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 damping torque is provided by air friction, by a pair of aluminium vanes which are attached to the spindle at the bottom. From the above two cases, we can have following conclusions: 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. This type of instrument can be used either as an ammeter or as a voltmeter, but is generally used as a wattmeter.

It uses for measuring the power of both the AC and DC circuits.

They can be used for both to measure ac as well dc quantities as scale is calibrated for both. There are two types of coils present in the electrodynamometer. The average deflection torque is obtained by integrating the torque from 0 to T limit. But moving system, due to inertia cannot follow rapid variations and thus finally meter shows the average torque. In order that the instrument should be able to read a. This textbook ” Electrical and Electronics Measurements by S. The controlling torque is provided by springs.

We know that insgruments 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.


Errors in Electrodynamometer Type Wattmeter Following are the errors in the electrodynamometer type wattmeters: They are also used as a transfer instruments. Thus the torque on the moving instruents will not change rather it will be unidirectional.

Electrodynamometer type Instruments – Construction and Operation

Where, x is the angle. Therefore, Deflecting Torque in Ammeter. Electrodynamometer type voltmeters are the most accurate type electrodyanmometer AC voltmeters. Let us see its operation on a. In this post we will be discussing the torque equation in such instruments.

Air friction damping is employed in electrodynamic type instrument. This requires the transfer type instrument to have the same accuracy for both a.

Electrodynamometer Wattmeter

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.

Earlier these typf coils are designed to carry the current of epectrodynamometer amperes but now the modern wattmeter are designed to carry current of about 20 amperes in order to save power.

The field produced by these instruments is very weak. If an electrodynamometer instrument is calibrated with a d. Since, there is no iron, field strength and hence flux density is proportional to I 1.

Torque Equation in Electrodynamometer Instruments | Electrical Concepts

The PMMC instrument cannot be sued on a. This is great one to see your blog last time I instrruments same design to my friend constraction building in chennai.

To provide air friction damping, a pair of aluminium vane is attached to tyep spindle at the bottom. But there is something called inertia, you better know.


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. The moving coil is mounted on an aluminium spindle. Now we will consider two cases. If you carefully observe the figure above, you will notice that Fixed Coil as well as Moving coil is in series.

They are used as watt-meters,varmeters and with some modification as power factor meters and frequency meters. Connects Facebook Youtube Videos.

Your email address will not be published. From equation 12 and 3. The supply voltage applies to the moving coil. The wattmeter indicates the supply power.

Electrodynamometer type Instruments – Construction and Operation

The field produced by fixed coil electrodynamomerer proportional to the load current while the field produced by the moving coil is proportional to the voltage. The pointer is fixed on the moving coil which is placed between the fixed coils. The instrument whose working depends on the reaction between the magnetic field of moving and fixed coils is known as the Electrodynamo-meter Wattmeter.

Leave a Reply Cancel reply Your email address will not be published. To have reasonable deflecting torque, mmf of the moving coil must be large enough. Hence the current flows through the pressure coil is considered as the total load current. However, for an ordinary meter, the inertia is so great that on power frequencies the pointer instrumente not go very far in either direction but merely stays vibrates slightly around zero.