An electrodynamometer is an instrument used for measuring the electric power. The basic principle was laid out in an paper by Wilhelm Weber. 5 Nov An electrodynamic type instrument consists of Two Fixed Coil, flux is used in Electrodynamic or Electrodynamometer type instrument. 5 Nov This means that the torque in electrodynamometer instruments must have . Electrodynamometer type voltmeters are the most accurate type of.

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Gravity controlled system cannot be employed because there will be appreciable amount of errors. Scale is uniform upto a certain limit.

Torque to weight ratio: Thus the deflection is proportional to the product of the two currents and the rate of change of mutual inductance. It can be dated by noting that istruments sold his business to Morris E. Controlling torque is provided by two control springs. This means that as the direction of magnetic field changes, the direction of current in moving coil also changes. 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.

A good amount of screening of the instruments are required to avoid the effect of stray fields.

Electrodynamometer Type Instruments ~ your electrical home

The field produced by these instruments is very weak. Also it introduces increased frictional losses. The scale is thus calibrated in terms of the square root of the average current squared i. Therefore, Deflecting Torque in Ammeter. Errors due to stray magnetic field.

Due to the inertia of instrument, the needle cannot follow instrumsnts rapid change in direction of torque at power frequency and therefore merely vibrates around zero position.

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But there is something called inertia, you better know. An electrodynamometer is an instrument used for measuring the electric power. This type of instrument can be used either as an ammeter or as a voltmeter, but is generally used as a wattmeter. Torque Equation in Electrodynamometer Instruments.

This type of instrument is known as Elctrodynamometer type instrument. The moving coil is mounted on an aluminium spindle.

Fixed coils are wound with fine wire for use as a voltmeter. The electrpdynamometer type instrument is a transfer instrument. Figure below shows an electrodynamometer ammeter. Figure below shows the connection arrangement for electrodynamometer voltmeter. Hence moving coil is connected across the voltage and thus the current flowing through this coil is always proportional to the voltage.

It would have a torque in electrodynamoketer direction during one half of the cycle and an equal effect in the opposite direction during the other half of the cycle.

Thus we can write. Newer Post Older Post Home.

Electrodynamometer Type Wattmeter

Amarnath Reddy I am a graduate in electrical engineering and blogger by passion. This principle is used in the electrodynamometer type instrument. This makes the construction rigid.

Errors may be due to mutual inductance effects. In the figure above, voltmeter is connected between points A and B to measure the voltage drop across it. This requires the transfer type instrument to have same accuracy for both a. Newer Post Older Post Home.

Electrodynamometer type Instruments – Construction and Operation

Thus ideally the needle of PMMC instrument shall swing back and forth around zero position. There are two types of coils present in the electrodynamometer. Sometimes a suspension may be used, in case a high accuracy is desired. In order to measure the power dissipated in an electrical load, it is necessary to measure the current through the load and the potential drop across it. Thus temperature compensating resistors can be used in the precise instrument to eliminate the temperature errors.


Instead of a permanent magnet, the electrodynamometer type instrument uses the current under measurement to produce the necessary field flux. Also the resistivity of the metal parts used must be high, to reduce the eddy currents. Return to Electrical Measurements Home Page. The controlling torque is provided by two springs which also serve the additional purpose of leading the current into and out of the moving coil.

This means that the torque in electrodynamometer instruments must have a finite value and unidirectional for AC and DC quantity unlike PMMC instruments.

Electrodynamometer type Instruments – Construction and Operation

The moving coil is mounted on an aluminium spindle. Newer Post Older Post Home. This instrument can measure AC as well as DC quantities. They are clamped in place against the coil supports. Hence the instantaneous value of torque can be written as Average value of deflecting torque can be obtained by integrating the instantaneous torque from limit 0 to T, where T is the time period of the cycle. 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.

Electrodynamometer type Instruments – Construction and Operation. Electrodynamometer type instruments are used as a. The frequency error can be reduced by having equal time constants for both fixed and moving coil circuits.

Air friction damping is employed in electrodynamic type instrument. Really very gud looking.