Multimeters

Multimeters are measuring devices which combine several functions in one device as they are used to measure electrical voltage, current, frequency and resistance. The basic instruments that make up a multimeter are an ammeter, voltmeter and ohmmeter. While current, voltage, and resistance measurements are considered to be standard features of a multimeter, newer models are designed to measure many other quantities. Some common additional measured quantities and the units in which they are measured: Inductance in Henrys, capacitance in Farads, conductivity in Siemens, temperature in Celsius and Fahrenheit, frequency in Hertz and duty cycle as a percentage.

Mutimeters are very useful in all industrial settings as measuring attributes of an electrical current is very important in troubleshooting, maintenance and design of electrical circuits. However, because modern appliances and systems are now more complicated, multimeters aren’t used as often as more advanced and specialized instruments are replacing them. For instance, somebody who may have used an ohmmeter to measure resistance while testing an antenna may now use a hand-held analyzer to test several parameters in order to determine the integrity of a network cable.

A multimeter has either a spring-loaded clamp or a probe for sensors. The clamp is passed around the current carrying cable and its suitable buttons; allowing you to set the range for which the measurement is to be done. Multimeters come in either bench or hand-held types and they are usually powered by a set of batteries. Hand held multi meters are ideal for basic fault finding and field service work. Multimeters also come with an overload specification and can have temperature compensation.

These meters can be either analog or digital in design. With the analog meters, the pointer moves along a mirror-graduated dial. With digital meters, the reading can be directly read in units. Analog multimeters are not always accurate because of errors introduced in zeroing and reading the analog meter face. Analog meters may be implemented with vacuum tubes to precondition and amplify the input signal. These types of meters are known as vacuum tube volt meters (VTVM) or vacuum tube multimeters (VTMM).

Most modern multimeters are exclusively the digital type and are identified by the term DMM for digital multimeter. The signal being tested in a digital multimeter is converted to a digital voltage. Since the digital display will directly indicate a quantity as a number, there is no chance of parallax causing an error when viewing the reading.

Better circuitry and electronics have improved multimeter accuracy. Older analog meters might have basic accuracies of five to ten percent. Modern portable DMMs may have accuracies of 0.025%, and bench-top meters have accuracies in the single-digit parts per million figures. The inclusion of solid state electronics such as control circuits to small embedded computers has enabled a number of convenience features in modern digital meters.

Modern meters may be interfaced with personal computers. The interface allows the computer to record the measurements as they are taken or for the instrument to upload the results to the computer.


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