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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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In order to derive these expressions let us consider the circuit diagram given below: Thing is that, the magnetic field produced by the fixed coils are very week because of air cored coil.

Electrodynamometer type Instruments – Construction and Operation. Thus temperature compensating resistors can be used in the precise instrument to eliminate the temperature errors.

Electrodynamometer Wattmeter

The frequency error can be reduced by having equal time constants for both fixed and moving coil circuits. The above equation gives the deflecting torque in electrodynamics or electrodynamometer instruments.

An electrodynamometer type instrument is a moving coil instrument in which the operating field is produced by another coil which is fixed. This is great one to see your blog last time I instrumens same design to my friend constraction building in chennai. But electrodynamo,eter is something called inertia, you better know. Because of this change of magnetic flux, the ijstruments on moving coil will also change in each half cycle of AC quantity to be measured.


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. Learn how your comment data is processed. Due to the inertia of instrument, the needle cannot follow the rapid change in direction of torque at power frequency and therefore merely vibrates around zero position.


The average torque for one time period of the currents are given by. The coils are usually varnished.

Related pages Measurement of Three Phase Power. Hence external magnetic field can interact with the operation field to cause change in the deflection, causing the error.

Construction and Working Principle of Electrodynamometer Type Wattmeter Now let us look at constructional details of electrodynamometer. This instrument can measure AC as well as DC quantities. A spirit level may be provided to ensure proper levelling.

For understanding the electdodynamometer principle, first ask yourself what will happen if we connect a PMMC instrument for the measurement of AC quantity? Instrumentx the sensitivity of such instrument is low when compared from DC instruments. Hence the current flows through the pressure coil is considered as the total load current. In order that the instrument should be able to read a.


A suitable shunt is connected to these coils to limit current through them upto desired limit.

Electrodynamometer type Instruments – Construction and Operation

Your email address will not be published. The changes in the frequency causes to change self inductances of moving coil and fixed coil.

Share to Twitter Share to Facebook. If metallic former is used, then it would induce eddy currents in it. Therefore an introduction electrodynamomefer eddy current damping will distort the main magnetic field and hence will introduce appreciable inaccuracy.

The controlling torque exerted on the spring is given by. Since the direction of current is changing in each half cycle, there will be a corresponding change in the direction of magnetic flux.

Indeed, their principal use as ammeters and voltmeters in laboratory and measurement work and as standards for calibration of other instruments as their accuracy is very high. If an electrodynamometer instrument is tjpe with a d.

Electrodynamometer type Instruments – Construction and Operation

The case is supported by adjustable levelling screws. All Categories appendix Basic basics of transmission and distribution Batteries C. Thus we can write.