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 voltage across the pressure coil of the circuit is given as. Thus the torque on the moving coil will not change rather it will be unidirectional.

Electrodynamometer type Instruments – Construction and Operation

Fixed Coil The fixed coil is divided into two equal parts instrumentz these are connected in series with the load, therefore the load current will flow through these coils. With some little modifications, it can be used as a wattmeter for the power measurements.

To have reasonable deflecting torque, mmf of the moving coil must be large enough. It is air cored. These coils are air cored.

Electrodynamometer type voltmeters are the most accurate type of AC voltmeters. Due to moment of inertia of moving system, the pointer will not follow rapidly changing alternating torque and will fail to show any reading.

Now we will consider two cases.


Electrodynamometer type Instruments – Construction and Operation

To get accurate results, these errors must be minimized. Deflecting Torque in Ammeter. The moving coils acts as a voltage coil or pressure oil and must be connected across the supply terminals. The eddy current interacts with the instrument current, to cause change in the deflecting torque, to cause error. The electrical energy input to the instrument. The field produced by fixed coil is proportional to the load current while the field produced by the moving coil is proportional to the voltage.

They are used as watt-meters,varmeters and with some modification as power factor meters and frequency meters. We know that instantaneous torque in electrodynamic type instruments is directly proportional to the product of instantaneous values of currents flowing through both the coils and the rate of change of flux linked with the circuit.

Dynamometer type wattmeter works on very simple principle and tpe principle eoectrodynamometer 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. The electrodynamometer type instrument is a transfer instrument.

The instrument consists of a fixed coil and a moving coil.

Electrodynamometer Type Instruments ~ your electrical home

Now let us derive the expressions for the controlling torque and deflecting torques. This means that as the direction of magnetic field changes, the direction of current in moving coil also changes. So the expression for the torque can be written as: In electrodynamometer instrumentsthe field electrodynamometwr be made of reverse simultaneously with the current in the movable coil if the field fixed coil is connected in series with the movable coil.


Limited of current flows through the moving coil so as to avoid heating. Thus the electtodynamometer is the function of the mean of the squared current.

In order to derive these expressions let us consider the circuit diagram given below: If metal parts would have been used then it would weaken the field of the fixed coil. Newer Post Older Post Electrodynamometter.

Electrodynamometer Wattmeter

Control System Out of two controlling systems i. Instead of a permanent magnet, the electrodynamometer type instrument electrodynamomster the current under measurement to produce the necessary elechrodynamometer flux. To provide magnetic shielding, normally electrodynamic type instrument is enclosed in a high permeability alloy. The frequency error can be reduced by having equal time constants for both fixed and moving coil circuits.

Amarnath Reddy I am a graduate in electrical engineering and blogger by passion. Metallic former shall never be used as it will lead eddy current generation due to changing flux.

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