A multimeter measures electrical properties such as AC or DC voltage, current, and resistance. Rather than have separate meters, this device combines a voltmeter, an ammeter, and an ohmmeter. Electricians and the general public might use it on batteries, components, switches, power sources, and motors to diagnose electrical malfunctions and narrow down their cause.
The two main kinds of a multimeter are analog and digital. A digital device has an LCD screen that gives a straight forward decimal read out, while an analog display moves a bar through a scale of numbers and must be interpreted. Either type will work over a specific range for each measurement, and users should select one that's compatible with what he or she meters most, from low-voltage power sources to high-voltage car batteries. Multimeters are specified with a sensitivity range, so consumers should make sure they get the appropriate one.
As a voltmeter, the tool can measure the amount of AC or DC voltage flowing through a circuit. Voltage is a difference in potential energy between the two points. A fan, for example, should be drawing 120 volts (in the U.S.) from the plug in the wall, but a computer scanner might only draw 12 volts from a converter. To test these components, the user should choose AC or DC, select an upper limit on the voltage, and plug the machine in question right into the multimeter, without breaking the circuit. The readout should reveal whether the device is functioning normally, when compared to the data specified in the user's manual.
As an ohmmeter, it finds the resistance in a circuit, which is given in ohms. A user can find the resistance at any point in a circuit by first unplugging the machine from a wall outlet or battery source then putting in an approximate range he or she expects to contain the number of ohms. The measuring tool actually passes a small amount of electricity from its own battery through the circuit to measure resistance by comparing the voltage sent out to what it receives.
When used as an ammeter, the multimeter measures current flowing through a closed circuit by interrupting that circuit. The tool can only be connected in series, which means that all the circuit's current will flow through the ammeter's sensors. The user will still need to select the range in which he or she expects the current to fall. This feature is used less often than the others, so some multimeters do not measure current at all.