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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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. The fixed coil is divided into two equal parts and these are connected in series with the load, therefore electfodynamic load current will flow through these coils.
Electrodynamometer Type Wattmeter
The current and voltage of the fixed and moving coil generate the two magnetic fields. The controlling torque exerted on the spring is given by. The resistor controls the current across the moving coil, and it is connected in series with it.
These coils are called the current coils of electrodynamometer type wattmeter. So wattmerer expression for the torque can be written as: So the expression for the torque can be written as: However, it is much more convenient to have an instrument that indicates power directly.
Hence moving coil is connected across the wattmetr and thus the electric current flowing through this coil is always proportional to the voltage.
Advantages of Electrodynamometer Type Wattmeter Following are the advantages of electrodynamometer type wattmeter and they are written as follows: Gravity control Spring control, only spring controlled systems are used in these types of wattmeter. So in order to limit the current we have wattmeteer the high value resistor in series with the moving coil.
Therefore, a wattmeter is rated not only in watts, but also in volts and amperes.
Gravity controlled system cannot be employed because they will appreciable amount of errors. The lowest measurable current is given as 0.
The device consists of a pair of fixed coilsknown as current coilsand a movable coil known as the potential coil. It uses for measuring the power of both the AC and DC circuits.
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.
An instrument which measures electrical energy in watt hours electricity meter or energy analyser eledtrodynamic essentially a wattmeter which accumulates or averages readings. Because the meter deflection is proportional to the field coil current and to the moving coil current.
The moving coil is pivoted between the two parts of the fixed coil and is mounted on the spindle.
The pointer is fixed on the moving coil which is placed between the fixed coils. The wattmeter is electrodynmaic instrument for measuring the electric power or the supply rate of electrical energy in watts of any given circuit. Thus, the pointer attached to the spindle of the moving coil deflects.
Now let us derive the expressions for the controlling torque and deflecting torques. The deflection is controlled by the controlling torque produced by eledtrodynamic springs. Air friction damping not shown in fig. Wartmeter the pressure coil is purely resistive, then their current is in phase with the voltage. The supply voltage applies to the moving coil. Consequently, its major application is as a wattmeter. Errors due to stray magnetic field.
There are limitations to measuring power with inexpensive wattmeters, or indeed with any meters not designed for low-power measurements.
The average deflection torque is obtained by integrating the torque from 0 to T limit. The two pressure coils can be connected in series or parallel to change the ranges of the wattmeter. Simple meters may be calibrated to meet specified accuracy only for sinusoidal waveforms.
Electrical and electronic measuring equipment. And the value of current is given by the equation. This mechanical force deflects the pointer which is mounted on the calibrated scale.
We know that instantaneous torque electroeynamic 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.