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 electrodynamometer instrumentsthe field can 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.

Electrodynamometer type Instruments – Construction and Operation

Fixed Coil The fixed coil is divided into two equal parts and these are connected in series with the load, therefore the load current will flow through these coils.

The moving coil is mounted on an aluminium spindle. Errors due to stray magnetic field. They are also used as a transfer electrodynamometter.

Electrodynamometer Type Wattmeter

Hence the current flows through the insturments coil is considered as the total load current. The current cannot be made very high because it may cause excessive heating of springs.

Instrumentss torque insfruments provided by two control springs. Metallic former shall never be used as it will lead eddy current generation due to changing flux. Air friction damping is provided by aluminium vanes attached to the spindle at the bottom. It can be seen that, the fixed coil and moving coil are connected in series and hence carries the same current. Leave a Reply Cancel reply Your email address will not be published.


Electrodynamometer i nstruments are capable of serving as transfer electrovynamometer. Limited of current flows through the moving coil so as to avoid heating. In the figure above, voltmeter is connected between points A and B to measure the voltage drop across it. Your email address will not be published.

Moving coil is serves the purpose of converting the actuating quantity into readable value on the scale.

Let us assume that the current in fixed coil be I 1 and that in moving coil be I 2 as shown in figure below.

Therefore it becomes very important to protect the instrumenhs from the effect of external magnetic field. The moving is air cored and is mounted on a pivoted spindle and can move freely.

Electrodynamometer Wattmeter

This is the expression for the instantaneous deflection torque. They can be used for both to measure ac as well dc quantities as scale is calibrated for both. It is generally wound on a non magnetic metallic former. The electrodynamometer type instruments are often used in accurate a. The eddy current interacts with the instrument current, to cause change in the deflecting torque, to cause error.


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. Pabitha Pabi June 28, at 5: Chand ” is the best in industry.

Electrodynamometer Type Wattmeter

This site uses Akismet to reduce spam. Let us assume an infinitesimally small time dt for the sake of calculation of change in stored energy. Your email address will not be published. It is wound either as self sustaining coil or else on a non-metallic former so as to prevent eddy currents.

Let I 1 and I 2 be the instantaneous values of currents in pressure and current coils respectively. The case is supported by adjustable levelling screws.

Ceramic is usually elecrtodynamometer for mounting supports. Since the direction of current is changing in each half cycle, there will be a corresponding change in the direction of magnetic flux.

The supply voltage applies to the moving coil.