The electrodynamometer type instrument is a transfer instrument. A transfer instrument is one which is calibrated with a d.c. source and used without any. An electrodynamic type instrument consists of Two Fixed Coil, flux is used in Electrodynamic or Electrodynamometer type instrument. This means that the torque in electrodynamometer instruments must have . Electrodynamometer type voltmeters are the most accurate type of.

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These vanes move in a sector shaped chamber. Indeed, their principal use as ammeters and voltmeters in laboratory and measurement work and as standards for calibration of other instruments as their accuracy is very high.

But this deflecting torque is controlled by the spring. Their working depends on the theory that the current carrying conductor placed in a magnetic field experiences a mechanical electrocynamometer. Earlier these fixed coils are designed to carry the current of about amperes but now the modern wattmeter are designed to carry current of ijstruments 20 amperes in order to save power. To reduce the effect of stray magnetic field, the shields must be used for the instruments.

The electrodynamometer type instrument is a transfer instrument. It can be seen that deflecting torque depends upon the multiplication of instantaneous value of current and rate of change of mutual inductance between the fixed and moving coil.

The scale is thus calibrated in terms of the square root of the average current squared i. The PMMC instrument cannot be sued on a. The eddy current electrrodynamometer with the instrument current, to cause change in the deflecting torque, to cause error. Thus we can write. Errors in the pressure coil inductance.


Where, x is the angle. An electrodynamometer type instrument is a moving coil instrument in which the operating field is produced by another coil which is fixed. Let us assume that the current in fixed coil be I 1 and that in moving coil be I 2 as shown in figure below.

In electrodynamometer type wattmetermoving coil works as pressure coil. The Electrodynamometer Wattmeter has two types of coils; fixed and the moving coil.

The supply voltage applies to the moving coil. Fixed coils are wound with fine wire for using as voltmeter, while for ammeters and wattmeters it is wound with heavy wire. Errors may be due to pressure coil capacitance.

All Categories appendix Basic basics of transmission and distribution Batteries C. This site uses Akismet to reduce spam. This is the expression for the instantaneous deflection torque.

This site uses Akismet to reduce spam. The electrical energy input to the instrument. And the value of current is given by the equation. So the expression for the torque can be written as: These springs act insstruments leads to the moving coil. Thus as it is a transfer instrument, there is direct connection between a.

The field produced by electrodynamimeter instruments is very weak. Therefore can must be taken while handling them.

But moving system, due electrofynamometer inertia cannot follow rapid variations and thus finally meter shows the average torque. To get accurate results, these errors must be minimized. In order that the instrument should be able to read a. Hence the current flows through the pressure coil is considered as the total load current.

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Electrodynamometer Wattmeter

The voltage across the pressure coil of the circuit is given as. Let I 1 and I 2 be the current in fixed and moving coil respectively. Errors may be due to mutual inductance effects. Hence moving coil is connected across the voltage and thus the current flowing through this coil is always proportional to the voltage. Insteuments may be due connections.

Electrodhnamometer is wound either as self sustaining coil or else on a non-metallic former so as to prevent eddy electrodynammometer.

When current passes through the fixed and moving coils, both coils produce the magnetic fields. Therefore an introduction of eddy current damping will distort the main magnetic field and hence will introduce appreciable inaccuracy. Controlling torque is provided by two control springs.

Electrodynamometer Type Wattmeter

Electrodynamometer type instruments are used as a. Errors in Electrodynamometer Type Wattmeter Following are the errors in the electrodynamometer type wattmeters: The changes in the frequency causes to change self inductances of moving coil and fixed coil.

Control System Out of two controlling systems i. As the deflecting torque is produced due to the interaction of these two fields, the deflection is proportional to the power supplied to the load. tpe

We will discuss each of them one by one. This type of instrument is known as Elctrodynamometer type instrument. Subscribe to our mailing list and get interesting stuff and updates to your email inbox.