How To Use a Multimeter
As the name suggests, a multimeter can be used to record multiple types of measurements. A multimeter can be used for circuit diagnosis, battery testing, AC and DC voltage testing, troubleshooting, measuring resistance, and more. Here, we will cover the basics of using a multimeter as well as some of the more commonly used functions. While not all multimeters are exactly the same, they are relatively simple devices and the information in this How To should apply to almost all models.
Every multimeter has three basic parts: a display, a selector knob, and input jacks for test probes (or leads).
- The display will have a digital readout, usually showing four digits, with room at the sides, top, and bottom for additional, smaller display functions. Or, the display may be analog, with an arc-shaped dial and moving pointer.
- The selector knob allows users to set the function/reading of the multimeter; usually volts, ohms, and amps, with a range of scales for each (x1, x10, x100, etc.). A typical line of settings might read: 200mV – 2V – 20V – 200V.
- AC or DC voltage can be measured with a multimeter. “V—“ indicates DC voltage settings; “V~” indicates AC settings.
- Two probes can be plugged into the input jacks—most multimeters have more than two jacks, but only two should ever be used at once.
- One jack will be labeled “COM” (common), which connects to the ground or “-“ of a circuit; this uses the black cable.
- Other jacks will connect to the “+” of a circuit, using the red cable. They may have a number of labels, including “V” (for measuring volts), “A” and/or “mA” (for measuring amps/milliamps/current), “Ω” (for measuring ohms/resistance), or “mAVΩ” (for measuring current, voltage, or resistance through a single input).
- Make sure you use the correct jack for what you are measuring, to avoid damage to the multimeter and possible injury.
Testing Circuit Voltage with A Multimeter
- Plug your + lead into the “V” input.
- Set the selector knob to AC or DC voltage, as needed.
- Touch the red probe to the positive terminal of the device being tested, and the black probe to the negative terminal.
- You should now have a voltage reading on your display. If the probes are reversed, you will see the reading as negative voltage; this is fine—it will not damage the multimeter or the circuit.
- If the circuit voltage is too high or too low for the selected range, a digital display will show an error message of some kind; analog displays will peg to the right if it’s too high, and will simply not register if it’s too low. Adjust the range on the selector dial up or down as needed.
- Almost any circuit can be tested this way. Be careful not to short anything out with the metal probes.
Testing Circuit Continuity with A Multimeter
- Plug your + lead into the “Ω” input.
- Set the selector knob to the continuity setting, usually indicated by a “speaker” or “volume” icon one might see at the bottom left of a YouTube video (to the right of Play/Pause).
- Touch the probes to any two points in the circuit (probe color doesn’t matter here). If there is a good, working connection between the two points, the multimeter will beep.
- If the multimeter does not beep, the circuit is bad.
Testing A Battery with A Multimeter
- Plug your + lead into the “V” input.
- Set the selector knob to DC voltage (all batteries produce DC voltage). Adjust the range accordingly to cover the maximum power rating of the battery. This may require some trial and error (see Step 5 of Testing Circuit Voltage above).
- Touch the red probe to the positive terminal of the battery, and the black probe to the negative terminal.
- Your display should now give you a clear reading. If the probes are reversed, the display will show negative voltage; this will not damage the multimeter or the battery.
- All types of batteries can be tested in this manner.
Testing An Electrical Outlet with A Multimeter
- Plug your + lead into the “V” input jack.
- Set the selector knob to AC voltage and adjust the range accordingly (120 to 240V for American power outlets; 240 to 380V for outlets in most other countries).
- Insert the black probe into one of the outlet’s straight slots. It should be held in place between the sides of the slot. For safety purposes, let go of the probe and allow it to stay in place on its own.
- Insert the red probe into the other straight slot.
- The display should indicate voltage close to the expected voltage (see Step 2).