ABSTRACT
This chapter introduces the concept of electric power and illustrates the most popular power measurement methods and instruments in dc, ac, and pulse waveform circuits. The instrument most commonly used for power measurement is the dynamometer. It is built by two fixed coils, connected in series and positioned coaxially with space between them, and a moving coil, placed between the fixed coils and equipped with a pointer. The torque produced in the dynamometer is proportional to the product of the current flowing into the fixed coils times that in the moving coil. The working principle of thermal wattmeters is based on a couple of twin thermocouples whose output voltage is proportional to the square of the rms value of the currents flowing into the thermocouple heaters. Wattmeters based on thermal principle allow high accuracy to be achieved in critical cases of highly distorted wide-band spectrum signals.
