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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It can be seen that deflecting torque depends upon eledtrodynamometer multiplication of instantaneous value of current and rate of change of mutual inductance between the fixed and moving coil.

Also it introduces increased frictional losses. It is wound either as self sustaining coil or else on a non-metallic former so as to prevent eddy currents.

Electrodynamometer type Instruments – Construction and Operation

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Advantages of Electrodynamometer Type Wattmeter Following are the advantages of electrodynamometer type wattmeter and they are written as follows: Electrodynamometer type Instruments – Construction and Operation.

As the current through the moving coil shall not exceed tpye, therefore moving coil is shunted by suitable resistance to increase the range of such ammeter.

The controlling torque exerted on the spring is given by.

But the sensitivity of such instrument is low when compared from DC instruments. But moving system, due to inertia cannot follow rapid variations and thus finally meter shows the average torque. At equilibrium the controlling torque and deflecting torques are equal, hence. Since, there is no iron, field strength and hence flux density is proportional to I 1.


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This causes the error in the reading. Instrumfnts is generally wound on a non magnetic metallic former. Fixed coil is provided for the sake of production of magnetic field. It consists of counter weights and pointer.

Electrodynamometer type Instruments – Construction and Operation

We have an idea of the working principle of e lectrodynamometer instrument by taking up a permanent magnet moving coil instrument and considering how it would behave on a. From the principle of conversation of energy. If metal parts would have been used then it would weaken the field of the fixed coil. This is the expression for the instantaneous deflection torque. Therefore it becomes very important to protect the instrument from the effect of external magnetic field.

And the interaction of these two magnetic fields deflects the pointer of the instrument. Errors may be due to pressure coil capacitance. Now we will consider two cases. Change in stored energy. Due to moment of inertia of moving system, the pointer will not follow rapidly changing alternating torque and will fail to show any reading.

Sometimes a suspension may be used, in case a high accuracy is desired. The current cannot be made very high because it may cause excessive heating of springs.


Damping System Air friction damping is used, as eddy current damping will distort the weak operating magnetic field and thus it may leads to error. In electrodynamometer instrumentsthe field can be made of electridynamometer simultaneously with the current in the movable coil if the field fixed coil is connected electrodynamomeyer series with the movable coil.

Thus the instantaneous deflecting torque is given as. Their working depends on the theory that the current carrying conductor placed in a magnetic field experiences a mechanical force.

Stray magnetic field error: Connects Facebook Youtube Videos. Therefore energy input to the instrument.

This site uses Akismet to reduce spam. A suitable shunt is connected to these coils to limit current through them upto desired limit.

electrodynamimeter In this the impedance is equal to its electrical resistance therefore it is purely resistive. This textbook ” Electrical and Electronics Measurements by S. Even earth’s magnetic field considerably affects the reading. If the frequency were very low, the pointer would swing back and forth around the zero points.

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