Hi this is Ben Finio with Science Buddies. In this video we'll show you how
to use a multimeter.
Multimeters come in all shapes and sizes. While professional multimeters can cost
hundreds of dollars, if you're a student doing a science project or hobbyist
just tinkering with electronics, a cheaper multimeter somewhere in the
twenty to thirty dollar range is probably all you need. Most multimeters
have similar features including a screen that displays the readings, a knob that
selects the measurement, and ports where you plug in the probes to take the
measurement. In this video we'll be using this DT830L digital multimeter which
is included in many of our Science Buddies kits. We'll go over how to
measure voltage, current, resistance, and do a continuity check, some of the most
common features you'll use on a multimeter. Other multimeters might have
more advanced features like the ability to measure capacitance but we won't be
going over those in this video. Most multimeters come with a pair of red
and black probes with a plug on one end to go into the multimeter and a pointy
probe tip on the other end that you can use to probe circuits. It's convenient to
have some alligator clip cables handy as those can allow you to clip onto the
circuit to take measurements so your hands can be free to do other things.
There are different types of probe accessories available, for example these
probes have a banana plug on one end to go in the multimeter and an alligator
clip directly on the other end instead of a probe tip so you don't need a
separate alligator clip cable. Let's start by looking at our multimeter in a
little more detail. There are a lot of symbols on the front that might be kind
of overwhelming and confusing at first but don't worry we'll go over them one
by one as we use them. The main symbols you'll be seeing in this video are V for
volts, A for amperes which is the unit of current, and the capital Greek letter
Omega which stands for ohms or the unit of resistance. This multimeter has a
separate on/off switch that you use to turn the multimeter on and off. More
expensive multimeters usually have an auto power off feature that will turn it
off automatically after a certain period of inactivity, but this one doesn't so make
sure you remember to turn it off when you're not using it in order to conserve
the battery. Now let's look at the ports where we can plug the probes into the
multimeter. You'll see that we have three different ports labeled COM, V Omega mA,
and 10A. COM stands for common that's where the black probe is going to be
plugged in and we'll usually connect that to the ground or negative side of our
circuit. V Omega mA stands for volts ohms or
milliamps, we plug the red probe into this port for most of the measurements
we're going to be taking to measure voltage, resistance, or small amounts of
current, and then finally this third one we're not going to use as often that's
for measuring large amounts of current up to about 10 amps. So for now we're
going to plug the red probe into this V Omega ma port. Now let's start with the
relatively simple case of measuring the voltage of a battery. I'm going to set
the dial on my multimeter up here somewhere in the V range, we're not going
to worry about the exact number yet, turn the multimeter on, and again I have the
black probe plugged into the COM port and the red probe plug into the V
Omega milliamp port. I have two batteries here a double a and a 9-volt, and I'm
going to start out with the double a. I'm going to take,
oops, the black probe and touch it to the negative side of the battery and the red
probe and touch it to the positive side of the battery. And you can see I'm
getting a reading of zero zero one on the screen. And that's not a very
accurate reading I'm not getting any decimal places and you'll see that I
have my knobs set all the way up here to a thousand volts which if you know
anything about batteries is much much higher than we expect to get from a
double-a battery, we would expect this to be about 1.5 volts. So fancier
multimeters will have an auto ranging feature where they will automatically
select the measurement range for you. This multimeter isn't going to do that
for you, you need to manually select the range that is the best for what you want
to measure. So what I'm going to go do is go down a step to 200 volts and try
again. And now I'm getting 1.5 volts which is about what I expect, but 200
volts is still a lot bigger than what I need to measure, so I'm going to keep
stepping down to the 20 volt range, and notice that when I do that I get an
extra decimal place, the decimal point moved over one. So now if I measure
I get one point 6 volts, 1.60. So my reading is getting more accurate so I
got an extra decimal place. This voltage is actually small enough that I can keep
going down. Now notice that the label here changed now I'm in the 2000 M range
which stands for 2000 millivolts. So now my reading is in millivolts instead of
volts, it's important to pay attention to the labels on the dial because they'll
tell you the units of your measurement. Now here I don't have a decimal place any
more, I'm getting 1608 millivolts, so as I keep going down my reading keeps getting
more and more accurate. If I go down too far though my range won't be high enough
to measure the voltage. So I've gone all the way down to be 200 millivolt range
and now I'm getting a one with no other numbers which, is how this multimeter
tells me that the reading is outside the current range I have selected. So if I go
down too far I'll get that one on the screen, I go back up to the next highest
value and that's going to give me my most accurate reading for this voltage.
So in this case I get one thousand six hundred and seven millivolts or one
point six oh seven volts. I can do the same thing for the 9-volt battery here
where you might be able to guess if I have this set to two thousand millivolts,
that's two volts, that range is not high enough so I get a 1. If I want to measure
that 9-volt battery I'm gonna need to go up the next step to 20 volts and here
you can see that this battery has actually actually been drained a little
bit, I'm only getting about seven point nine eight volts instead of the nine
volts I would expect. Finally if I reverse my probes so if I put the red
probe on the negative terminal and the black probe on the positive terminal, I
will just get a negative number. So that doesn't damage anything it doesn't hurt
anything, that just tells you that you have your probes backwards because you
would expect a positive voltage when measuring the battery. Now measuring the
voltage of a battery is pretty simple what if we want to measure the voltage
of something in a circuit? So here I have an example circuit consisting of a
battery pack a resistor and an LED, very simple demonstration circuit, and what if
I say I want to measure the voltage in this circuit? Now note that voltage is
measured between two points so it doesn't make sense to just ask what is
the voltage in this circuit, we have to ask which component we are measuring the
voltage of. In this case if we look at the circuit diagram we can see we have
three components in series, we have the battery, the resistor, and the LED, and we
can measure the voltage across any one of those components individually. To
measure voltage in circuit you connect the multimeter in parallel, so in this
case there are three different ways we could connect the multimeter in parallel
to something in this circuit. We could connect it in parallel to the battery, in
parallel to the resistor, or in parallel to the LED. When taking measurements on a
breadboard this is where alligator clips and jumper wires can come in handy
because you can just put the jumper wires into the breadboard and then your
hands will be free to do other things. If you don't understand how a breadboard
works or you've never used one before we highly recommend you check out,
check out our breadboard tutorial video which will tell you everything you need
to know about breadboards, but for now we're going to assume you know how they
work. So first I'm going to connect my two wires in parallel to the battery,
putting them into the power buses here. You'll see I get a reading of 2.83
volts. I can also connect them in parallel to
the LED.
I get a smaller reading of 2.2, roughly about 2.3 volts and finally I can
connect them in parallel to the resistor
and I get a reading of about 0.65 volts so as I would expect with these
components in series the voltage across the LED plus the voltage across the
resistor should equal the voltage across the battery pack. Now what if I want to
measure the current through this circuit? This gets a little more complicated. To
measure the current through a part of a circuit you need to put the multimeter
in series with that part of the circuit. And while to measure voltage I didn't
actually need to rearrange anything on the breadboard to do that because I was
just putting the multimeter probes in parallel with the different circuit
components, to put the multimeter in series I'm actually going need to
rearrange things on the breadboard a bit. So if I look at the circuit diagram, I
only have one loop in my circuit here so the current I measure is going to be the
same regardless of where I put the multimeter. I could put it in between the
battery and the resistor, in between the resistor and the LED, or in between the
LED and the battery, the current will be the same in any case. But when I
go do that on the breadboard here I'm going to need to move one of the parts.
So for example I'm going to move the resistor lead over one hole here and
then get ready to put my multimeter probes in series with the resistor and
the LED, but before I do that I want to be careful. Let's go back and look at the
ports for the probes on our multimeter again and the settings for current.
Remember we have this extra port for 10 amps and if you don't know how much
current you're going to measure it's always safer to start with that 10 amp
setting because that will allow you to measure a much higher current without
damaging your multimeter's fuse. So if you know about LEDs you might know oh that's
probably only a couple tens of milliamps, you should probably be safe, but
especially if you're working with motors, or something where you just in general
don't know the current, it's safer to start with that higher measurement
because as you can see if you look at the small print by this other port here
that one is limited to 500 milliamps max, so if we exceed 500 milliamps on this
port we're going to blow the fuse. So we can go all the way up to 10 amps on this
one, safer to start there and we're going to
turn our dial over to the 10 amp setting on the knob. So now I should be able to
put my multimeter in series, you notice that the LED has
gone out because I broke the circuit by moving that resistor.
I put the multimeter in series here, the LED goes back on but I'm getting a
pretty inaccurate reading again, 0.01, I don't know what the decimal points are
beyond that so it should be safe now to move down to the port with the lower
current range that's going to be more accurate. So I'm going to switch back
down to here, lower myself to the 200 milliamps setting and you can see now
I'm getting a more accurate reading of thirteen point seven, thirteen point
eight milliamps. And just like I did with the voltage I can keep stepping down to
get more and more accurate readings until my range goes too low. So I can
step down to 20 milliamps, now I'm getting an extra decimal place about
twelve point two one, all the way down to 2,000 milliamps and now I've gone too
low. Okay so if I go back up to about 20 milliamps that's gonna be the most
accurate reading I can get for this circuit with two decimal places. Now when
you are done measuring current it is always a good idea to set your
multimeter dial back to measuring voltage, and that's because it is much
easier to accidentally blow the fuse when you have a multimeter set to
measure current. For example if you wanted to measure the voltage of a
battery like we did earlier, and you connected the probes directly to the
battery with no resistance in series to limit the current while you have it set
to measure current you will easily blow the fuse because you're going to get a
lot more than 500 milliamps directly out of the battery. So again when you're done
measuring current set it back to voltage just to be safe
the next time you pick up the multimeter. Okay next let's talk about measuring
resistance, so this is something that's convenient if you just hate reading
those color codes on the tiny little resistors or if you need to measure the
actual value of your resistor instead of just a rated value because there's
usually a pretty big error range like 5 or 10% on the actual value of the
resistor. So to do that you're going to want to remove the resistor from the
circuit don't try to measure resistance while the resistor is connected to a
power supply in an active circuit or you won't get an accurate reading, and
again here's where alligator clips come in handy
to just clip on to the leads of that resistor and just like we did with
voltage and current, you can make an educated guess as to where you should
start on this dial, so for ohms we can go all the way up to 2000 kilo ohms which
is equivalent to 2 mega ohms or all the way down to 200 ohms. In this case I
started at the lower end of the range and I have what should be a 47 ohm
resistor here, so I'm getting pretty close to that, about forty six point
eight, forty six point nine ohms and you can see as I go up I start to lose
accuracy because I'm losing that decimal place. So measuring a resistor this small,
I want to be all the way down there in that two hundred ohm range I have a
bigger resistor here, this one is supposed to be about ten kilo ohms
so if I connect that,
you can see I'm getting the one because I'm outside the range of exceeded two
hundred ohms and as I start going up eventually I should get in the proper
range for this resistor. So you can see again there's that error percentage this
is actually about ten point three ohms not exactly,
sorry ten point three kilohms not exactly ten kilo ohms, so it can be
important depending on what you're doing to measure the actual value of your
resistors. Now with cheaper multimeters you're not going to get very accurate
readings for very small resistances, so if you're trying to measure something
just like a wire this is usually probably down around one ohm or even
less than that, don't trust those readings too much. You can see I can
connect to this wire and go down to my smallest range and I get something like
1.0 ohms but really below and ohm your reading is not going to be very accurate
with a cheap multimeter so make sure you use this to measure actual resistors but
not just pieces of conductive metal or wires. The final feature we're going to
go over is the continuity check so that's this little symbol here with kind
of those little curvy lines and the arrow symbol which represents a diode if
you know what a diode is, and this one is a really convenient feature that just
beeps if two things are electrically connected. So if I touch my probes
together directly [beeping] it beeps at me because there's a complete conductive path for
the circuit or the current to flow through the circuit there. This is a
really convenient feature to check if two things are connected like they're
supposed to be in your circuit or for example to check if a cable is good. So
for example let's take my circuit here, put my resistor back in
and say I don't know if maybe I have something wired improperly I want to
make sure that there's a conductive path between this leg of my LED and this wire
on the battery [beeping] so that's telling me that there is a path between this part of the
LED and there. So say I had this wired improperly, say had the resistor in the
wrong hole, and my LED is not lighting up, then I can test both sides of my LED. I
can test here and say okay I know [beeping] I have conductivity on this side those are
connected because I'm getting a beep, but if I test on this side there should be a
connection between the LED and the resistor, but I'm not getting a beep
there. Then if I look more closely I could realize, oh I have that wired
improperly I don't have conductivity between this leg of the LED and this leg
of the resistor. Similarly say you have an experiment with a bunch of wires or
cables and you're not sure if maybe you kinked a cable or broke something or if
you have a cable that's going bad yeah if I take this alligator clip and touch
the probes to both ends the alligator clip [beeping] I'll get a beep letting me know
that my cable is good if I didn't get a beep and I'd know that this cable is
probably bad. So again, a convenient feature that you can use to test for
conductivity in circuits or test if a material is conductive. For example if I
touch these two probes to a piece of metal say like the outside surface of
this battery [beeping] I know that's conductive but if I touch it to the paper on my
work surface here that's not conductive because paper does not conduct
electricity. So also a convenient check to test if a material is conductive or
not. Again there are some more advanced features on this and other multimeters
that we didn't go over in this video, you might have noticed this NPN and PNP
thing down here that's for measuring transistors, there's a V with a squiggly
line next to it for measuring alternating current instead of direct
current. You can measure the voltage from a wall outlet, we don't recommend doing
that if you're new to electronics because wall outlets are actually
dangerous and you can hurt yourself if you don't know what you're doing, whereas
the electricity from batteries and little battery-powered circuits like
this is generally pretty harmless, so this is much safer if you're starting
out. We're not going to go over those in this
video but if you have any more questions about anything you saw in the video in
more detail we recommend you check out our written tutorial, there's a link to
that at the end of the video and have fun using your multimeter in your
project.