A digital multimeter is a tool that can measure amps, volts, and ohms. It is different from an analog meter, which has a needle and a gauge, in that it has a digital light-emitting diode (LED) display. Digital multimeters are typically more accurate than their old analog counterparts. A digital multimeter can also have other functions; obviously, the more expensive meters will have more features, but all of them measure the three basic currents.
A digital multimeter, or DMM, can be extremely helpful when trying to resolve an electrical problem. DMM’s are used all the time in the automotive industry, construction, machine repair, the computer industry, and any other field that involves any sort of electrical work. When purchasing a digital multimeter, the most important specification to look for is its operating resistance, also called impedance. The DMM becomes part of the circuit being tested, thus it affects the current in that circuit.
Another specification to consider when purchasing a DMM is its range. Regardless of what current is being tested, the proper range for that measurement is critical to the accuracy of the measurement. If the operator were testing a 12-volt battery, for instance, then a range setting of 0 to 25 volts would result in a more accurate measurement then a range setting of 0 to 500 volts. Thankfully, many DMM’s have an automatic range feature, which will set the proper range for the circuit being tested automatically; all the operator has to do is set the DMM to the proper current being tested, and the meter does the rest.
When using a DMM for the first time, it is essential that a person read the instruction manual that comes with it. Many DMM’s require different steps for taking measurements; this will entail pressing certain buttons before hooking up the leads, and so on. Most digital multimeters require a battery for operation. The instruction manual will most likely specify which type of battery to use. If the battery type is not specified, alkaline batteries are typically used.
A DMM’s maximum reading capacity is extremely important as well. This is the maximum amount of current that the meter can measure. Usually, the current limit is printed on the face of the DMM. A common limit is 10 amps. This means that if the meter is hooked up to a current of 12 amps, the internal fuse will pop to prevent damaging the meter. Installing a bigger fuse will not increase the limit of the DMM; it will only burn it out permanently.
Whether testing a battery, measuring a circuit’s capacity, or trying to pinpoint an electrical short, a digital multimeter is a versatile little device that is a staple of any toolbox.