what is wattmeter

A wattmeter is an instrument used to measure the electric active power in watts of any given circuit. It is a device that displays the electrical power of electrically powered devices. A typical wattmeter can measure voltage, current, power, power factor, and energy consumption. The wattmeter reads the average value of the product v(t)i(t) = p(t), where v(t) is the voltage with positive reference polarity at the ± terminal with respect to the other terminal of the potential coil, and i(t) is the current with reference direction flowing into the ± terminal of the current coil. The readings may be displayed on the device, retained to provide a log and calculate averages, or transmitted to other equipment for further use. Wattmeters vary considerably in correctly calculating energy consumption, especially when real power is much lower than VA (highly reactive loads, e.g. electric motors) . Simple meters may be calibrated to meet specified accuracy only for sinusoidal waveforms. There are two types of wattmeters: electromagnetic and electronic. Electromagnetic wattmeters are used for measurement of utility frequency and audio frequency power, while electronic wattmeters are used for direct, small power measurements or for power measurements at frequencies beyond the range of electrodynamometer-type instruments. The traditional analog wattmeter is an electrodynamic instrument, consisting of a pair of fixed coils, known as current coils, and a movable coil known as the potential coil. The digital wattmeter measures the current and voltage on the circuit thousands of times per second and calculates the electrical power by multiplying the current and voltage with the time period. Wattmeters are very sensitive instruments and can be damaged by excessive current, so all wattmeters are rated for a safe maximum current rating.