How to Use a Multimeter

Hi, I'm Ben Finio from Science Buddies. In this video we will show you how to use a

multimeter

. Multimeters come in all shapes and sizes. While professional

multimeter

s can cost hundreds of dollars, if you're a student doing a science project or a hobbyist just playing with electronics, a cheaper multimeter in the twenty to thirty dollar range is probably all you need. Most multimeters have similar features including a screen that shows the readings, a knob that selects the measurement, and ports where the probes are connected to take the measurement. In this video we will use this DT830L digital multimeter that is included in many of our Science Buddies kits.

We'll go over how to measure voltage, current, resistance, and perform a continuity check, some of the most common functions you'll use on a multimeter. Other multimeters may have more advanced features, such as the ability to measure capacitance, but we won't discuss them in this video. Most multimeters come with a pair of red and black probes with a plug on one end to enter the multimeter and a pointed probe tip on the other end that you can use to probe circuits. It's a good idea to have some wires with alligator clips on hand, as they can allow you to clip them to the circuit to take measurements and keep your hands 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 into the multimeter and an alligator clip directly on the other end instead of a probe tip, so you don't need a alligator clip cable separately. . Let's start by looking at our multimeter in a little more detail. There are a lot of symbols on the front that can be overwhelming and confusing at first, but don't worry, we'll go through them one by one as we use them. The main symbols you'll see in this video are V for volts, A for amperes, which is the unit of current, and the capital Greek letter Omega, which means ohms or the unit of resistance.

This multimeter has a separate on/off switch that is used to turn the multimeter on and off. More expensive multimeters usually have an auto-off feature that will automatically turn them off 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 to conserve battery. Now let's look at the ports where we can connect the probes to the multimeter. You will see that we have three different ports labeled COM, V Omega mA and 10A. COM means common, that is where the black probe will be connected and we will usually connect it to ground or the negative side of our circuit.

V Omega mA means volts ohms or milliamps, we connect the red probe to this port for most of the measurements we are going to take to measure voltage, resistance or small amounts of current, and finally this third one we will not use as often to measure large amounts of current, up to approximately 10 amperes. So for now we're going to connect the red probe to 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 here somewhere in the V range, we're not going to worry about the exact number yet, I turn on the multimeter and again I have the black probe connected to the COM port and I connect the red probe to the milliamp V port Omega.

I have two batteries here, one double a and one 9 volt, and I'm going to start 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 that 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 decimals, and you'll see that I have my knobs set up here to a thousand volts, which, if you know anything about batteries, is a lot higher than we expect. get from a double a battery, we would expect it to be about 1.5 volts.

Therefore, more sophisticated multimeters will have an auto-range feature where they will automatically select the measurement range for you. This multimeter won't do that for you, you have to manually select the range that is best for what you want to measure. So what I'm going to do is go down a step to 200 volts and try again. And now I'm getting 1.5 volts, which is pretty much what I expected, but 200 volts is still a lot bigger than what I need to measure, so I'll keep going down to the 20 volt range, and notice that when I do that, I get one additional decimal, the decimal point moved more than one.

Now if I measure I get a point of 6 volts, 1.60. So my reading is getting more accurate, so I got an extra decimal. In reality, this voltage is small enough that it can be lowered further. Now notice that the label here has changed now that I'm in the 2000 M range, which means 2000 millivolts. Now that my reading is in millivolts instead of volts, it's important to pay attention to the labels on the dial because they will tell you the units of measurement. Now here I no longer have a decimal place, I get 1608 millivolts, so as I keep going down, my reading becomes more and more accurate.

If I go too low, my range won't be high enough to measure voltage. So I went down to the 200 millivolt range and now I get one with no other numbers, that's how this multimeter tells me that the reading is outside the current range I have selected. So if I go too low, that will appear on the screen, I go back to the next higher value and that will give me my most accurate reading for this voltage. So in this case I get one thousand six hundred seven millivolts or one point six oh seven volts. I can do the same thing with the 9 volt battery here, where you can 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 volts. I'm going to need to go up to the next step to 20 volts and here you can see that this battery has actually run down 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, if I put the red probe on the negative terminal and the black probe on the positive terminal, I will get a negative number. So that doesn't hurt anything, it doesn't hurt anything, that just tells you that you have the probes backwards because you would expect a positive voltage when measuring the battery.

Now, measuring the voltage of a battery is quite simple. What happens if we want to measure the voltage of something in a circuit? Here I have an example circuit consisting of a battery, a resistor and an LED, a very simple demo circuit, and what if I say I want to measure the voltage in this circuit? Now keep in mind that voltage is measured between two points, so there is no point in simply asking what the voltage is 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 that we have three components in series, we have the battery, the resistor and the LED, and we can measure the voltage on any of those components individually.

To measure the voltage in the circuit the multimeter is connected in parallel, so in this case there are three different ways in which we can 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 board, this is where alligator clips and jumper cables can come in handy because you can simply attach the jumper cables to the board and then your hands will be free to do other things. If you don't understand how a breadboard works or have never used one before, we highly recommend checking 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 do they work.

First I'm going to connect my two cables in parallel to the battery, placing them here on the power buses. You will see that 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, 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 you would expect with these components in series, the voltage at across the LED plus the voltage across the resistor should equal the voltage across the battery pack. Now what happens 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 it is necessary to put the multimeter in series with that part of the circuit. And although to measure the voltage I didn't need to rearrange anything on the board to do it because I was simply placing the multimeter probes in parallel with the different components of the circuit, to put the multimeter in series I will actually need to rearrange things on the board a bit. evidence. So if I look at the circuit diagram, here I only have one loop in my circuit, so the current I measure will be the same regardless of where I place the multimeter.

You could put it between the battery and the resistor, between the resistor and the LED, or between the LED and the battery, the current will be the same in either case. But when I do that on the board here, I'm going to need to move one of the parts. So, for example, I'm going to move the resistor wire over a hole here and then I'm going to prepare to put the 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 again at the ports for the probes on our multimeter and the current settings.

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 the multimeter. fuse. So if you know about LEDs, you might know that it'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 generally don't know the current, it's It's safer to start with that higher measurement because as you can see, if you look at the fine print on this other port here, that one is limited to 500 milliamps maximum, so if we exceed 500 milliamps on this port, we're going to burn out. the fuse. .

So we can go up to 10 amps on this one, it's safer to start there and we're going to turn our dial to the 10 amp setting on the knob. So now I should be able to put my multimeter in series, you notice the LED went out because I broke the circuit by moving that resistor. I put the multimeter in series here, the LED comes back on but I get a pretty inaccurate reading again, 0.01, I don't know what the decimal points are beyond that, so now it should be safe to go down to the port. with the lower current range it will be more accurate.

So I'm going to go back down here, go down to the 200 milliamp setting and now you can see 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 lowering it to get more and more accurate readings until my range drops too low. So I can go down to 20 milliamps, now I get an extra decimal around twelve point two one, down to 2000 milliamps and now I'm down too far. Well, if I go back up to about 20 milliamps, that will be the most accurate reading I can get for this circuit to two decimal places.

Now, when you're done measuring current, it's always a good idea to set the multimeter dial back to measuring voltage, and that's because it's much easier to accidentally blow the fuse when you have a multimeter set to measure current. . For example, if you want to measure the voltage of a battery like we did before and connect the probes directly to the battery without a series resistor to limit current while you have it set to measure current, you will easily blow the fuse because you will get much more than 500 milliamps. directly from the battery. So again, when you're done measuring the current, set it back to voltage just to be safe the next time you pick up the multimeter.

Okay, now let's talk about measuring resistance, so this is something that's convenient if you just hate reading those color codes on the little resistors or if you need to measure the actual value of your resistor instead of just a nominal value because there's usually a nice Large error range like 5 or 10% on the real value of the resistor. So to do that you'll want to remove the resistor from the circuit, don't try to measure the resistance while the resistor is connected to a power source in an active circuit or you won't get an accurate reading, and again this is where alligator clips come in handy. to hook the leads on that resistor and just like we did with voltage and current, you can make an educated guess about 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 up 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 gettinggetting pretty close to that, around forty-six point eight, forty-six point nine ohms and you can see how I go up and start to lose precision because I'm losing that decimal. So measuring a resistance this small, I want to be all the way in that two hundred ohm range. I have a larger resistor here, this one is supposed to be about ten kiloohms, so if I plug it in you can see I'm getting the right one because I'm out of the range of going over two hundred ohms and when I start going up eventually it should be in the suitable range for this resistance.

So you can see again that there is a percentage of error, it's actually around ten point three ohms, not exactly, sorry, ten point three kiloohms, not exactly ten kiloohms, so it may be important, depending on what you're into. doing, measure the real value of your resistors. Now, with cheaper multimeters you won't get very accurate readings for very small resistances, so if you're trying to measure something like a wire, this is probably around an ohm or even less, don't trust it. those readings too much. You can see I can plug into this cable and go down to my smallest range and I get something like 1.0 ohms, but actually below ohms your reading won't be very accurate with a cheap multimeter, so make sure you use that to measure. the real value. resistors, but not just conductive metal parts or wires.

The final feature we're going to go over is the continuity check, so that's this little symbol here with those little curved lines and the arrow symbol that represents a diode if you know what a diode is, and this one is really convenient. Feature that only beeps if two things are electrically connected. So if I touch my probes directly, it beeps because there is a complete conductive path for the circuit or current to flow through the circuit there. This is a really convenient feature to check if two things are connected as they are supposed to be in your circuit or, for example, to check if a cable is in good condition.

So, for example, let's take my circuit here, let's put my resistor back in and say: I don't know if maybe I have something connected incorrectly. I want to make sure there is a conductive path between this leg of my LED and this battery cable. That tells me that there is a path between this part of the LED and there. So let's say I had this wired incorrectly, let's say I had the resistor in the wrong hole and my LED doesn't turn on, then I can test both sides of my LED. I can try here and say, "Okay." I know I have conductivity on this side.

These are connected because I get a beep but if I test on this side there should be a connection between the LED and the resistor but no. getting a beep there. Then if I look closer I can realize that I have that connected incorrectly. I have no conductivity between this leg of the LED and this leg of the resistor. Similarly, let's say you have an experiment with a bunch of wires or cables and you're not sure if maybe you bent a wire or broke something or if you have a wire that's going bad, yeah, if I take this alligator clip and play the probes in both. ends the alligator clip, I will hear a beep letting me know that my cable is good, if I didn't get a beep I would know that this cable is probably defective.

Again, a convenient feature that you can use to test conductivity in circuits or test if a material is conductive. For example, if I touch these two probes to a piece of metal, let's say like the outside surface of this battery, I know that it's conductive, but if I touch the paper on my work surface here, that's not conductive because paper doesn't conduct electricity. . It is also a convenient check to check whether a material is conductive or not. Again, there are some more advanced features on this and other multimeters that we didn't discuss in this video. You may have noticed this NPN and PNP thing down here that is for measuring transistors, there is a V with a wavy line next to it to measure alternating current instead of direct current.

You can measure voltage from a wall outlet, we don't recommend doing this if you are new to electronics because wall outlets are really dangerous and you can get hurt if you don't know what you are doing, while electricity from batteries and small battery powered circuits like this is usually pretty harmless, so it's much safer if you're just starting out. We're not going to go over them in this video, but if you have more questions about something you saw in the video in more detail, we recommend you check out our written tutorial, there's a link at the end of the video and have fun using your multimeter in your project.