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A multitester or multimeter is also known as a VOM (volt-ohm-milliammeter), is an electronic measuring instrument that combines several measurement functions into one unit. A normal multimeter can measure resistance, voltage, and current. Analog multimeters use a microammeter with dynamic pointers to display readings. Digital multimeters (DMM, DVOM) have numerical displays, and can also show graphical bars representing the measured value. Digital multimeters have replaced analog multimeters because they are now cheaper, more precise, and more physically robust.
A multimeter can be a handheld device that is useful for field service work and basic fault detection or a bench instrument that can measure accuracy to a great extent. Multimeters are available in a variety of features and prices.
History of Multimeter
The first moving current detector was the galvanometer in 1820. This wheel was basically used to measure voltage and resistance using the Stone Bridge and by comparing unknown quantities with reference voltage or resistance. While useful in the lab, the instruments were extremely slow and impractical in the field. These galvanometers were large and delicate.
The galvanometer uses a moving coil of the meter that carries a pointer and rotates on the reins of the axis or tout band. The coil rotates in a permanent magnetic field and is blocked by fine spiral springs that carry current to the moving coil as well. It provides proportional measurement rather than mere detection and is to be separated from meter orientation. Instead of balancing the bridge, the values can be read directly on the instrument scale, making measurement faster and easier.
The multimeter was invented in the early 1920s when radio receivers and other electronic devices with vacuum tubes became more common. Donald Macadie, a British post office engineer responsible for inventing the first multimeter, said he was not satisfied with the need to carry many separate devices to maintain telecommunication circuits. Donald Macadie invented a device that could measure amperes, volts, and ohms, hence the name fiction meter. The meter included voltage and precision resistors, a dynamic coil meter, and switches and sockets for range selection.
General properties of multimeters
Any meter will load the circuit under test to some extent. For example, a multimeter that uses the movement of a moving coil with a full-scale deformation current of 50 microamps (A), which is the most commonly available sensitivity, There must be at least 50 µA draws from the circuit under test to reach the upper end of Its scale. This allows the high load circuit to be loaded so high that it can affect the circuit, thus helping to reduce readings. In the case of "ohms per volt" (O/V), the full displacement current can be expressed. Ohm per volt data is often called the "sensitivity" of the device. Thus a 50 µA motion meter will have a "sensitivity" of 20,000 O/V. "Per volt" refers to the fact that the circuit meter presented under the test will be 20,000 be multiplied by the total voltage in which the meter is set. For example, if the meter is set to the 300 V full-scale limit, the meter barrier will be 6 MO. 20,000 O/V is the best (highest) sensitivity available for ordinary analog multimeters, which lacks internal amplifiers. For meters that have internal amplifiers (VTVMs, FETVMs, etc.), the input impedance is determined by the amplifier circuit.
Pocket watch style meters were widely used in the 1920s. The metal case was usually associated with a negative connection, an arrangement that caused multiple electric shocks. The technical specifications of these devices were often crude, for example, the ones described have a resistance of only 33 O/V, a nonlinear scale, and no zero adjustments.
Operation of multimeters
A multimeter is a combination of AC voltmeter, DC voltmeter, ammeter, and ohmmeter. A non-extended analog multimeter connects one-meter movement, range resistors, and switches. VTVMs are increasing the analog meter and it has active circuitry.
For analog meter movement, DC voltage is measured by a series resistor connected between the meter motion and the test circuit. A switch (usually rotary) with the movement of the meter allows entering the maximum resistance for reading high voltage in series. The main full-scale defect of the movement produces a defect current, and the combination of series resistance and its own resistance to movement gives the full-scale voltage of the range. As an example, a meter motion which, with an internal resistance of 500 O ?, requires 1 mA for full-scale fluctuations, at a 10 V range of multimeters, of the 9,500 O series resistance.
Resolution of Multimeter
The resolution of a multimeter is the smallest part of the scale that can be displayed, depending on the scale. On some digital multimeters, it can be configured, high-resolution measurements take longer to complete. For example, a multimeter with a 1 mV resolution on a 10V scale can show a change in measurement in 1 mV increments.
Accurate accuracy is a measurement error compared to perfect measurement. The measurement error is relatively accurate compared to the instrument used to calibrate the multimeter. Most multimeter data sheets provide relative accuracy. To calculate the absolute accuracy of relative accuracy of the multimeter, add the absolute accuracy of the instrument used to measure the multimeter.
Accuracy of Multimeter
Digital multimeters usually measure with accuracy from their analog counterparts. Usually, standard analog multimeter measurements with ±3% accuracy, although high accuracy instruments are made. Standard portable digital multimeters typically range from ± 0.5 in the DC voltage range. Is specified for accuracy. Mainstream benchtop multimeters are available with a specific accuracy of better than ±0.01%.
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