Electricity: Multimeter

Follow along this post to master the three most basic functions of a multimeter: Testing continuity, voltage and resistance.

Testing continuity

• A continuity test tells us whether two things are electrically connected: if something is continuous, an electric current can flow freely from one end to the other.
• If there’s no continuity, it means there is a break somewhere in the circuit. This could indicate anything from a blown fuse or bad solder joint to an incorrectly wired circuit.
• Continuity is one of the most useful tests for electronics repair.

Step 1

To begin, make sure no current is running through the circuit or component you want to test. Switch it off, unplug it from the wall, and remove any batteries.

• Plug the black probe into the COM port on your multimeter.
• Plug the red probe into the VΩmA port.

Step 2

• Switch on your multimeter, and set the dial to continuity mode (indicated by an icon that looks like a sound wave).

Step 3

• The multimeter tests continuity by sending a little current through one probe, and checking whether the other probe receives it.

• If the probes are connected—either by a continuous circuit, or by touching each other directly—the test current flows through. The screen displays a value of zero (or near zero), and the multimeter beeps. Continuity!

• If the test current isn’t detected, it means there’s no continuity. The screen will display 1 or OL (open loop).

Testing Direct Current voltage

• Plug the black probe into the COM port on your multimeter.
• Plug the red probe into the VΩmA port.

• Switch on your multimeter, and set the dial to DC voltage mode (indicated by a V with a straight line, or the symbol ⎓).

• Most multimeters are not autoranging, meaning you will need to set the correct range for the voltage you expect to measure.
  • Each setting on the dial lists the maximum voltage it can measure. So for example, if you expect to measure more than 2 volts but less than 20, use the 20 volt setting.
  • If you’re not sure, start with the highest setting.

Step 1

Place the red probe on the positive terminal, and the black probe on the negative terminal.

• If your range was set too high, you may not get a very accurate reading. Here the multimeter reads 9 volts. That’s fine, but we can turn the dial to a lower range to get a better reading.

• If you set the range too low, the multimeter simply reads 1 or OL, indicating that it is overloaded or out of range. This won’t hurt the multimeter, but we need to set the dial to a higher range.

Step 3

• With the range set correctly, we get a reading of 9.42 volts.

• Reversing the probes won’t do any harm; it just gives us a negative reading.

Testing resistance

• Plug the black probe into the COM port on your multimeter.
• Plug the red probe into the VΩmA port.

Step 1

• Switch on your multimeter, and set the dial to resistance mode.
• Resistance is measured in ohms, indicated by the Ω symbol.
• Most multimeters are not autoranging, meaning you will need to set the correct range for the resistance you expect to measure. If you’re not sure, start with the highest setting.

Step 1

• Place one probe at each end of the circuit or component you want to test.
• It doesn’t matter which probe goes where; resistance is non-directional.

• If your multimeter reads close to zero, the range is set too high for a good measurement. Turn the dial to a lower setting.

• If you set the range too low, the multimeter simply reads 1 or OL, indicating that it is overloaded or out of range. This won’t hurt the multimeter, but we need to set the dial to a higher range.

Step 2

• With the multimeter set to a usable range, we get a reading of 1.04k ohms.