Working principle of an electronic voltmeter, Electrical Engineering

Assignment Help:

Q. Explain the working principle of an electronic voltmeter.

Sol. Electronic voltmeter

Basic Voltmeter: The addition of a series resistor, or multiplier, converts the basic D' Arsonval movement into a dc voltmeter, as shown in. the multiplier limits the current through the movements so as not to exceed the value of the full-scale deflection current (Ifsd). A dc voltmeter measures the potential differences between two points in a dc circuit and is therefore connected across a source of emf or a circuit component. The meter terminals are generally marked "Pos" and "Neg" since polarity must be observed.

The multiplier is usually mounted inside the case of the voltmeter for moderate ranges up t 500 V. for higher voltages; the multiplier may be mounted separately outside the case on a pair of binding posts to avoid excessive heating inside the case.

 Ayrton Shunt: The current range of the dc ammeter may be further extended by a number of shunts, selected by a range switch. Such a meter is called a multi-range ammeter. Fig. shows the schematic diagram of a multi-range ammeter.

The circuit has four shunts, Ra' Rb' Rc and   R d' which can be placed in parallel with the movement to give four different current ranges. Switch S is a multi-position make-before-break type switch, so that the movement will not be damaged, unprotected in the circuit, without a shunt as the range is changed.

The universal, or Ayrton, shunt of fig. eliminates the possibility of having the meter in the circuit without a shunt. This advantage is gained at the price of slightly higher overall meter resistance.

The Ayrton, shunt provides an excellent opportunity to apply basic network theory to a practical circuit.

Direct current ammeters are commercially available in a large number of ranges, from 20 µA to 50 A full-scale for a self-contained meter and to 500 A for a meter with external shunt. Laboratory-type precision ammeters are providing with a calibration chart, so that the user may correct his reading for any scale errors.  

Multirange Voltmeter: The addition of a number of multipliers, together with a range switch, provides the instrument with a workable number of voltage ranges. Fig. shows a multi-range voltmeter using a four-position switch and four multipliers Ra' Rb' Rc and R d'  for the voltage ranges V1'  V2'  V3 and V4' respectively.

The values of the multipliers can be calculated using the method shown earlier or alternatively, by the sensitivity method. A variation of the circuit of is as shown.

Where the multipliers are connected in a series string and the range selector switcher the appropriate amount of resistance in series with the movement.

This system has the advantage that all multipliers except the first have standard resistance values and can be obtained commercially in precision tolerances. The low-range multiplier R4 is the only special resistor that must be manufactured to meet the specific circuit requirements.

Electronic voltmeters use amplifiers, rectifiers and other circuits to generate a current proportional to the voltage being measured. The current so produced is measured by a permanent magnet moving coil instrument (PMMC) having taut band suspension instead of pivot and jewel mechanics. This type of voltmeter is called as analog voltmeters.

Related Discussions:- Working principle of an electronic voltmeter

Determine frequencies that is in the spectrum analyze, Two sine waves along...

Two sine waves along with periods of 10 ms and 30 ms are added to generate a single waveform. A spectrum analyzer is utilized to examine the frequency contents of the waveform. Wha

Rectifier, the forward resisitance of a semi conductor diode is 10 ohm, two...

the forward resisitance of a semi conductor diode is 10 ohm, two such diodes used in full wave rectifier subjectto a sinusoidal voltage wave form. given by v(t)=308 , sin(100 pi t)

Torque angle, describe torque angle in ships electrical propulsion system

describe torque angle in ships electrical propulsion system

Calculate the voltage regulation, The per-phase synchronous reactance of a ...

The per-phase synchronous reactance of a three-phase, wye-connected, 2.5-MVA, 6.6-kV, 60-Hz turboalternator is 10. Neglect the armature resistance and saturation. Calculate the vo

What is extended memory system, What is XMS? XMS: The memory system is ...

What is XMS? XMS: The memory system is splits in three major parts as: system area, XMS (extended memory system) and TPA (transient program area). The kind of microprocessor in

Short circuit, what is the time of short circuit ?

what is the time of short circuit ?

Why common collector amplifier is known aa emitter follower, Q. Why a commo...

Q. Why a common collector amplifier is called an emitter follower?         When the input voltage goes through its positive half cycle, the output voltage is also seen to go th

Develop an electric equivalent network, Q. For the mechanical spring-mass-f...

Q. For the mechanical spring-mass-friction system shown in Figure, the differential equation relating the force F(t) and the velocity u(t) is given by  where M is themass,D

What are the basic modes of operation of 8255, What are the basic modes of ...

What are the basic modes of operation of 8255? There are two basic modes of operation of 8255, viz. 1. I/O mode. 3. BSR mode. In I/O mode, the 8255 ports work as progr

Write Your Message!

Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd