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 electrodynamometer for use as a wattmeter is shown in Fig. Wattmeter: Perhaps the most important use of the electrodynamometer is for the wattmeter. electrodynamometer (plural electrodynamometers). An instrument, having a fixed and a moveable coil, that measures the power flowing in an electric circuit;.

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To have reasonable deflecting torque, mmf of the moving coil must be large enough. The current under measurement must not only pass through the movable coil, but also provide the necessary field flux to get a sufficiently strong magnetic field. Thus temperature compensating resistors can be used in the precise instrument to eliminate the temperature errors.

This principle is used in the electrodynamometer type instrument. Hence high mmf is required and the source must have a high current and power.

electrodynamomete Control System Out of two controlling systems i. The changes in the frequency causes to change self inductances of moving coil and fixed coil. Thus the deflection is the function of the mean of the squared current. The scale is thus calibrated electrodynammeter terms of the square root of the average current squared i.

Instead of a permanent magnet, the electrodynamometer type instrument uses the current under measurement to produce the necessary field flux.


The resistor controls the current across the moving coil, and it is connected in series with it. A fixed coil, split into two equal halves provides the magnetic field in which the movable coil rotates, as shown in Fig. The electrodynamometer type instruments are often used in accurate a. Torque to ekectrodynamometer ratio: 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.

The PMMC instrument cannot be sued on a. Views Read Edit View history. The torque acts on the coils becomes. Damping is provided by aluminium air vanes moving in a sector shaped chamber. It is air cored. Electromagnetic wattmeters are used for measurement of utility frequency and audio frequency power; other types are required for radio frequency measurements.

It consists of following parts. Leave a Reply Cancel reply Your email address will not be published.

The electrical inventor and entrepreneur, Werner von Siemensused this principle in his electrodynamometer, first described in Fixed Coil The fixed electrodynnamometer is divided into two equal parts and these are connected in series with the load, therefore the load current will flow through these coils. In other projects Wikimedia Commons. For high-power measurements, a calorimeter directly measures heat produced by RF power. Circuit Globe All about Electrical and Electronics.

The working principle of the Electrodynamometer Wattmeter is very simple and easy. It consists of counter weights and pointer.


This is probably due to the fact that a glass cylinder surrounds the mechanism, and protects it from dirt and mechanical damage. If the pressure coil has range of volts, the half of it can be used so that the range becomes volts. Let us see its operation on a.


At higher frequencies, the inertia of the coil is so great that the pointer does not follow the rapid variations of the driving torque and vibrates around the zero mark. The EDM uses the current electroodynamometer measurement to produce the required field flux.

Electrodynamometter necessary field required for the operation of the instrument is produced by the fixed coils. In metal parts of the instrument the eddy current gets produced. This can cause frictional errors in the reading. The pressure coil can also be tapped to change the meter’s range.

Electrodynamometer Wattmeter

The temperature errors are caused due to the self heating of the coil, which causes change in the resistance of the coil. This is the expression for the instantaneous deflection torque.

Arbitrary waveform generator Digital pattern generator Function generator Signal generator Video-signal generator. Errors caused by vibration of moving system. This page was last edited on 11 Augustat Therefore can must be taken while handling them.