Multimeter Symbols Meaning
When you need to test electrical equipment around the house with a multimeter, it's important to know what all the symbols around the dial mean.
In the early days of electricity, lab workers used an ammeter (galvanometer) and a voltmeter to measure the amount of electricity in a circuit. From there, they could calculate resistance.
In 1920, British postal engineer Donald Macadie made the AVOmeter, which could measure all three quantities (A = amps, V = volts, O = ohms). Soon after, electricians who worked in the field were able to get their hands on versions of this invention that were more portable.
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 if a diode or capacitor is working, tell the difference between direct and alternating current, and measure the temperature of a wire. Symbols around a dial show what functions it has.
Homeowners who do their own electrical work don't need the same features as electronics technicians, so multimeters sold at hardware stores are simpler than those sold at stores that sell supplies for electronics technicians. Even so, figuring out what the symbols mean can be hard. Here is a list of the electrical terms and symbols you'll find on a basic multimeter for home use and what they mean.
Symbols on a Multimeter
Since multimeters can measure both direct current (DC) and alternating current (AC), they need to show more than one symbol for voltage. On some older devices, the word VAC stands for AC voltage. AC voltage is usually shown on products these days by putting a wavy line over the V.
As a rule, a dotted line with a solid line above it is drawn over the V to show DC voltage. Set the dial to mV to read voltage in millivolts, which is one-thousandth of a volt.
Current can be either AC or DC, like voltage. Since amps are the unit for current, the symbol for it is A.
Sending a small amount of electricity through the circuit is how a multimeter measures resistance. The Greek letter omega (Ω) stands for the ohm, which is a unit of resistance. There are no lines above this symbol because meters can't tell the difference between AC and DC resistance.
On meters that let you choose the range, you can choose between the kilohm scale (1,000 ohms) and the mega ohm scale (one million ohms), which are written as kΩ and MΩ, respectively.
Use a multimeter to check if an electric circuit is broken. There are only two possible results when the meter is used to measure resistance. Either the circuit is broken (open), in which case the meter reads "infinite resistance," or the circuit is complete (closed), in which case the meter reads "0."
Some meters beep when they find continuity because there are only two options. On the dial settings, this function is shown by a series of left-facing brackets that get bigger, like the wireless reception symbol on a laptop turned sideways.
Diode and Capacitance Tests
Diode and capacitance tests are more likely to be used by electronics techs than by electricians or homeowners. But if you have a meter that can do these things, you should know what the symbols mean.
The diode test function looks like a plus sign with an arrow pointing toward the middle. When this function is turned on, the meter will tell you if a diode is working or not. A diode is a common electronic part that turns AC current into DC current.
The capacitance function looks like a right-facing bracket to the right of a vertical line. A horizontal line goes through both. Capacitors are electronic devices that store charge, and the meter can measure that charge.
The temperature function checks how hot or cold the wires are. A thermometer shows what it is.
Jacks and Buttons
Every multimeter comes with two leads, one black, and one red. There are three and four jacks on some meters. Depending on what you're testing, you plug the leads into different jacks.
Most meters have two buttons, one to the left and one to the right, at the top of the screen, above the dial.
Manual vs. Auto Range
An old analog multimeter with a needle needs to have more than one range setting. If the meter only had a large range, the needle wouldn't move much, so it couldn't be used for sensitive measurements. On the other hand, if the meter had a small range, any measurement that was outside of that range, no matter what it was, would move the needle to its maximum.
In the 1970s, LED displays were added to digital multimeters. Today, most multimeters are digital. Some still have a dial that lets you choose the range setting. But more and more, the range is chosen automatically by the meter.
Auto-range multimeters can be more useful than those with manual range settings because they don't have range settings, which can take up to 18 dial positions.
Note: Keep the owner's manual for your multimeter in case you need to look it up. Put the manual and the multimeter in a quart- or gallon-size plastic bag with a zip-top to keep them clean and dry.