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# Instrumentation

## Volt-Ohm-Milliammeter (VOM): Definition, Functions & Types

Definition: A common and simple multimeter used in electronic circuits is the volt-ohm-milliammeter or VOM. A VOM is a voltmeter, ammeter, and ohmmeter, all in one. The VOM has the advantages of being inexpensive and portable. It does, however, usually have a low input resistance (in ohms per volt) on …

## Analog Meter Movement | D’Arsonval & Iron Vane Meter Movement

A common type of meter movement measures current and voltage. It is the D’Arsonval movement, or stationary magnet, moving-coil galvanometer, Figure 1. The movement consists of a permanent-type magnet and a rotating coil in the magnetic field. An indicating needle is attached to the rotating coil, Figure 2. Figure 1. …

## Analog Multimeter Working Principle

An analog multimeter is a meter that can measure two or more electrical properties and display the measured properties along calibrated scales using a pointer. Analog multimeter uses an electromechanical component called a D’Arsonval movement to move the pointer along the scales to display measured values when the test leads …

## Electronic Voltmeter Working and Block Diagram

An analog electronic voltmeter uses an electronic amplifier to improve the performance of an electromechanical voltmeter. For example, an electronic voltmeter has a much higher input resistance than an electromechanical instrument, so voltmeter loading effect is considerably reduced. Also, voltage levels that are normally too small for measuring on an …

## Accuracy and Precision in Measurement | Difference between Accuracy and Precision

Analog Meter Accuracy The accuracy of all deflection instruments is specified by the manufacturer as a percentage of full-scale deflection (FSD). For example, a voltmeter with an FSD of 100 V might have its accuracy stated as ±2%. In this case, the maximum possible error at all points on the …

## Maxwell Inductance Bridge Circuit

For measurement of inductance, the Maxwell Bridge shown in figure 1 can be employed. It is seen that the circuit of the Maxwell Bridge is simply a repeat of the series resistance-capacitance bridge, with the capacitors replaced by the inductors. Fig.1: Maxwell Bridge  A disadvantage of this bridge is that the …

## Series Resistance Capacitance Bridge Circuit

One disadvantage of simple Capacitance Bridge is that perfect balance of the bridge is obtained only when Cs and Cx are both pure capacitances (i.e. they have virtually no resistive components). In general, this occurs only with capacitors that have air or mica dielectrics. Capacitors with other types of dielectric …

## Capacitance Bridge Working Principle

AC bridges are used for measurement of inductances and capacitances. All AC bridge circuits are based on Wheatstone bridge. Figure 1(a) shows the circuit of a simple capacitance bridge. Cs is a precise standard capacitor, Cx is an unknown capacitance, and Q and P are standard resistors, one or both …

## Phase Rotation Meter | Phase Sequence Indicator

A phase rotation meter, as shown in figure 1, is a device used to determine the phase order of a three-phase electrical system. In electrical system that contains three phases, AØ, BØ, and CØ, it is important to know the order before a motor or generator is mechanically connected to …

## Digital Multimeter Working Principle

Fig.1: Digital Multimeter There are two main types of multimeters.  One of the first and oldest multimeters is the analog meter, (Figure 2) and the other, now more widely used meter is the digital multimeter (Figure 1). Fig.2: Analog Multimeter Analog Multimeter Analog meters are a multifunctional multimeter that …

## Dynamometer Type Wattmeter Working Principle | Electrodynamometer

In a dc circuit, the power supplied to a load can be determined by measuring the load voltage and current and multiplying them together: P=EI However, it is much more convenient to have an instrument that indicates power directly. The meter used for this purpose is called a wattmeter, and …

## Megohmmeter Working Principle | Megger Working Principle

A high voltage source is required to pass a measurable current through such resistances. Thus, the megger is essentially an ohmmeter with a sensitive deflection instrument and a high voltage source. As illustrated in figure (1), the voltage is usually produced by a hand-cranked generator. The generated voltage may …

## PMMC Instrument Working Principle | Permanent Magnet Moving Coil Instrument

Figure 1 shows the basic construction of a PMMC instrument. A moving-coil instrument contains principally of a permanent magnet to offer a magnetic field and a small lightweight coil pivoted within the field. A soft iron core is included between the poles of the magnet so that the coil …

The opposition that a circuit offers to the flow of AC is called impedance. By measuring the voltage and current in an AC circuit and utilizing the following equation $Z={}^{V}/{}_{I}$ We can obtain the magnitude of circuit impedance. However, it is often desirable to separate impedance into resistive and reactive …