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 instantaneous torque instruents on the pointer of the wattmeter and is given by the equation. The scale is thus calibrated in terms of the square root of the average current squared i.

From the principle of conversation of energy. The resistor controls the current across the moving coil, and it is connected in series with it. This can cause frictional errors in the reading. In this post we will be discussing the torque equation in such instruments.

Your email address will not be published. Fixed coils are wound with fine wire for use as a voltmeter. A transfer electrodynamo,eter is one which is calibrated with a d.

This type of instrument is known as Elctrodynamometer type 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.


Controlling torque is provided by two control springs. Actually this method of reversing the magnetic flux is used in Electrodynamic or Electrodynamometer type instrument. The moving coil is wound either as a self-sustaining coil or else on a non-metallic former. Elecctrodynamometer frequency error can be reduced by having equal time constants for both fixed and moving coil circuits.


It is done by enclosing in a casing high permeability alloy. Electrodynamometer Instruments are widely used as an ammeter, voltmeter and wattmeter. It can be seen that, the fixed coil and moving coil are connected in series and hence carries the same current. This causes the error in the reading.


Figure below elecfrodynamometer the connection arrangement for electrodynamometer voltmeter. Figure below shows an electrodynamometer ammeter. The current and voltage of the fixed and moving coil generate the two magnetic fields. So the expression for the torque can be written as: Air friction damping is provided by aluminium vanes attached to the spindle at the bottom. The field produced by these instruments is very weak.

Scale There is uniform scale which is used in these types of instrument as moving coil moves linearly over a range of 40 degrees to 50 degrees on either side. To get accurate results, these errors must be minimized. The fixed coil connects in series with the circuit whose power consumption use to be measured. September 7, at 1: If the pressure coil is purely resistive, then their current is in phase with the voltage.

It consists of counter weights and pointer.

Electrodynamometer type Instruments – Construction and Operation

This principle is used in the electrodynamometer type instrument. August 8, at This makes the system heavy reducing torque to weight ratio. The changes in the frequency causes to change self inductances of moving instrhments and fixed coil. Note that a high value of resistance is connected in series with the coils. Therefore, the direction of current in the moving coil is same as that in the fixed coil. This means that the torque in electrodynamometer instruments must have a finite value and electrodynamomeher for AC and DC quantity unlike PMMC instruments.

Errors in Electrodynamometer Type Wattmeter Following are the errors in the electrodynamometer type wattmeters: For using electrodynamometer instrument as a wattmeter to measure the power, the fixed coils acts as a current coil and must be connected in series with the load.


Really very gud looking. Due to moment of inertia of moving system, the pointer will not follow rapidly changing lnstruments torque and will fail to show any reading.

The fixed coil is usually air-cored to avoid hysteresis effects when ytpe on AC circuits.

Notify me when new comments are added. Where, x is the angle. A transfer instrument is one that may be calibrated with a d. 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. Let the currents passing through fixed and moving coils be I 1 and I insttuments respectively. Newer Post Older Post Home. This is great one to see your blog last time I see same design to my friend constraction building in chennai.

Electrodynamometer Wattmeter

There are two types of coils present in the electrodynamometer. The eddy current interacts with the instrument current, typr cause change in the deflecting torque, to cause error.

Hnec metal parts should be kept as minimum as possible. An electrodynamometer type instrument is a moving coil instrument in which the operating field is produced by another coil which is fixed.

Now suppose, if we were able to reverse the direction of magnetic flux each time the direction of AC quantity changes through the moving coil then we can have a unidirectional torque.