The wattmeter is an instrument for measuring the electric power in watts of any given circuit. Electromagnetic wattmeters are used for measurement of utility frequency and audio frequency power; other types are required for radio frequency measurements. Contents. 1 Electrodynamic; 2 Electronic. Dynamometer Type Wattmeter Principle: If two coils are connected such Hence an electrodynamic instrument, when connected as shown in. In electrodynamometer type wattmeter, moving coil works as pressure coil. We know that instantaneous torque in electrodynamic type instruments is directly.

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Leave a Reply Cancel reply You must be logged in to post a comment. The moving coil is pivoted between the two parts of the fixed coil and is mounted on the spindle.

Now let us derive the expressions for the controlling torque and deflecting torques. The pointer is fixed on the moving coil which is placed between the fixed coils. Also, on analog wattmeters, the potential coil carries a needle that moves over a scale to indicate the measurement. Find Free WordPress Themes and plugins.

A limited amount of electric current flows through the moving coil so as to avoid heating. The moving is air cored and is mounted on a pivoted spindle and can move freely. Thus, a circuit with a low power factor will eleectrodynamic a low reading on the wattmeter, even when both of its circuits are loaded to the maximum safety limit.

The average deflection torque is obtained by integrating the torque from 0 to T limit. The wattmeter is an instrument for measuring the electric power or the supply rate of electrical energy in watts of any given circuit. In other projects Wikimedia Commons. 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.

Generally, a high resistance is connected in series with the moving coil to limit the current through it. The current coils are connected in series with the circuit, while the potential coil is connected in parallel. Hence the current flows through the pressure coil is considered as the total load current. 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 electric current through the pressure electrodynakic in very very small compare to electric current through electric electrodynamci coil hence electric current through the electric current coil can be considered as equal to total load current.


The two pressure coils can be connected in series or parallel to change the ranges of the wattmeter.

We know that instantaneous 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.

And the value of current is given by the equation. Earlier these fixed coils are designed to carry the current of about amperes but now the modern wattmeter are designed to carry current of about wattmetet amperes in order to save power. Wattmeters vary considerably in correctly calculating energy consumption, especially when real power is much lower than VA highly reactive loads, tyoe. This is because the position of the pointer depends on the power factorvoltage and current. The content is copyrighted to ElectricalAcademia.

The two circuits of a wattmeter can be damaged by excessive current. Errors caused by vibration of moving system. A wattemter type wattmeter essentially consists of two coils called fixed coil and moving coil. The fixed coil is connected in series with the load and carries the circuit current.

Dynamometer Type Wattmeter Working

The fixed coil is divided into two equal parts and these are connected in series tupe the load, therefore the load current will flow through these coils. The moving coil is connected in parallel with the load and carries the current proportional to the voltage.

Instruments of this type are used throughout the RF spectrum and can even measure visible light power.

The meter used for this purpose is called a wattmeter, and the instrument that can be applied as a wattmeter is known as a dynamometer, or sometimes as an electrodynamic electrofynamic. The two fixed coils are air-cored to avoid hysteresis wattmrter when used on AC. The specification for the meter should specify the reading error for different situations. There are two types of coils present in the electrodynamometer. Then, when a current is passed through the moving coil, the moving coil and the meter pointer are deflected.


Electrodynamometer Type Wattmeter

Errors due to stray magnetic field. Hence the instantaneous value of torque can be written as Average value of deflecting torque can be obtained by ytpe the instantaneous torque from limit 0 to T, where T is the time period of the cycle.

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 fieldit experiences a mechanical force and due this mechanical force deflection of conductor takes place”.

The controlling torque exerted on the spring is given by. In other words, when the wattmetet produced by the current carrying moving coil F r tries to come in line with the field produced by the current carrying fixed coil F ma deflecting torque is exerted on the moving system and deflection takes place as shown in figure b. Errors may be due to mutual inductance effects. The instrument whose working depends on the reaction between the magnetic field of electrodynxmic and fixed coils is known as the Electrodynamo-meter Wattmeter.

In this the impedance is equal to its electrical resistance therefore it is purely resistive. Earlier these fixed coils are designed to carry the electric current of about amperes but now the modern wattmeter are designed to carry electric current of about 20 amperes in order to save power. Simple meters may be calibrated to meet specified accuracy only for sinusoidal waveforms.

By limiting the current, the moving coil is made of light weight which in turn increases the sensitivity of the instrument.