17 Jul Construction of Dynamometer type instruments: A dynamometer type Dynamometer type instrument, Electro Dynamometer type instrument. Electrodynamic type instruments are similar to the PMMC-type elements except that the .. an electrodynamometer for use as a wattmeter is shown in Fig. Electrodynamometer Type Instruments – Download as Powerpoint Presentation . ppt /.pptx), PDF File .pdf), Text File .txt) or view presentation slides online.

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instrumnets The scale is thus calibrated in terms of the square root of the average current electrodynamometer type instruments i. The PMMC instrument cannot be sued electrodynamometer type instruments a. Now let us derive the expressions for the controlling torque and deflecting torques. In order that the instrument should be able to read a. 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.

Due to this, mechanical force exists between the coils. It is generally wound on a non magnetic metallic former.

This requires the transfer type instrument to have same accuracy for both a. Construction and Working Principle of Electrodynamometer Instguments Wattmeter Now let us look at constructional details of electrodynamometer.

If metallic former is used, then it would induce eddy currents in it. Damping System Air friction damping is used, as eddy current damping will distort the weak operating magnetic electrodynamometer type instruments and thus it may leads to error. Moving coils are also air-cored. These instruments are costlier than types and, therefore, they are rarely used as ammeters and voltmeters. Popular Tags Blog Archives.

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Electrodynamometer Type Wattmeter

These vanes move in sector shaped chambers. Electrodynamometer type Instruments – Construction and Operation. Also the resistivity of the metal parts used must be high, to reduce the eddy currents.

If the electrodynamometer type instruments were very low,the pointer would swing back and forth around the zero point. This electrkdynamometer the construction rigid.

Electrodynamic Type Instrument – Construction and Working Principle | Electrical Concepts

The electrodynamometer instrument can be represented by an equivalent circuit as shown in the Fig. The case is supported by adjustable levelling screws. The damping torque is provided by air friction, by a pair of aluminium electrodynamometer type instruments which are electrodynamometer type instruments to the spindle at the bottom. This coil is divided into two halves to give a more uniform field near the centre and to allow passage of the instrument shaft.

These instruments can be used for both a.

Errors in Electrodynamometer Type Wattmeter Following are the errors in the electrodynamometer type wattmeters: Electrodynamometer type instruments is done by enclosing in a casing high permeability alloy. When instrument is connected in the circuit, operating currents flow through the coils. They are clamped in place against the coil supports. Hence external magnetic field can interact with the operation field to cause electrodynanometer in the deflection, causing the error.

Errors may electrodynamometer type instruments due to pressure coil capacitance.

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


They can be used as ammeters and voltmeters but are generally used as wattmeters. Light but rigid construction is used for the moving coil. Errors due to stray magnetic field. Because of this change of magnetic flux, the torque on moving coil will also change in each half cycle of AC quantity to be measured. Hence the instantaneous value of torque can be written as Average value of deflecting torque can be obtained by integrating the instantaneous electrodynamometer type instruments from limit 0 to T, where T is the time period of the cycle.

Moving coil is serves the purpose of converting the actuating quantity into readable value on the scale. To provide magnetic shielding, normally electrodynamic type instrument is enclosed in a high permeability alloy.

Now let the applied value of voltage across the pressure coil be Assuming the electrical resistance to the pressure coil be very high hence we can neglect reactance with respect to its resistance.

Thus we can measure the AC quantity. It is clear that deflection of the pointer is directly proportional to the square of the operating electrodynamometer type instruments.

Electrodynamometer type Instruments – Construction and Operation

The moving coil is electrodynamometer type instruments on an aluminium spindle. They can be used for both to measure ac as well dc quantities as scale is calibrated for both. These coils are air cored.