Multimeter Symbol Guide
When you need a multimeter for testing electrical equipment around the home, it's vital to know what all those symbols around the dial mean.
Back in the early days of electricity, lab workers could measure electric current in a circuit using an ammeter (galvanometer) and voltage using a voltmeter. From there, they could calculate resistance.
In 1920, British postal engineer Donald Macadie invented the AVOmeter, which measured all three quantities (A = amps, V = volts, O = ohms). Soon after, electricians working in the field got their hands on somewhat portable versions of this invention.
Today’s multimeters do the same jobs as the AVOmeter, but they’re more sophisticated and can do multiple other tests as well. Depending on the model, a multimeter can tell you whether a diode or capacitor is working, distinguish between alternating and direct current and measure wire temperature. Functions are denoted by symbols arranged around a dial.
Homeowners doing DIY electrical work don’t need the same functionality as electronics technicians, so multimeters sold in hardware stores are less complicated than those at electronics supply outlets. Even so, the symbols can be difficult to decipher. Here’s a rundown of the electrical terms and symbols you’ll find on a basic multimeter for home use and what they mean.
Multimeter Symbols You Need to Know
Multimeters can measure direct current (DC) voltage and alternating current (AC) voltage, so they need to display more than one voltage symbol. On some older models, the designation for AC voltage is VAC. These days, it’s more common for manufacturers to place a wavy line over the V to signify AC voltage.
To signify DC voltage, the convention is to place a dotted line with a solid line above it over the V. To get voltage readings in millivolts (one-thousandth of a volt), set the dial to mV.
- “V” with a wavy line over it = AC voltage.
- “V” with one dotted and one solid over it = DC voltage.
- “mV” with one wavy line or a pair of lines, one dotted and one solid, over it = AC or DC millivolts.
Like voltage, current can be AC or DC. Because the unit for current is ampères, or amps, the symbol for it is A.
- “A” with a wavy line over it = AC current.
- “A” with two lines, one dotted and one solid, over it = DC current.
- mA = Milliamps.
- µA (µ is the Greek letter mu) = Microamps (millionths of an amp).
A multimeter measures resistance by sending a small electric current through the circuit. The symbol for the unit of resistance, the ohm, is the Greek letter omega (Ω). Meters don’t distinguish between AC and DC resistance, so there are no lines above this symbol.
On meters with range selection options, you can select the kilohm (1,000 ohms) scale and the mega ohm (one million ohms) scale, which are kΩ and MΩ, respectively.
- Ω = Ohms.
- kΩ = Kilohms.
- MΩ = Mega ohms.
Use a multimeter to test for a break in an electrical circuit. The meter measures resistance, and there are only two outcomes. Either the circuit is broken (open), in which case the meter reads infinite resistance (denoted on digital meter displays as OL for open line), or the circuit is intact (closed), in which case the meter reads 0 (or close to it).
Because there are only two possibilities, some meters beep when they detect continuity. This function is denoted on the dial settings by a series of left-facing brackets of increasing size, like a sideways version of the wireless reception symbol on a laptop.
Diode and Capacitance Tests
Electronics technicians are more likely to use the diode and capacitance tests than electricians or homeowners. But if you have a meter with these functions, it helps to know what the symbols mean.
The diode test function looks like an arrow pointing toward the center of a plus sign. When this function is selected, the meter will tell you whether a diode (a common electronics component that changes AC current into DC current) is working or not.
The capacitance function resembles a right-facing bracket to the right of a vertical line. Both are crossed by a horizontal line. Capacitors are electronic devices that store charge, and the meter can measure the charge.
The temperature function measures the temperature of the circuit wires. It’s denoted by a thermometer.
Jacks and Buttons
Two leads are supplied with every multimeter, one black and one red. Some meters have three jacks and some four. The jacks into which you plug the leads depend on what you’re testing.
- COM is the common jack, and it’s the only black one. You always plug the black lead into this jack.
- A is the jack where the red lead goes if you’re measuring high current up to 10 amps.
- mAVΩ is the jack for every other measurement, including sensitive current measurements, voltage, resistance and temperature, if the meter has only three jacks.
- mAµA is the jack for sensitive current measurements (less than one amp) if the meter has four jacks.
- VΩ is the jack for all other measurements except current.
At the top of the meter display, above the dial, you usually find two buttons, one to the left and one to the right.
- Shift. To save space, manufacturers may assign two functions to some dial positions. You access the function marked in yellow by pressing the shift button, which is usually also yellow and may or may not be marked.
- Hold. Pressing this button freezes the current reading for later reference.
Manual vs. Auto Range
An older analog multimeter with a needle needs to have more than one range setting. If the meter had only a large range, it couldn’t be used for sensitive measurements because the needle would hardly deflect. On the other hand, if the meter had only a small range, any measurement exceeding that range, no matter what it was, would deflect the needle to its maximum.
Digital multimeters with LED displays were introduced in the 1970s, and today most multimeters are digital. Some still have range settings that you select with a dial. But increasingly, the meter selects the range automatically.
Because these multimeters don’t have range settings (which can occupy up to 18 dial positions), auto-range multimeters can have more functionality than those with manual range settings.
Note: Retain the owner’s manual of your multimeter for reference. Keep the manual and the multimeter clean and dry in a quart- or gallon-size plastic zip-top freezer storage bag.