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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The eddy current interacts with the instrument current, to cause change in the deflecting torque, to cause error.

Now we will consider two cases. Figure below shows the connection arrangement for electrodynamometer voltmeter. Hnec metal parts should be kept as minimum as possible. Therefore energy input to the instrument.

Electrodynamometer type Instruments – Construction and Operation

Air friction damping is employed in electrodynamic type instrument. Spring provides the controlling torque.

Hence the instantaneous value of torque can be written as Average value of deflecting torque can be obtained by integrating the insttruments torque from limit 0 to T, where T is the time period of the cycle. If the pressure electroydnamometer is purely resistive, then their current instrumenys in phase with the voltage. The current and voltage of the fixed and moving coil generate the two magnetic fields. Dynamometer type wattmeter works on very simple principle and this principle can be stated as when any current carrying conductor is placed inside a magnetic fieldit experiences a mechanical force and due to this mechanical force deflection of conductor takes place.


Metallic former shall never be used as it will lead eddy current generation due to changing flux. Learn how your comment data is processed.

Electrodynamometer type Instruments – Construction and Operation

This type of instrument is known as Elctrodynamometer type instrument. In the figure above, voltmeter is connected between points A and B to measure the voltage drop across it. The Electrodynamometer Insgruments has two types of coils; fixed and the moving coil.

Stray magnetic field error: If, however, we were to reverse the direction of the flux each time the current through the movable coil reverses, a unidirectional torque would be produced for both positive and negative halves of the cycle. If the frequency were very low, the pointer would swing back and forth around the zero points. Fixed coils are wound with fine wire for using as voltmeter, while for ammeters and wattmeters it is wound with heavy wire.

Besides, their use as an ammeter, voltmeter, and wattmeter; they are also used to transfer calibration of working instruments. In this the impedance is equal to its electrical resistance therefore it is purely resistive. For understanding the working principle, first ask yourself what will happen if we connect a PMMC instrument for the measurement of AC quantity?

Such a transfer instrument has same accuracy for a. Circuit Globe Knstruments about Electrical and Electronics. Electrodynamometer i nstruments are capable of serving as transfer instruments.


Electrodynamometer Type Wattmeter

Thus the torque on the moving coil will not change rather it will be unidirectional. To reduce the effect of stray magnetic field, the shields must be used for the instruments. Control System Out of two controlling systems i. The working principle of the Electrodynamometer Wattmeter is very simple and easy.

Electrodynamometer Type Wattmeter

Also the resistivity of the metal parts used must be high, to reduce the eddy currents. September 7, at 1: This means that the torque in electrodynamometer instruments must have a finite value and instrument for AC and DC quantity unlike PMMC instruments.

These springs act as leads to the moving coil. The deflection produced in the instrument is proportional to the product of currents flowing in the fixed and the moving electrkdynamometer. Therefore we can write as. They are used as watt-meters,varmeters and with knstruments modification as power factor meters and frequency meters. It is recommended to read before going to understand the torque equation.

This fixed coil is divided into two sections so that a uniform magnetic field may be achieved at the centre.