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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eelectrodynamic Your email address will not be published. Related pages Measurement of Three Phase Power. Scale There is uniform scale which is used in these types of instrument as moving coil moves linearly over a range of 40 degrees to 50 degrees on either side. Electromagnetic wattmeters are used for measurement of utility frequency and audio frequency power; other types are required for radio frequency measurements. The meter used for this purpose is called a wattmeter, and electrodyhamic instrument that can be applied as a wattmeter is known as a dynamometer, or sometimes as an electrodynamic instrument.

Advantages of Electrodynamometer Type Wattmeter Following are the advantages of electrodynamometer type wattmeter and they are written as follows: Scale is uniform upto a certain limit. The device consists of a pair of fixed coilsknown as current coilsand a movable coil known as the potential coil.

In this the impedance is equal to its electrical resistance therefore it is purely resistive. The instantaneous torque acts on the pointer of the wattmeter and is given by the equation. Electrdynamic, it is much more convenient to have an instrument that indicates power directly. A typical wattmeter in educational labs has two voltage coils pressure coils and a current coil. The deflection is controlled by the controlling torque produced by the springs. Before we study the internal construction of electrodynamometer wattmeterit very essential to know the principle of working of electrodynamometer type wattmeter.


The controlling torque exerted on the spring is given by. Also, on analog wattmeters, the potential coil carries a needle that moves over a scale to indicate the measurement. This particularly affects low power e. Ahmed Faizan Sheikh, M. Because the meter deflection is proportional to the field coil current and to the moving coil current.

The instruments in which the operating field is produced by the fixed coils are known as electrodynamic or dynamometer type instruments.

In electrodynamometer type wattmetermoving coil works as pressure coil. This article needs additional citations for verification. Circuit Globe All about Electrical and Electronics.

The magnetic field in which the lightweight moving coil is situated is generated by passing current through the fixed field coils.

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Leave this field empty. Errors may be due connections. Instruments of this type are used throughout the RF spectrum and can even measure visible light power. You can find new Free Android Games and apps.

A pointer is attached to the spindle which gives deflection. Dynamometer type wattmeter works on very simple principle and this principle can be stated as when any current carrying conductor is placed inside a magnetic field electrodynamiv, it experiences wattneter mechanical force and due to this mechanical force deflection of conductor takes place.

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 electrodybamic reactance with respect to its resistance. Errors may be due to pressure coil capacitance. The potential coil has, as a general rule, a high-value resistor connected in series with it to reduce the current that flows through it.

The moving coil of the instrument has a series resistor eoectrodynamic is connected in parallel with the load. If the pressure coil is purely resistive, then their current is in phase with the voltage. Retrieved from ” https: The sensor element is maintained at a constant temperature by a small direct current.


The reduction in current required to maintain temperature is related to the incident RF power. Views Read Edit View history. Therefore, a wattmeter is rated not only in watts, but also in volts and amperes. And the value of current is given by the equation. The major difference from the PMMC construction is that the permanent magnet is replaced by two coils, as illustrated in figure 1. The moving is air cored and is mounted on a pivoted spindle and can move freely. Moving coil moves the pointer with the help of spring control instrument.

Electrodynamometer Type Wattmeter

By limiting the current, the moving coil is made of light weight which in turn increases the sensitivity of the instrument. It uses for measuring the power of both the AC and DC circuits. The specification for the meter should specify the reading error for different situations. The average deflection torque watgmeter the coil is given as. Let I 1 and I 2 be the instantaneous values of currents in pressure and current coils respectively.

Electrodynamometer Type Wattmeter | Electrical Study App by SARU TECH

Waveforms for switched-mode tyep supplies as used for much electronic equipment may be very far from sinusoidal, leading to unknown and possibly large errors at any power.

If the pressure coil has range of volts, the half of it can be used so that the range becomes volts. The real power divided by the apparent volt-amperes VA is the power factor.

In these instruments, the operating field is produced by the fixed coil instead of a permanent magnet. Limited of current flows through the moving coil so as to avoid heating. The pressure coil can also be tapped to change the meter’s range.