History[ edit ] On 14 August in Oliver B. Shallenberge patent a watt-hour meter. ChanaRamond L. KraleyEric A. HauptmannBarry and M.

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Circuit Globe Electrical Measurement Electrodynamometer Wattmeter Electrodynamometer Wattmeter Definition: The instrument whose working depends on the reaction between the magnetic field of moving and fixed coils is known as the Electrodynamo-meter Wattmeter. It uses for measuring the power of both the AC and DC circuits. The working principle of the Electrodynamometer Wattmeter is very simple and easy. Their working depends on the theory that the current carrying conductor placed in a magnetic field experiences a mechanical force.

This mechanical force deflects the pointer which is mounted on the calibrated scale. Construction of Electrodynamometer Wattmeter The following are the important parts of the Electrodynamometer Wattmeter. Fixed coil — The fixed coil connects in series with the load. It is considered as a current coil because the load current flows through it. For making the construction easy the fixed coil divide into two parts.

And these two elements are parallel connected to each other. The fixed coil produces the uniform electric field which is essentials for the working of the instruments.

The current coil of the instruments is designed to carry the current of approximately 20 amperes for saving the power. It connects in parallel with the supply voltage.

The current flows through them is directly proportional to the supply voltage. The pointer mounts on the moving coil. The movement of the pointer controls with the help of the spring. The current flows through the coil increases their temperature.

The flows of currents control with the help of resistor which connects in series with the moving coil. Control — The control system provides the controlling torque to the instruments. The gravity control and the spring control are the two types of control system. Out of two, the Electrodynamometer Wattmeter uses spring control system. The spring control system is used for the movement of the pointer. In this Wattmeter the damping torque produces because of the air friction.

The other types of damping are not used in the system because they destroy the useful magnetic flux. Scales and pointers — The instruments use a linear scale because their moving coil moves linearly. The apparatus uses the knife edge pointer for removing the parallax error which causes because of oversights.

Working of Electrodynamometer Wattmeter The Electrodynamometer Wattmeter has two types of coils; fixed and the moving coil. The fixed coil connects in series with the circuit whose power consumption use to be measured. The supply voltage applies to the moving coil. The resistor controls the current across the moving coil, and it is connected in series with it. The pointer is fixed on the moving coil which is placed between the fixed coils.

The current and voltage of the fixed and moving coil generate the two magnetic fields. And the interaction of these two magnetic fields deflects the pointer of the instrument. The deflection of the pointer is directly proportional to the power flows through it. Theory of Electrodynamometer Wattmeter The circuit diagram of the electrodynamometer wattmeter is shown in the figure below.

And the value of current is given by the equation. Hence the current flows through the pressure coil is considered as the total load current. The torque acts on the coils becomes The average deflection torque is obtained by integrating the torque from 0 to T limit. The average deflection torque of the coil is given as The controlling torque exerted on the spring is given by Errors in Electrodynamometer Wattmeter The following are the errors in the Electrodynamometer Wattmeter Pressure Coil Inductance — The pressure coil of the Electrodynamometer has some inductance.

Because of the inductance, the current of the pressure coils lags behind the voltage. Thus, the power factor of the wattmeter becomes lagging, and the meter reads high reading. Pressure Coil Capacitance — The pressure coil has capacitances along with the inductance.

This capacitance increases the power factor of the instrument. Hence causes the error in the reading. Eddy Current Error — The eddy current induces in the coil creates its own magnetic field. This field affects the main current flows through the coil. Thus, the error occurs in the reading. Thus, affect their reading. Temperature Error — The variation in temperature will change the resistance of the pressure coil. The movement of the spring, which provides the controlling torque also affected because of the temperature change.

Thereby, the error occurs in the reading. The calibration of the electrodynamometer wattmeter is same both for the AC and DC measurement. Related terms:.


Electrodynamometer Wattmeter

The electrodynamic wattmeter, shown in figure , uses the reaction between the magnetic fields of two current-carrying coils or sets of coils , one fixed and the other movable. When the current through the fixed-position field winding s is the same as current through the load and the current through the moving coil is proportional to the load voltage, then the instantaneous pointer deflection is proportional to the instantaneous power. Since the moving pointer cannot follow the rapid variations in torque because of its momentum, it assumes a deflection proportional to the average power. The dynamometer-type wattmeter automatically compensates for the power factor error of the circuit under test. It indicates only the instantaneous power resulting from in-phase values of current and voltage. With out-of-phase relationships, a current peak through the moving coil never occurs at the same instant as the voltage peak across the load, resulting in less pointer deflection than when the current and voltage are in phase. The simple meter shown in figure is not compensated.


Electrodynamic or Dynamometer Instruments

Electrodynamic or Dynamometer Instruments In an electrodynamic instrument the operating field is produced by another fixed coil and not by permanent magnet. This instrument can be used as an ammeter or as voltmeter but is generally used as a wattmeter. Refer Fig. Electrodynamic or dynamometer instrument.

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