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:


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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.


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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.


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[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.

[Dedman]

Thanks Doc, Just what I need to go trouble shooting tomorrow

[tonyw]

Good on you Doc, well done.

I carry my meters around everywhere, each one is setup for individual tasks, i dont have time to mess around with settings. Saves me doing anything more than turning on and maybe switching 1 notch or 2, but it gets expensive having a few of them.

[fender3x]

On continuity, the test for ground/earth is also a continuity test that you can do with a cheap meter.

Set the meter on one of the ohms settings and turn it on. It will register 1 with the test leads not touching. When you touch them together it should register close to 0. Touched together is continuity. So, to test the continuity of a wire, touch one lead to each end of the wire. If it registers close to 0 it's good. If the register stays on 1 you have a break.

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[DrNomis_44]

If you only have an older style Analog Multimeter you can still use it to do Continuity Tests, all you need to do is switch it to a low-Ohms range, such as X1, or X10, then touch the two probes together, then use the Zero-Adjust to Zero the Meter-Needle, you can then test for continuity as per a Digital Multimeter, Continuity will be indicated by the Meter-Needle ending up fairly close to the Zero mark on the Meter Scale.

[fender3x]

I love those old analog meters and often use them for testing continuity. When you have it you really see the needle zip across the meter.

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[DrNomis_44]

I love those old analog meters and often use them for testing continuity. When you have it you really see the needle zip across the meter.

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Yep, in some ways I reckon the Analog Multimeter is better for doing Continuity Tests because they usually have a 1.5V battery inside them which is used to provide the test-current when measuring resistance, Digital Multimeters do a similar thing but the test current is smaller due to the fact that Digital Multimeters typically have an input resistance of about 10 Million Ohms so that there's no loading on the circuit being tested, on the other hand an Analog Meter's input resistance can be something like 10 or 20 Thousand Ohms per Volt, this will load a circuit being tested.

[Muzza]

A visual explanation of Volts, Current and Resistance...

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[DrNomis_44]

A visual explanation of Volts, Current and Resistance...

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Cheers Muzza, that is a great diagram for explaining Voltage, Current, and Resistance, another analogy is to think of water flowing through a pipe, the Voltage would be the pressure that's forcing the water through the pipe, Current would be how much water is flowing through the pipe at any one point along the length of the pipe, and Resistance would be the diameter of the pipe, so, if we decrease the diameter of the pipe (increasing Resistance) the water will have a harder time flowing through it than if the pipe was bigger in diameter, if we had a large diameter pipe (low Resistance) and increased the pressure (higher Voltage) forcing the water to flow through the pipe, then more water would flow past a given point along the length of the pipe (higher Current).


This goes to show that Voltage, Current, and Resistance are inter-related in an Electrical Circuit, as Ohm's Law states:


E (Voltage)= I ( Current) X R ( Resistance)

[fender3x]

I have always heard the water analogy, but I have to admit that I really like:

Kicking-guy = stuck-in-tunnel-guy + guy-pulling-rope

[DrNomis_44]

I have always heard the water analogy, but I have to admit that I really like:

Kicking-guy = stuck-in-tunnel-guy + guy-pulling-rope



That "+" should really be an "X".



I didn't really intend to include some mathematics with this mini-tutorial, I really wanted to keep it relatively simple to understand for people new to Electronics, but at some stage you're probably going to have a situation where knowing Ohm's Law, and how to work with it, will be useful, and, or, essential.

[DrNomis_44]

Hi everyone, just as a little addendum to my Multimeter Mini-Tutorial, if you have an Analogue Needle-style Multimeter, here's the procedure you need to follow before you do a resistance measurement:


Assuming that the meter has a good fresh battery installed:


1, Switch the meter to an appropriate resistance range, X1 or X10 is a good choice if you are doing continuity checks.

2, Touch the tips of the two meter probes together, the meter needle will swing to the right towards the Zero-mark on the meter scale, it may also come to a stop before or after the Zero-mark.

3, Next, rotate the Zero-Adjust knob one way or the other to get the meter needle to sit right over the Zero-mark on the meter scale, this compensates for the small amount of resistance that the meter leads contribute to the resistance reading, it also compensates for the battery gradually going flat too.

4, Proceed to doing the continuity checks, continuity will be indicated by the meter needle coming to a rest near the zero-mark.

[corsair]

This community is just brilliant, I have to say... I know how to use a DMM but seeing this is great as there are many out there who are unsure of exactly how to use one! I have a pro quality job out in my tech tools drawer but there is a basic Dick Smith one in the junk/tool drawer in the kitchen that everyone in the family knows how to use to check DC battery voltages and continuity in basic circuits, and yes... they all know not to stick the probes into power sockets!! :-)

Thanks to DrNomis for putting this up!!

[DrNomis_44]

This community is just brilliant, I have to say... I know how to use a DMM but seeing this is great as there are many out there who are unsure of exactly how to use one! I have a pro quality job out in my tech tools drawer but there is a basic Dick Smith one in the junk/tool drawer in the kitchen that everyone in the family knows how to use to check DC battery voltages and continuity in basic circuits, and yes... they all know not to stick the probes into power sockets!! :-)

Thanks to DrNomis for putting this up!!


You are most welcome.

[Simon Barden]

Some multimeters (again, not expensive ones) also have a capacitance testing mode. Useful if you have a selection of similar value capacitors but want to find one that's closest to the value you need. A lot of the cheaper capacitors have a ±20% manufacturing tolerance, and even more expensive ones are ±10%, so if you want to fit one to a tone control circuit and have bought a pack of 10, then it's worth testing them all out and using the one closest to your design value.

Meters with this function have a couple of slots to stick the capacitor legs in. They have spring contacts inside the slots, so they will hold the capacitor in place (though you may have to bend the capacitor's legs to fit). Again, unless you have an expensive auto-ranging capacitor, you'll need to select the correct capacitance range on the meter, so it's best to make sure you're familiar with milli-, micro-, nano- and pico- farad terminologies (mF, μF, nF and pF) and equivalent values e.g. 0.022 microfarads is the same as 22 nanofarads.

With all but electrolytic capacitors (tubular shaped ones, normally with a line of "+++++" on one side to indicate the +ve connection leg) it doesn't matter what way round you stick them in. Electrolytics aren't normally used in tone circuits but if you do ever need to test one for something else, just make sure the +ve leg goes into the +ve slot to get a correct reading.

[DrNomis_44]

Some multimeters (again, not expensive ones) also have a capacitance testing mode. Useful if you have a selection of similar value capacitors but want to find one that's closest to the value you need. A lot of the cheaper capacitors have a ±20% manufacturing tolerance, and even more expensive ones are ±10%, so if you want to fit one to a tone control circuit and have bought a pack of 10, then it's worth testing them all out and using the one closest to your design value.

Meters with this function have a couple of slots to stick the capacitor legs in. They have spring contacts inside the slots, so they will hold the capacitor in place (though you may have to bend the capacitor's legs to fit). Again, unless you have an expensive auto-ranging capacitor, you'll need to select the correct capacitance range on the meter, so it's best to make sure you're familiar with milli-, micro-, nano- and pico- farad terminologies (mF, μF, nF and pF) and equivalent values e.g. 0.022 microfarads is the same as 22 nanofarads.

With all but electrolytic capacitors (tubular shaped ones, normally with a line of "+++++" on one side to indicate the +ve connection leg) it doesn't matter what way round you stick them in. Electrolytics aren't normally used in tone circuits but if you do ever need to test one for something else, just make sure the +ve leg goes into the +ve slot to get a correct reading.



Cheers for that, I bought a Digital Multimeter from Dick Smith Electronics a few years ago, which also included an Inductance measuring function as well as Capacitance and Frequency, it cost me about $99.00, but it stopped working so I have been looking for a good replacement that offered the same range of functions.

[Simon Barden]

Mine wasn't expensive, maybe £25/A$42. I can no longer find it on the web site of the store I got it from maybe 2 years ago, Maplin, (our equivalent of Jaycar) but they have ones with similar functions, for a similar price (Jaycar seem to have similar looking meters for similar prices). I find they often have them marked down in sales.

[DrNomis_44]

Mine wasn't expensive, maybe £25/A$42. I can no longer find it on the web site of the store I got it from maybe 2 years ago, Maplin, (our equivalent of Jaycar) but they have ones with similar functions, for a similar price (Jaycar seem to have similar looking meters for similar prices). I find they often have them marked down in sales.


I also have a 25Mhz Dual Trace Oscilloscope which I sometimes use to trace out signals in one of my Pedal builds, I bought it new from Dick Smith Electronics back in the late 90's, back then, it cost me around $700.00 or so, it's a great bit of test gear, I also have a small single-trace 10Mhz Oscilloscope, next year I'm going to look at buying a new Digital Oscilloscope , and I'll also start ordering some new components for a Soldano SLO 50 amp head I'm going to be working on, the chassis is currently sitting on top of my Marshall amp, it uses five 12AX7 twin-triodes, and two EL34 power pentodes, should sound pretty cool once it's finished and working.