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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Construction and Working Principle Advantages Errors. Now let the applied value of voltage across the pressure coil be Assuming the electrical resistance of the pressure coil be very high hence we can neglect reactance eectrodynamic respect to its resistance.

Also, on analog wattmeters, the potential coil carries a needle that moves over a scale to indicate the measurement. It consists of following parts There are two types of coils present in the electrodynamometer. Power Measurements in Three Phase Circuits. watgmeter

The current coil is connected wlectrodynamic series with the load, carries the load current and the potential coil, connected in parallel with the load, carries the current proportional to the voltage across the load. And the value of current is given by the equation. Errors in Electrodynamometer Type Wattmeter Following are the errors in the electrodynamometer type wattmeters: In practice accuracy can be improved by connecting a fixed elecgrodynamic such as an incandescent light bulb, adding the device in standby, and using the difference in power consumption.

Air friction damping is used, as eddy current damping will distort the weak operating magnetic field and thus it may leads to error. The Electrodynamometer Wattmeter has two types of coils; fixed and the moving coil. Let I 1 and I 2 be the instantaneous values of currents in pressure and electric current coils respectively. Find Free WordPress Themes and plugins. Dynamometer type wattmeter works on very simple principle and this principle can be stated as “when any electric current carrying conductor is placed wattmeer a magnetic fieldit experiences a mechanical force and due this mechanical force deflection of conductor takes place”.


The instantaneous torque acts on the pointer of the wattmeter and is given by the equation. Because fairly large currents are required to set up the necessary field flux, the dynamometer instrument is not as sensitive as a Eletcrodynamic instrument.

And the interaction of these two magnetic fields deflects tyle pointer of the instrument. The readings may be displayed on the device, retained to provide a log and calculate averages, or transmitted to other equipment for further use.

If there is phase difference between voltage and electric current, then expression for instantaneous current through current coil can be written as As current through the pressure coil is very very small compared to the current through current coil hence current through the current coil can be considered as equal to total load current. Please keep doing this. There are limitations to measuring power with inexpensive wattmeters, or indeed with any meters not designed for low-power measurements.

A modern digital wattmeter electrodynammic the voltage and current thousands of times a second. Errors in tpye pressure coil inductance. Errors may be due connections.


Where, x is the angle. Construction and Working Principle of Electrodynamometer Type Wattmeter Now let us look at constructional details of electrodynamometer. This means, of course, the deflection is also proportional the current through the fixed field coils. In electrodynamometer type wattmetermoving coil works as pressure coil. So the expression for the torque can be written as: So in order to limit the electric current we have connect the high value resistor in series with the moving coil.

Let I 1 and I 2 be the instantaneous values of currents in pressure and current coils respectively. Your email address will not be published. These are basically moving coil instruments. The controlling torque is provided by springs which also serve the additional purpose of leading current into and out of the moving coil.

Dynamometer Type Wattmeter Working

wattmetfr Leave a Reply Cancel reply You must be logged in to post a comment. 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 20 amperes in order to save wattmeteer.

For AC powercurrent and voltage may not be in phase, owing to the delaying effects electrodnamic circuit inductance or capacitance. In other words, when the field 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.


For each sample, the voltage is multiplied by the current at the same instant; the average over at least one cycle is the real power.

Electrodynamometer Type Wattmeter | Electrical Study App by SARU TECH

electodynamic The construction of a dynamometer instrument to some extent resembles the PMMC instrument. The moving coil is pivoted between the two parts of the fixed coil and is mounted on the spindle.

The wattmeter is an instrument for measuring the electric power or the supply rate of electrical energy in watts of any given circuit. These coils are called the current coils of electrodynamometer type wattmeter.

Electrodynamometer Wattmeter

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

It is, therefore, called current coil.

The real power divided by the apparent volt-amperes VA is the power factor. The moving is air cored and is mounted on a pivoted spindle and can moves freely.

Therefore, a wattmeter is rated not only in watts, but also in volts and amperes. The major difference from the PMMC construction is that the permanent magnet is replaced by two coils, as illustrated in figure 1.

Moving Coil Moving coil moves the pointer with the help of spring control instrument. The device consists of a pair of fixed coilsknown as current coilsand a movable coil known as the potential coil.

Electronic wattmeters are used for direct, small power measurements or for power measurements at frequencies beyond the range of electrodynamometer-type instruments. The fixed coil produces a field F m and moving coil produces a field F r.

The two circuits electrodynajic a wattmeter can be damaged by excessive current.