AND the other probe to the white wire from the fan motor. (whether connected to the house white wire or not.)
This is an easier test to make, and if the needle moves, it means that BOTH the fan and stat are conducting electricity.
But only if the needle moves are you done with this part.
More likely is that the needle won't move and then you have to narrow it down to the motor or the stat.
Then you want to do pretty much what you say above "..do I touch the meter probe to the disconnected "house" black wire and then to the thermo connection?" Except not if you mean by "house" black wire, the wire from the house. You want to use the wire from the thermostat. And you have to find the thermo connection to the motor.
BUT, NONE OF THIS WILL WORK WHILE THE TEMP IS COLDER THAN THE MINIMUM STAT SETTING. If it is 55, the stat is open, the contacts are not touching, the current can't go through. Even with the stat set to 60. No one wants his attic fan going on when it is 55 inside the attic, and even if it is warmer than that, since attics are often warmer than the outside..... Well maybe it is over 60 in the attic, so take another thermometer up there with you and see what that says. Remember taht the stat can be off a few degrees and the thermometer could be off a degree or two in the other direction.
This is why I suggested bypassing the stat, to see that the motor runs. In some cases another method would be to point a heater at a thermostat.
You might also maybe be able to peak into the thermostat and see the contacts, and see that they get closer together when you turn the stat towards 60 from higher.
BTW, not only do I have a swtich to turn the fan off in the winter, but I have one to turn it on even when it would other wise be off, recommened for people who get too much humidity in their attics from using the shower a lot with an indadueate batheroom fan.
That swithc bypasses the thermostat, so it must be pretty easy in my model to bypass the thermostat and maybe yours.

BTW, in your post in answer to BobF, you write things like midsacle 30 Omega. The omega is read as "ohms", 0-6K ohms. Omega is the Greek letter and it is the symbol for ohms, or ohm if there is one or less.
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On Sat, 09 Jun 2007 13:20:17 -0700, snipped-for-privacy@mailcity.com wrote:

Let's step back a few feet and look at the general issue.
There are two parts to an electric circuit.
The part that provides the power and the part that uses the power.
To test the first, you need a voltmeter, to see if there are any volts (a measure of electric potential, EMF, but in the loose sense of the word, a sign of power. (Not power measured in watts, which is a more formal thing.))
To test the second, you need an ohmmeter to see if it's going to be possible for any of that electricity to get through the second part and do some work.
(You could say there is a third part, the wires between the two, but in this example, I'm putting all the wires in either the first part or the second part, based on wherever one splits the thing into two parts.)
A simple example: A flashlight that doesn't light. In only opens at the front. What most people do first is open the flashlight, slide out the batteries and see how much voltage they have. (That's like checking if there is AC voltage at the black and white wires.)
If the batteries are good, what most people do (at least me) is put the two probes of an ohmmeter on the front part of the flashlight that has the lightbulb in it.
Too tired to finish. Let me know if this is helpful and if so, I'll try to finish it later.
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wrote:

FTR I think I'm wrong here, that maybe one can get the right measure of ohms across a resistance, even though it has a small voltage present, but you shouldn't do it anyhow. WRT houses and cars there is no need. And I don't think anyone does it. Measurements of voltage are adquate.
The only likely voltage in a house is 110 or higher. That's not a small voltage and will burn out a lot of meters. Small would be only a little greater than the battery in the meter.
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On Sat, 9 Jun 2007 15:49:09 -0400, "Charles"

Yes, you're right. I said OVER but should have said UP TO.
But he still won't have any use for jacks 3 and 4 most likely because all the voltages he will find will be easier to read with the red wire in jack 2, and the right scale chosen.
Maybe I'm wrong. Does anyone actually use the 1000 volt AC scale for house current?

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snipped-for-privacy@mailcity.com wrote in

ACV= AC voltage,what comes out of your home electric outlets. DCV is DC voltage,,your car battery is DCV. (DC= direct curernt,meaing not alternating current[AC]. Voltage is measured across the source.(parallel)
DCuA is DC current,uA= microamps(u= micro,small m= milli). your meter should have several current ranges,the meter has to be in SERIES with the current source.
Omega = OHMS, resistance measurement,or "continuity". DONT apply any voltage or current in this mode,you will damage your meter.

COM= common,volts,amps and ohms share this terminal,usually the negative side (black wire/lead) V-A is volts/amps,the RED or positive lead. AC 1KV is the 1000 volts range,high voltage,DC 1KV is for DC high volts. these are separate jacks for safety reasons,to remind you you are working on high voltage.

Rx1 is ohms scale reading times a multiplier of ONE. Rx10 would be the scale reading times TEN,Rx100 times 100,etc.

Yes,but the meter will tell you how much "juice". IOW,the voltage could be low,like a 12V car battery that only reads 10V.
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Finding the keyboard operational snipped-for-privacy@mailcity.com entered:

Try http://colomar.com/Shavano/vom.html and read the Testing AC Power section. Ignore the ohms (upsidedown squased U) and the amps settings. Voltage and power are 2 different things. For right now, ignore current (amps). IF you are still unclear on how to use your meter then doen't use it. You will be exposed to voltages that can kill you. Another suggestion is to go to Radio Shack and buy a cheap digital meter and read the instruction booklet. While you are there see if the salesclerk can show you how to useyour analog meter. Bob
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To make voltage testing in your house a lot easier just get a rubber pigtail socket and a rough service light bulb to screw into it. If the bulb lights, you have juice. If it doesn't light then the circuit is dead or you have a problem.

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snipped-for-privacy@mailcity.com wrote:

AC volts, DC volts, DCmicroAmps, and Ohms

COMmon, Voltage, AC upto 1000 volts, DC up to 1000 Volts

You can't.
VOM stands for Volt, Ohm, Milliammeter.
Current is measured in amps; your meter can measure - at best - some thousandths of an amp.
Buy a Kill-A-Watt box for ordinary household measurements. It'll measure volts, watts, Hertz, kilowatts, kilowatt hours, and other stuff. Here's one on Ebay:
http://cgi.ebay.com/Kill-A-Watt-LCD-Electricity-usage-monitor-meter-P4400_W0QQitemZ160124420359QQihZ006QQcategoryZ3188QQrdZ1QQcmdZViewItem
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HeyBub wrote:

You can get an inductive probe for measuring AC amps and it doesn't require breaking the circuit. You just snap the probe around one wire and use the milliamp current range on the VOM and read it as amps instead of milliamps.
Good ones are expensive though which is why you mostly only see pros having them.
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snipped-for-privacy@mailcity.com wrote:

You need to learn electrical fundamentals first, and meter usage second. Trying to teach you this via usenet is like trying to teach a dog to play piano.
Not trying to be insulting. You're just wasting time & wearing out your keyboard.
Try this instead:
http://cgi.ebay.com/BASIC-ELECTRICITY-AND-CIRCUIT-CONCEPTS-DC-CIRCUITS_W0QQitemZ280121594435QQihZ018QQcategoryZ378QQrdZ1QQcmdZViewItem
No idea if that URL will make it, so it's ebay auction #280121594435
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