Measuring Voltage With Multimeter

Using a Multimeter: Chapter 7

In this module, we will teach you how to use a multimeter to measure AC and DC voltage. Skip to quiz!

1. Settings

Let’s start by getting your multimeter ready to measure voltage. To measure voltage, you will need to plug your leads into the correct ports on your multimeter.

For measuring voltage, your red lead plugs into the port marked with the "V” symbol. This is the symbol for voltage. Our black lead will be plugged into the port marked with “COM”.

Recall that there are two types of current: direct current (DC) and alternating current (AC). With DC, the current flows in one direction. With AC, the current will periodically alternate the direction it flows in.

AC and DC current also produce a unique voltage. Voltage coming from an AC system is called AC voltage. Voltage coming from a DC system is called DC voltage.

Before taking any measurements, you need to set your multimeter dial to AC or DC voltage. Your multimeter will have two voltage symbols around the dial. One “V” symbol is for AC voltage. The other “V” symbol is for DC voltage.

The AC voltage symbol will be a “V” with a “∿” over the V. The DC voltage symbol will be a “V” with a solid and dashed line over the V. Rotate your dial until it points to the correct symbol.

Recall each dial position on a multimeter can have multiple measurements. It is common for AC and DC voltage to be on the same dial position. If they are on the same dial position, you will need to use the “function” key to switch between AC or DC voltage.

For example, you want to measure AC voltage. You would rotate the dial on your meter until it points to the “V” sign. See the picture to the right for an example. Then, you would press the function key until “AC” and “V” are displayed on the screen.

2. How to measure voltage using a multimeter?

Now that you know how to set your meter to voltage, let’s do through the process of measuring voltage.

Start by confirming that your black lead is plugged into the “COM” port and your red lead is plugged into the port marked “V”. Determine if the system runs on AC or DC power. Usually, you can find this information on the schematic. Set your multimeter dial to measure AC or DC voltage.

When measuring voltage, you will place your leads in parallel with the component. Recall that in parallel means that there are multiple paths for current to flow through a circuit. Parallel components will have reduced current, but the same voltage as each other.

To place your leads in parallel, you do not need to disconnect the circuit. You will place the tip of one lead on the entrance and the exit of the component. This places your meter in parallel with the component.

When you are measuring DC voltage, the placement of your leads effects the measurement. Since current flows in one direction in a DC circuit, each component has a positive and a negative end. For some components, the positive end will be marked in red. The negative end will be marked in black.

Place your leads on the positive and negative terminals of the component you are measuring. The red lead should be touching the positive end. The black lead should be touching the negative end.

If your multimeter reads a negative voltage, it means that your leads are in the wrong position. To fix this, reverse the order of your leads. Your black lead should go where your red lead is. Your red lead should go where your black lead is.

For example, let's say that you wanted to measure the voltage across a 12V DC battery. You would place your red lead onto the terminal marked with a “+” sign. The black lead will go on the terminal with a “-” sign. The voltage will appear on the multimeter display. For example, 12V.

Recall that AC current alternates direction. Because the current changes direction, there is no positive or negative side of components like in DC voltage. Your multimeter will not display a negative voltage while reading AC voltage.

Just like DC voltage, you need to place your leads in parallel with the component. Since there is no positive or negative terminals, you can place your leads on either terminal of the component. The voltage and units will appear on your multimeter display. For example, 5V.

Recall that some multimeters require you to manually set the range of your measurement. If your multimeter is not auto ranging, you will need to change the range to get a more accurate measurement. Slowly turn the dial to lower ranges until you get an accurate measurement.

3. Conclusion

In this section, you learned how to use your multimeter to measure AC and DC voltage. In the next section, we will teach you how to measure temperature.

Question #1: "V" is the universal symbol for voltage on a multimeter.

1. True

2. False

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Answer: True

True, the “V” symbol always represents voltage on a multimeter. This includes the dial and port.

Question #2: The “V” symbol with a “〜” above the V stands for DC voltage.

1. True

2. False

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Answer: False

False, the “V” symbol with a wave above the V stands for AC voltage.

Question #3: When you are measuring voltage, your black lead should plug into which port on your multimeter?

1. A

2. COM

3. V

4. Ω

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Answer: COM

Your black lead will always be plugged into the COM port when you are measuring voltage.

Question #4: When measuring voltage, you must place your leads in ____ with the circuit.

1. Parallel

2. Series

3. Rotation

4. Linear

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Answer: Parallel

When measuring voltage, your leads must be connected in parallel.

Question #5: Every component with a DC power supply will have a positive and a negative terminal.

1. True

2. False

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Answer: True

True, the current only flows in one direction with DC current. Since the current flows in one direction, each component has a positive and negative end.

Question #6: A negative DC voltage reading means that:

1. Your multimeter is broken

2. You must reverse your lead placement

3. You are on the wrong setting

4. The range is too high for your meter.

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Answer: You must reverse your lead placement

A negative voltage reading means that your lead placement needs to be reversed.

Question #7: When you measure AC voltage, there is no positive and negative side of the component.

1. True

2. False

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Answer: True

True, with AC voltage the current alternates directions. This makes it impossible to have a positive or negative side.