1.0 Introduction
A voltmeter is an instrument that measures voltages of either direct or alternating electric current on a scale usually graduated in volts millivolts (0.00V) or kilovolts (1000 volts) the typing commercial or laboratory standard voltmeter in use is likely to employ an electromechanically mechanism in which current flows.
Through turns of wire is translated into a reading of voltage. Other types of voltmeter which use electrostatic forces and these are only voltmeters to measure voltage direct rather than by the effect of current. The potentiometer operates by comparing the voltage to be measured with known voltage. It is used to measure very low voltages the electronic voltmeter which has largely replaced the vacuum – tube voltmeter, uses amplification or reification (or both) to measure either alternating or direct – current voltages the current needed to activate the meter movement is not taken from the circuit being measured, hence this type of instrument does not introduce errors of circuit leading.
However, the growth in technology, it has necessitated the use of computer for controlling the output of the voltmeter. Whereby, the display of the voltage being read is being viewed from the monitor. His kind of display could be either graphical or numerical, but the most popular type is that of numerical display, this is achieved by a series of switching actions of a micro controller, whereby the internal flow at the analog inputs.
Meanwhile, one cannot freely talk about the computer controlled ac voltmeter, without first discussing the Analog is digital (AD) converter which has many degrees of complexity associated with testing an (A/D) converter, one of the simplest tests is to apply a known analog input voltage to the converter and use LEDS to display the resulting digital output code.
Voltmeters
Ac electromechanical meter movement comes in two basic arrangements. Those based on Dc movement designed and those engineered for ac use. Permanent – magnet moving coil (pmmc) meter movement will not work correctly if directly connected to alternating current, because the direction ofneele movement will change with each half cycle of the AC.
i. Passing Ac through D' Arsonval Meter
This causes useless flutter of the needle. In order to use a Dc style, meter such as C' arsenal design the alternating current must be rectified into Dc. This is most easily accomplished through the use of devices called Diodes we will see diodes used in a circuit that demonstrates, the creation of harmonic frequencies from a distorted (or rectified) sine wave. Another strategy for a practical ac meter movement is to redesign the movement without the inherent polarity sensitivity of the Dc types. This means that the use of permanent magnet should be avoided.
ii. Iron Vane Electromechanically Meter Movement
Electrostatic attraction between two metals plates separated by air gap is alternative mechanism for generating a needle –movement force proportional to applied voltage. This works just as well for Ac as it does in dc or probably poorly.
The force involved is small much smaller than the magnetic attraction is small much smaller than the magnetic attraction between an energized coil and iron vane and as such these “electrostatics meter movement tends to be fragile and easily disturbed by physical movement.
The material contains electrical diagrams, circuits, illustrations and more (Very detailed)
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