Beginner’s Guide to Multimeters: Parts, Use, and Reading

A multimeter function as an electrical tester and is a crucial instrument for diagnosing a broad spectrum of electrical components. Its potential applications are diverse, but it is commonly utilized to assess the functionality of wires, power cords, and batteries. Additionally, this device is employed to examine power outlets for functionality.

Multimeters are categorized into two types – analog and digital – distinguished primarily by their display method. Analog multimeters exhibit measurements through a moving needle across a graduated scale, whereas digital multimeters feature an LCD screen showcasing measurements in either four or five digits.

Further insights into the operation of a multimeter can be found in the subsequent step-by-step instructions.

What Is a Multimeter?

A multimeter is a measurement device used to measure multiple electrical values. Multimeters can measure voltage, current, resistance, and (sometimes) test for continuity. Analog multimeters don’t usually offer a continuity function, though some do.

What Do Multimeters Measure?

The multimeter’s impressive versatility is owed to its ability to test for the three basic units of electricity, including:

• Voltage: Multimeters can test two forms of voltage: alternate current (AC) and direct current (DC). AC is the voltage used in your home’s electrical wiring, while DC is used primarily in batteries used in vehicles, residential solar systems, and consumer electronics. Voltage is measured in volts.
• Resistance: Resistance is the opposition to the flow of current through a circuit and is measured in ohms.
• Current: Generally speaking, current is the amount of electricity flowing through the circuit and is measured in amps. The number of amps flowing through a circuit is the difference between the voltage applied and the resistance present. Milliamps (1/1,000 of an amp) are the most common unit of amps measured with a multimeter.

In addition to testing those three functions, some multimeters test for continuity, or the absence of resistance within a circuit. Not all multimeters have dedicated continuity functions, but those that do emit an audible beep when continuity is present. If this setting isn’t present, testing the resistance can be used instead.

Parts of a Multimeter

• Display: The window where the electrical measurements are displayed.
• Selection Knob Label: This round dial allows you to select what you want to measure, such as the type of electrical unit or continuity.
• Selecting Type of Unit to Measure: Move the dial on the selection knob to select the type of electrical unit to measure. You can switch between AC volts (may look like a V with a squiggly line on either side or above it), DC volts (may look like DC-), resistance (Ω), amps (A), and milliamps (mA).
• Selecting Continuity: Move the dial on the selection knob to select continuity. Continuity is marked with a diode symbol (triangle with a line on the right side) and/or a soundwave symbol. (Not every multimeter has this selection.)
• Probes: Red and black wires are used to physically test the electrical component. Each one is equipped with a pointy metal tip on one end, and a banana plug (a prong surrounded by a protective tube) on the other. The metal tip is used to probe the component being tested, and the banana plug connects to one of the multimeter’s ports. While there’s no actual difference between the two probes, the black cord is often used to test ground and neutral (or common) terminals, and the red wire is normally used for hot terminals. When testing for resistance and continuity, it makes no difference which probe is used where.
• Ports: Most multimeters are equipped with three ports: COM (or “-”), mAVΩ, and 10A. COM stands for common and is what the black probe is usually plugged into. The mAVΩ port is where the red probe plugs into to measure volts, resistance, and current. The 10A port is a specialty port that’s used when measuring currents greater than 200 mA. Some multimeters have four ports that split the functions of the mAVΩ setting in two, with one VΩ setting for volts and resistance and a µAmA setting for current.
• Scales (Analog Only): There are AC or DC scales with a “V” to measure voltage. There are AC or DC scales without a “V” to measure current.
• Meter Pointer (Analog Only): There is a straight line, which is often red, that moves back and forth to read voltage, amps, or ohms.

Safety Considerations

When using a multimeter to test live electricity, it’s important to take certain safety precautions to avoid any chance of electrocution as accidents can occur.1 These include:

• Wearing insulated gloves
• Not using a multimeter with any broken or frayed wires on the probes
• Not performing any electrical testing in wet conditions
• Not touching the tips of the probes together while testing

WARNING

How to Use a Multimeter

1. Test Your Multimeter

It’s important to check the multimeter first to ensure its correct before beginning a project. Take the following steps:

• Turn the multimeter’s selection knob to ohms.
• Plug the black probe wire into the common port.
• Plug the red probe wire into the ohms jack.
• Tap the red and black probe tips together to ensure its reading less than or equal to 0.5 ohms.

2. Measure Volts

Turn the selection knob to either AC or DC volts, depending on what you’re testing. In general, you will place the black probe on the negative terminal of the component you’re testing, and the red probe on the positive terminal. Here are more specifics:

Checking AC voltage of an outlet: As an example, if you’re testing a standard, 3-pronged electrical outlet in a home in the United States, take these steps to measure volts:

• Turn the selection knob to AC volts and ensure the probes are plugged into the appropriate port.
• Place the black probe into the slot on the top left of the outlet (neutral) and the red probe into the upper right slot (hot).
• If the measurement doesn’t read around 120 volts, a wiring issue is likely to be blamed. Another indication of a wiring issue is if you place the black probe into the u-shaped slot on the bottom of the outlet (ground), the red prong into the neutral slot, and the measurement is greater than 0.
• Test the outlet’s ground by inserting the black prong into the bottom slot, and the red probe in the hot slot. The measurement should be roughly 120 volts, or else the outlet has a bad ground.

Checking DC voltage of a battery: As an example, if you’re testing a standard household battery, take these steps to measure volts:

• Disconnect the battery from its housing, such as from a tool, device, or charger.
• Turn the selector knob to V DC volts (or the “battery” section if you have one on your multimeter). Set the range for higher than the voltage of the battery you are checking. For example, if you are checking a 9-volt battery, set the dial to 20.
• Insert the black probe in the common jack.
• Plug the red plug into the jack labeled for DC voltage, VΩ, or V–.
• Place the black plug on the battery’s negative side.
• Place the red probe on the battery’s positive side.
• Note the reading to see if you need to replace a weak battery.
• Disconnect the red probe first and then the black probe when finished.

3. Check Continuity

A common use of continuity testing is checking the functionality of a power cord. Take these steps:

• Unplug the appliance before checking the cord for continuity.
• If your multimeter has a dedicated continuity setting, turn the selection knob to continuity.
• Verify the meter and probes are working by touching the tips of the probes together. The meter should beep if it’s working properly.
• Start by touching one of the multimeter probes to one of the prongs on the male side of the power cord.
• Insert the other probe into the corresponding slot on the female end of the cord. The multimeter will make an audible beep if there is continuity.
• Repeat this process on the remaining male prong and female slot. If there wasn’t a beep on either side, the power cord needs to be replaced.
• Next, touch one of the probes to one of the prongs on the male end of the cord, and the other probe to the other male prong on the same end.
• If the meter beeps, that indicates a short and the cord needs to be replaced.

An alternative way to test a power cord: If your multimeter doesn’t have a continuity setting, test the resistance of a power cord instead by taking these steps:

• Unplug the appliance before checking resistance.
• Turn the selection knob to the Ω (ohms) setting.
• Use the same procedure outlined above.
• Look for a reading between 0 and 1 on the display instead of listening for an audible beep.
• If the reading is 1 or OL (open loop), the circuit lacks continuity and the cord should be replaced.

4. Measure Resistance

Aside from testing continuity, measuring resistance is commonly used when checking an electrical component’s resistors (such as in a speaker).

If checking a resistor, you will determine the resistor’s resistance value. This can either be found marked on the resistor itself or in the owner’s manual of the component being tested. Take these steps:

• Turn the selection knob to the Ω (ohms) setting.
• Place each of the multimeter’s probes on one of the resistor’s leads.
• Read the resistance value. If the resistor is functioning properly, the resistance value on the meter’s display should be the same as the resistor’s rating. If not, the resistor is defective and needs to be replaced.

5. Measure Amps

You would measure amps with a multimeter to diagnose a vehicle’s electrical issues. For example, you would need a multimeter reading to know if there is a parasitic draw on the battery. Take these steps.