Multimeter Mini-Tutorial

[DrNomis_44]

I decided to go ahead and do a mini-tutorial on how to use a Digital Multimeter.


So what is a Digital Multimeter anyway, and what does it do?, a Digital Multimeter is a piece of Electronic Test Equipment that is used to measure various quantities, such as Resistance, Voltage, and Current in an Electrical Circuit.


Why do we need one?, because a Digital Multimeter is very useful when it comes to fault-finding or troubleshooting an Electrical Circuit.


Here's an example of an inexpensive Digital Multimeter:





If memory serves me right, I bought it from Dick Smith Electronics quite a few years ago, I actually bought three since they were on special at about $16.00 each.


In the pic above you will notice that there are two coloured probes plugged into the Multimeter, one is Red, and the other is Black, the Black probe is normally plugged into a socket marked "Com" (short for Common), and the Red probe can be plugged into either the socket marked "A" (Amps), "V" (Volts), or "Ohms" (sometimes marked with a horseshoe-shaped symbol).

If we want to measure Resistance in a circuit, or component, such as a pot, we plug the Red probe into the Ohms socket.

If we want to measure Voltage in a circuit, or for example a battery, we plug the Red probe into the Volts socket.

And if we want to measure the Current in a circuit, we plug the Red probe into the Amps socket.


Now, on the Multimeter itself, you can see a big rotary multi-position switch marked with various ranges of Voltage, Current, and Resistance.


For this mini-tutorial, I'm going to concentrate on just the Resistance and Voltage ranges, since they will probably be the most used when building guitars.


Here's an example to illustrate how to use a Multimeter to measure Resistance, in the following pic I have set it up to measure the Resistance of a 500k A (Log, or Audio) pot, I have the tip of the Red probe touching one of the outer solder-lugs, and the Black probe touching the other solder-lug, the middle solder lug is the wiper connection.


Because the pot is a 500k Log I have set the rotary switch to the 20M (20 Mega-Ohm) range.


The display shows the actual Resistance of the pot, in this case it is about 580k, or 580,000 Ohms, which is normal.





And here's an example to illustrate how to use a Multimeter to measure Voltage, in the following pic I have set it up to measure the voltage in a standard Alkaline 9V battery as used in a lot of FX pedals for guitars and Basses, here, I have set it up so that the tip of the Red probe is touching the battery's + (Positive) terminal, and the tip of the Black probe is touching the - (Negative) terminal.


Because the battery is a 9V type, I have set the rotary switch to the 20 V DC (Volts D.C.) range.


The display is showing the actual voltage-reading of the battery, about 9.59 Volts, the battery is a brand new fresh one straight out of the package, it is normal for a new 9V battery to measure that much.

[wokkaboy]

good stuff Doc, good tutorial for anyone new to multimeters

[DrNomis_44]

good stuff Doc, good tutorial for anyone new to multimeters

Cheers Wokka, in this tutorial, I could have included a bit of Electronic Theory, but I deliberately kept it simple so it's easy to understand.

[fender3x]

Amazing what you can do with an inexpensive meter. We'll done! I test all my pots before putting them in an ax. Never trust the stamp. I have tested a small mountain of batteries. But probably the single thing I have used it for most is to test continuity. Especially to make sure everything is properly grounded.

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[andrewdosborne]

Thanks Doc. Being completely inept at electronics I've never really understood or used my multimeter so appreciate the tutorial

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[wokkaboy]

Doc/Fender3X, what is the easiest way to know a circuit is earthed correctly ?

[DrNomis_44]

Doc/Fender3X, what is the easiest way to know a circuit is earthed correctly ?

The easiest way I can think of is in this example, suppose you want to check if the bridge on your guitar is correctly earthed, what you would do is set your multimeter to a low-ohms range, say 200 Ohms, you would then touch one of the probe tips to the bridge, and the other to a convenient ground-point, like the sleeve contact of the output-jack, if you got a reading of 0.02 then that would indicate that there was continuity between the bridge and ground, a reading like OL would indicate no continuity, or high-resistance greater than 200 Ohms.

[DrNomis_44]

Thanks Doc. Being completely inept at electronics I've never really understood or used my multimeter so appreciate the tutorial

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No worries at all mate, glad it was helpful.

[FredA]

The easiest way I can think of is in this example, suppose you want to check if the bridge on your guitar is correctly earthed, what you would do is set your multimeter to a low-ohms range, say 200 Ohms, you would then touch one of the probe tips to the bridge, and the other to a convenient ground-point, like the sleeve contact of the output-jack, if you got a reading of 0.02 then that would indicate that there was continuity between the bridge and ground, a reading like OL would indicate no continuity, or high-resistance greater than 200 Ohms.

Great tutorial Doc!
Might be good to mention the continuity testing function too (you may be on it as I type).
I use it a lot when testing / troubleshooting circuits as you don't need to watch the meter, the beep tells you when you have continuity, so you can quickly probe around.


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[DrNomis_44]

Yes, as FredA said in his post, some Multimeters do feature a Continuity-test function where Continuity is indicated by an audible beeping sound, this enables you to keep your eyes on where you put the tips of the probes rather than what's on the display, if you can afford a Digital Multimeter that features a Continuity-test function, definitely buy it.