Multimeter Trivia Questions & FAQ

A multimeter or a multitester, also known as a volt/ohm meter or VOM, is an electronic measuring instrument that combines several measurement functions in one unit. A typical multimeter may include features such as the ability to measure voltage, current and resistance. Multimeters may use analog or digital circuits?analog multimeters and digital multimeters (often abbreviated DMM or DVOM.) Analog instruments are usually based on a micro ammeter whose pointer moves over a scale calibration for all the different measurements that can be made; digital instruments usually display digits, but may display a bar of a length proportional to the quantity measured.

Multimeter can be a hand-held device useful for basic fault finding and field service work or a bench instrument which can measure to a very high degree of accuracy. They can be used to troubleshoot electrical problems in a wide array of industrial and household devices such as electronic equipment, motor controls, domestic appliances, power supplies, and wiring systems.

Voltage, alternating and direct, in volts. Current, alternating and direct, in amperes. The frequency range for which AC measurements are accurate must be specified. Resistance in ohms. Additionally, some multimeters measure: Capacitance in farads. Conductance in siemens.Decibels. Duty cycle as a percentage.

The resolution of a multimeter is often specified in "digits" of resolution. For example, the term 5? digit refers to the number of digits displayed on the display of a multimeter. By convention, a half digit can display either a zero or a one, while a three-quarters digit can display a numeral higher than a one but not nine. Commonly, a three-quarters digit refers to a maximum value of 3 or 5. The fractional digit is always the most significant digit in the displayed value. A 5? digit multimeter would have five full digits that display values from 0 to 9 and one half digits that could only display 0 or 1. Such a meter could show positive or negative values from 0 to 199,999. A 3? digit meter can display a quantity from 0 to 3,999 or 5,999, depending on the manufacturer.

Accuracy figures need to be interpreted with care. The accuracy of an analog instrument usually refers to full-scale deflection; a measurement of 10V on the 100V scale of a 3% meter is subject to an error of 3V, 30% of the reading. Digital meters usually specify accuracy as a percentage of reading plus a percentage of full-scale value, sometimes expressed in counts rather than percentage terms.

Any ammeter, including a multimeter in a current range, has a certain resistance. Most multimeters inherently measure voltage, and pass a current to be measured through a shunt resistance, measuring the voltage developed across it. The voltage drop is known as the burden voltage, specified in volts per ampere.

A multimeter can utilize a variety of test probes to connect to the circuit or device under test. Crocodile clips, retractable hook clips, and pointed probes are the three most common attachments. Tweezers probes are used for closely-spaced test points, as in surface-mount devices. The connectors are attached to flexible, thickly-insulated leads that are terminated with connectors appropriate for the meter. Probes are connected to portable meters typically by shrouded or recessed banana jacks, while bench top meters may use banana jacks or BNC connectors. 2mm plugs and binding posts have also been used at times, but are less common today.

A general-purpose DMM is generally considered adequate for measurements at signal levels greater than one mill volt or one mill ampere, or below about 100 megohms?levels far from the theoretical limits of sensitivity.

One important measurement that can be made with a multimeter is a resistance measurement. Not only can these be made to check the accuracy of a resistor, or check it is functioning correctly, but resistance measurements can be required in many other scenarios as well. It may be to measure the resistance of an unknown conductor, or it may be to check for short circuits and open circuits. In fact there are many instances where measuring resistance is of great interest and importance. In all these cases a multimeter is an ideal piece of test equipment for measuring resistance.

Additional scales such as decibels, and functions such as capacitance, transistor gain, frequency, duty cycle, display hold, and buzzers which sound when the measured resistance is small have been included on many multimeters. While multimeters may be supplemented by more specialized equipment in a technician's toolkit, some modern multimeters include even more additional functions for specialized applications.