# ELECTRODYNAMOMETER TYPE INSTRUMENTS PDF

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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As the deflecting torque is produced due to the interaction of these two fields, the deflection is proportional to the power supplied to the load. Hence external magnetic field can interact with the operation field to cause change in the deflection, causing the error. Figure below instruents an electrodynamometer ammeter.

Thus temperature compensating resistors can be used in the precise instrument to eliminate the temperature errors. It shows that the deflecting torque is proportional to the product of currents flowing in the fixed and the moving coil. From equation 12 and 3. The temperature errors are caused due to instrument self heating of the coil, which causes change in the resistance of the coil.

The frequency error can be reduced by having equal time constants for both fixed and moving coil circuits. If an electrodynamometer instrument is calibrated with a d. It is wound either as self sustaining coil or else on a non-metallic former so as to prevent eddy currents.

Controlling torque is provided by two control springs. The above equation gives the deflecting torque in electrodynamics or electrodynamometer instruments.

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For understanding the working principle, first ask yourself what will happen if we connect a PMMC instrument for the measurement of AC quantity? Errors due to stray magnetic field. The moving is air cored and is electrodynamoneter on a pivoted spindle and can move freely. Hence moving coil is connected across the voltage and thus the current flowing through this coil is always proportional to the voltage. The average deflection torque of electrodynamomwter coil is given as.

## Electrodynamometer Wattmeter

The instrument consists of a fixed coil and a moving coil. 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. The value of the current in the pressure coil is very small.

This fixed coil is divided into two sections so that a uniform magnetic field may be achieved at the centre. Besides, their use as an electrodynammeter, voltmeter, and wattmeter; they are also used to transfer calibration of working instruments. Instryments the figure above, voltmeter is connected between points A and B to measure the voltage drop across it.

Scale is uniform upto a certain limit. Let the currents passing through fixed and moving coils be I 1 and I 2 respectively. Stray magnetic field error: Advantages of Electrodynamometer Type Wattmeter Following are the advantages of electrodynamometer type wattmeter and they are written as follows: Your email address will not be published. The moving coil is mounted on an aluminium spindle.

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### Torque Equation in Electrodynamometer Instruments | Electrical Concepts

A uniform field is obtained near the center of coil due to division of coil in two sections. The damping torque is provided by air friction, by a pair of aluminium vanes which are attached to the spindle at the bottom. This site uses Akismet to reduce spam. Errors may be due to mutual inductance instrumwnts. Please keep doing this.

### Electrodynamometer type Instruments – Construction and Operation

Thus to find the mechanical energy, we need to find the change in stored energy in the magnetic field of insstruments coil. The instantaneous torque acts on the pointer of the wattmeter and elecrrodynamometer given by the equation. The field produced by fixed coil is proportional to the load current while the field produced by the moving coil is proportional to the voltage.

The changes in the frequency causes to change self inductances of moving coil and fixed coil. Electrodynamometer type Instruments – Construction and Operation. Newer Post Older Post Home.

Spring provides the controlling torque. Moving Coil Moving coil moves the pointer with the help of spring control instrument. Hnec metal parts should be kept as minimum as possible. Due to moment of inertia of moving system, the pointer will not follow rapidly instrumfnts alternating torque and will fail to show any reading.