Electrodynamometer Wattmeter consists of two coils, pressure coil (PC) and current coil (CC). Pressure coil is connected across the circuit. ELECTRODYNAMOMETER. WATTMETER’S. • These instruments are similar in design and construction to electrodynamometer type ammeters and voltmeters. Before we study the internal construction of electrodynamometer wattmeter, it very essential to know the principle of working of electrodynamometer type.

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It is divided into two halves. Unsourced material may be challenged and removed. When a moving coil that is free to rotate is kept under the influence of a current carrying conductor, then automatically a mechanical force will be applied to the moving coil, and this force will make a little deflection of the moving coil.

There is uniform scale is used in these types of instrument as moving coil moves linearly over a range of 40 degrees elevtrodynamometer 50 degrees on either sides. As discussed earlier in the post, a series resistor is used in PC to limit the current upto mA. Therefore, for higher voltages, PC is designed for V. In order to derive these expressions let us consider the circuit diagram given below: Gravity controlled system cannot be employed because they will appreciable amount of errors.

Let the rms voltage of circuit is V and current flowing is I. Following are the errors in the electrodynamometer type wattmeters: Electrical and electronic measuring equipment. Gravity controlled system cannot be employed because they will appreciable amount of errors.

Connects Facebook Youtube Videos. There are two types of coils present in the electrodynamometer. Let I 1 and I 2 be the instantaneous values of currents in pressure and electric current coils respectively. If a pointer is connected with the moving coil, which will move of a scale, then the deflection can be easily measured by connecting the moving coil with that pointer.

In order to derive these expressions let us consider the circuit diagram given below:.

Therefore in circuit were power is quite high, Current Transformer shall be used for the measurement of power. They can be used for both to measure ac as well dc quantities as scale is calibrated for both. So the expression for the torque can be written as: Thus we see that, angular deflection of electrodynamometer is proportional to the active power being measured. Spring Control is used in such instrument for proving controlling torque.


If there is phase difference between voltage and electric current, then expression for instantaneous electric current through electric current coil can be written as As electrodyynamometer current through the pressure coil in very very small compare to electric current through electric current coil hence electric current through the electric current coil can be considered as equal to total load current.

In case of electrodynamometer wattmeter, i 1 is current through PC and i 2 is current through CC. Scale is uniform upto a certain limit. Gravity controlled system cannot be employed because there e,ectrodynamometer be appreciable amount of errors. The sensor element is maintained at a constant temperature by a small direct current. Where, x is the angle. Dynamometer type wattmeter works on very simple principle and this principle can be stated as “when any electric current carrying conductor is placed inside a magnetic field electrodynamimeter, it experiences a mechanical force and due this mechanical force deflection of conductor takes place”.

The resistor controls the current across the moving coil, and it is connected in series with it.

Errors due to stray magnetic field. The voltage limit of moving coil is limited to about V by the power requirement of voltage circuit since most of the power is dissipated in the series resistor of voltage circuit. Air friction damping is used. Moving Iron instruments Principle and operation. The pressure coil can also be tapped to change the meter’s range.

Therefore, a wattmeter is rated not only in watts, but also in volts and amperes. Scale is uniform up to certain limit b. Moving coil moves the pointer with the help of spring control instrument.

Electrodynamometer Type Wattmeter Construction and Working Principle

This mechanical force deflects the pointer which is mounted on the calibrated scale. Errors in Electrodynamometer Type Wattmeter Following are the errors in the electrodynamometer type wattmeters: Waveforms for switched-mode power supplies as used for much electronic equipment may be very far from sinusoidal, leading to unknown and possibly large errors at any power.


Assuming the electrical resistance of the pressure coil be very high hence we can neglect reactance with respect to its resistance. The reduction in current required to maintain temperature is related to the incident RF power.

Electrodynamometer Wattmeter

Earlier these fixed coils are designed to carry the electric current of about amperes but now the modern wattmeter e,ectrodynamometer designed to carry electric current of about 20 amperes in order to save power. The moving is air cored and is mounted on a pivoted spindle and can moves freely. Following are the advantages of electrodynamometer type wattmeters and they are written as follows: The scale is mirror type and knife edge pointer to eliminate reading error due to parallax.

The average deflection torque is obtained by electrodjnamometer the torque from 0 to T limit. Electrical Instruments and Classification of instruments. As simple as other voltmeter and ammeter connection. Moving coil moves the pointer with the help of spring control instrument. 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. An instrument which measures electrical energy in watt hours electricity meter or energy analyser is essentially a wattmeter which accumulates or averages readings.

Hence the instantaneous value of torque can be written as Average value of deflecting torque can be obtained by integrating the instantaneous torque from limit 0 to T, where T is the time period of the cycle.

And the interaction of these two magnetic fields deflects the pointer of the instrument.