Multimeter use – voltage, continuity, resistance – and some tips

Multimeters are good for electrical basics – check current, measure voltage and troubleshooting for why your circuit’s not working, or if the switch is broken.

Here are some tips.
WARNING: To test continuity you should turn off the power to the system.

If you switch the red and black probes, the reading on the multimeter is simply negative. Nothing bad will happen to anything.

Understand that the multimeter is acting as a piece of wire – measuring or completing the circuit.

Electrical resistance is a measure of the difficulty to pass a current flow though a conductor. Electrical conductance is the ease that electricity passes.

Most multimeters need the correct range set for the resistance you expect to measure. If you’re not sure or the range, start with the highest setting.

To measure current in a series, you must place the red probe on the lead of a component and the black probe on the next component lead. The multimeter will be part your circuit. If you disconnect the multimeter, your circuit won’t work.

Remember: resistors can’t be in circuit when measured else you can get a false reading from the connected circuit interfering with the measurement.

COM means common and is almost always connected to ground or negative. The COM probe is usually black.

When there is little resistance between two points (a few ohms), the two points are electrically connected.

Batteries are direct current (DC). Almost all portable electronics use DC. Connect the black probe to the battery’s ground or negative (-) and the red probe to power or positive (+).

Brownouts are low voltage situations. Check the voltage before running large appliances, or you may burn-out the mechanics due to low voltage.

A battery may show voltage, but not have enough “bang” to open the garage door.