How To Use A Multimeter

How To Use A Multimeter

                       Figure 1. A typical multimeter.

This section includes answers to the following questions:

• What is a multi meter?
• What can multi meters measure?
• What are voltage, current, and resistance?
• What are direct current (DC) and alternating current (AC)?
• What are series and parallel circuits?
• What do all the symbols on the front of the multimeter mean?
• What are the red and black wires (probes)? Where do I plug them in?

What is a multimeter?

A multimeter is a handy tool that you use to measure electricity, just like you would use a ruler to measure distance, a stopwatch to measure time, or a scale to measure weight. The neat thing about a multimeter is that unlike a ruler, watch, or scale, it can measure different things — kind of like a multi-tool. Most multimeters have a knob on the front that lets you select what you want to measure. Below is a picture of a typical multimeter. There are many different multimeter models; visit the multimeter gallery for labeled pictures of additional models.

Education Name: How To Use A Multimeter 

Watch Use A Multimeter Online HD

What can multimeters measure?

Almost all multimeters can measure voltage, current, and resistance. See the next section for an explanation of what these terms mean, and click on the Using a Multimeter tab, above, for instructions on how to make these measurements.

Some multimeters have a continuity check, resulting in a loud beep if two things are electrically connected. This is helpful if, for instance, you are building a circuit and connecting wires or soldering; the beep indicates everything is connected and nothing has come loose. You can also use it to make sure two things are not connected, to help prevent short circuits.

Some multimeters also have a diode check function. A diode is like a one-way valve that only lets electricity flow in one direction. The exact function of the diode check can vary from multimeter to multimeter. If you're working with a diode and can't tell which way it goes in the circuit, or if you're not sure the diode is working properly, the check feature can be quite handy. If your multimeter has a diode check function, read the manual to find out exactly how it works.

Advanced multimeters might have other functions, such as the ability to measure and identify other electrical components, like transistors or capacitors. Since not all multimeters have these features, we will not cover them in this tutorial. You can read your multimeter's manual if you need to use these features.

What are voltage, current, and resistance?

If you haven't heard of these terms before, we'll give a very simple introductory explanation here. You can read more about voltage, current, and resistance in the References tab, above. Remember that voltage, current, and resistance are measurable quantities that are each measured in a unit that has a symbol, just like distance is a quantity that can be measured in meters, and the symbol for meters is m.

• Voltage is how hard electricity is being "pushed" through a circuit. A higher voltage means the electricity is being pushed harder. Voltage is measured in volts. The symbol for volts is V.
• Current is how much electricity is flowing through the circuit. A higher current means more electricity is flowing. Current is measured in amperes. The symbol for amperes is A.
• Resistance is how difficult it is for electricity to flow through something. A higher resistance means it is more difficult for electricity to flow. Resistance is measured in ohms. The symbol for ohms is Ω (the capital Greek letter omega).

Technical Note
The symbol that is used for a unit is usually different than the symbol for a variable in an equation. For example, voltage, current, and resistance are related by Ohm's law (see the References tab to learn more about Ohm's law):
$$Voltage=Current\times Resistance$$which is usually expressed as
$$V=IR$$In this equation, V represents voltage, I represents current, and R represents resistance. When referring to the units volts, amps, and ohms, we use the symbols V, A, and Ω, as explained above. So, "V" is used for both voltage and volts, but current and resistance have different symbols for their variables and units. Don't worry if this seems confusing; this table will help you keep track:

Variable          Symbol

Volts              V

Ampere            A

Ohm              Ω

Voltage            V

Current             I

Resistance        R 

This is very common in physics. For example, in many equations, "position" and "distance" are represented by the variables "x" or "d," but they are measured in the unit meters, and the symbol for meters is m.

A simple analogy to better understand voltage, current, and resistance: imagine water flowing through a pipe. The amount of water flowing through the pipe is like current. More water flow means more current. The amount of pressure making the water flow is like voltage; a higher pressure will "push" the water harder, increasing the flow. Resistance is like an obstruction in the pipe. For instance, a pipe that is clogged with debris or objects will be harder for water to flow through, and will have a higher resistance than a pipe that is free of obstruction.

What are direct current (DC) and alternating current (AC)?

Direct current (abbreviated DC) is current that always flows in one direction. Direct current is supplied by everyday batteries—like AA and AAA batteries—or the one in your cell phone. Most of the Science Buddies projects you do will probably involve measuring direct current. Different multimeters have different symbols for measuring direct current (and the corresponding voltage), usually "DCA" and "DCV," or "A" and "V" with a straight bar above or next to them. See "What do all the symbols on the front of the multimeter mean?" for more information about the abbreviations and symbols on multimeters.

Alternating current (abbreviated AC) is current that changes direction, usually many times in one second. The wall outlets in your house provide alternating current that switches directions 60 times per second (in the U.S., but 50 times per second in other countries). (Warning: Do not use a multimeter to measure the wall outlets in your home. This is very dangerous.) If you need to measure alternating current in a circuit, different multimeters have different symbols to measure it (and the corresponding voltage), usually "ACA" and "ACV," or "A" and "V" with a squiggly line (~) next to or above them.

What are series and parallel circuits?

When you take measurements with a multimeter, you will need to decide whether to attach it to your circuit in series or in parallel, depending on what you want to measure. In a series circuit, each circuit element has the same current. So, to measure current in a circuit, you must attach the multimeter in series. In a parallel circuit, each circuit measurement has the same voltage. So, to measure voltage in a circuit, you must attach your multimeter in parallel. To learn how to take these measurements, see the Using a Multimeter tab.

Figure 2 shows basic series and parallel circuits, without a multimeter connected. To learn more about voltage, current, and resistance in series and parallel circuits, check out the References tab.

Figure 2. In a basic series circuit (left), each element has the same current (but not necessarily the same voltage; that will only happen if their resistances are all the same). In a basic parallel circuit (right), each element has the same voltage (but not necessarily the same current; that will only happen if their resistances are all the same).

What do all the symbols on the front of the multimeter mean?

You might be confused by all the symbols on the front of your multimeter, especially if you don't actually see words like "voltage," "current," and "resistance" spelled out anywhere. Don't worry! Remember from the "What are voltage, current, and resistance?" section that voltage, current, and resistance have units of volts, amps, and ohms, which are represented by V, A, and Ω respectively. Most multimeters use these abbreviations instead of spelling out words. Your multimeter might have some other symbols, which we will discuss below.

Most multimeters also use metric prefixes. Metric prefixes work the same way with units of electricity as they do with other units you might be more familiar with, like distance and mass. For example, you probably know that a meter is a unit of distance, a kilometer is one thousand meters, and a millimeter is one thousandth of a meter. The same applies to milligrams, grams, and kilograms for mass. Here are the common metric prefixes you will find on most multimeters (for a complete list, see the References tab):

• µ (micro): one millionth
• m (milli): one thousandth
• k (kilo): one thousand
• M: (mega): one million

These metric prefixes are used in the same way for volts, amps, and ohms. For example, 200kΩ is pronounced "two hundred kilo-ohms," and means two hundred thousand (200,000) ohms.

Some multimeters are "auto-ranging," whereas others require you to manually select the range for your measurement. If you need to manually select the range, you should always pick a value that is slightly higher than the value you expect to measure. Think about it like using a ruler and a yardstick. If you need to measure something that is 18 inches long, a 12-inch ruler will be too short; you need to use the yardstick. The same applies to using a multimeter. Say you are going to measure the voltage of a AA battery, which you expect to be 1.5V. The multimeter on the left in Figure 3 has options for 200mV, 2V, 20V, 200V, and 600V (for direct current). 200mV is too small, so you would pick the next highest value that works: 2V. All of the other options are unnecessarily large, and would result in a loss in accuracy (it would be like using a 50-foot tape measure that only has markings every foot, and no inch markings; it isn't as accurate as using a yardstick with 1-inch markings).

Figure 3. The multimeter on the left is manual-ranging, with many different options (indicated by metric prefixes) for measuring different amounts of voltage, current, and resistance. The multimeter on the right is auto-ranging (note how it has fewer options for the selection knob), meaning it will automatically select the appropriate range.

What do the other symbols on the multimeter mean?

You might have noticed some other symbols besides V, A, Ω, and metric prefixes on the front of your multimeter. We'll explain some of those symbols here, but remember, all multimeters are different, so we cannot cover every possible option in this tutorial. Check your multimeter's manual if you still can't figure out what one of the symbols means. You can also browse our multimeter gallery to see labeled pictures of different multimeters.

Multimeter Symbol	Samples
~ (squiggly line): You might see a squiggly line next to or above a V or A on the front of your multimeter, in addition to metric prefixes. This stands for alternating current (AC). Note that the voltage in an AC circuit is usually referred to as "AC voltage" (even though it sounds strange to say "alternating current voltage"). You use these settings when you are measuring a circuit with alternating current (or voltage).
—, - - - (solid line or dashed line): Like the squiggly line, you might see this next to or above a V or an A. The straight lines stand for direct current. You use these settings when you are measuring a circuit with direct current (e.g., most circuits that are powered by a battery).
DCV, ACV, ACA, DCA, VAC, or VDC: Sometimes, instead of (or in addition to) using squiggly or dashed lines, multimeters will use the abbreviations AC and DC, which stand for alternating current and direct current, respectively. Note that some multimeters might have AC and DC after the V and A, instead of before.
Continuity check (series of parallel arcs): This is a setting used to check if two things are electrically connected. The multimeter will beep if there is a conductive path between the two probe tips (meaning, if the resistance is very close to zero), and will not make any noise if there is no conductive path. Note that sometimes the continuity check can be combined with other functions on a single setting.
Diode check (triangle with some lines through it): This function is used to test a diode, which is like a one-way valve for electricity; it only lets current flow in one direction. The exact function of the diode check can be different on different multimeters. Check your multimeter's manual to learn about how the diode check function works for your model.

Table 1. Some symbol examples from different multimeters. Check out the gallery for more examples.

What are the red and black wires (probes)? Where do I plug them in?

Your multimeter probably came with red and black wires that look something like the ones in Figure 4. These wires are called probes or leads (pronounced "leeds"). One end of the lead is called a banana jack; this end plugs into your multimeter (Note: some multimeters have pin jacks, which are smaller than banana jacks; if you need to buy replacement probes, be sure to check your multimeter's manual to find out which kind you need). The other end is called the probe tip; this is the end you use to test your circuit. Following standard electronics convention, the red probe is used for positive, and the black probe is used for negative.

Figure 4. A typical pair of multimeter probes.

Although they come with two probes, many multimeters have more than two places in which to plug the probes, which can cause some confusion. Exactly where you plug the probes in will depend on what you want to measure (voltage, current, resistance, continuity test, or diode test) and the type of multimeter you have. We have provided one example in the images below—and you can check our gallery for a multimeter similar to yours—but since all multimeters are slightly different, you might need to consult the manual for your multimeter.

Most multimeters (except for very inexpensive ones) have fuses to protect them from too much current. Fuses "burn out" if too much current flows through them; this stops electricity from flowing, and prevents damage to the rest of the multimeter. Some multimeters have different fuses, depending on whether you will be measuring high or low current, which determines where you plug the probes in. For example, the multimeter shown in Figure 5 has one fuse for 10 amps (10A) and one fuse for 200 milliamps (200mA).

Figure 5. This multimeter has three different ports labeled 10A, COM (which stands for "common"), and mAVΩ. The fuse between mAVΩ and COM is rated for 200mA, which is a relatively "low" current. So, in order to measure small currents-or voltage or resistance (very little current flows through the multimeter when measuring voltage or resistance)—you plug the black probe into COM and the red probe into the port labeled mAVΩ. The fuse between 10A and COM is rated for 10A, so to measure high currents, you plug the black probe into COM and the red probe into the port labeled 10A.

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