ELECTRONIC WATTMETER

An electronic wattmeter (transducer) to measure the average power to a load or on an electric power line includes a current transformer, a voltage transformer and a power transformer, the primary coil of each transformer being connected to the power line. The secondary coil of the current transformer is connected to a modulator so that changes in current vary the duty cycle, i.e., zero crossings, of a duty cycle modulator-oscillator. The modulator and the secondary of the voltage transformer are connected to an electronic switch whose switchings are controlled by the zero crossings of the oscllator's pulses whose output is a pulse train in which the pulses vary in width dependent upon current and vary in amplitude dependent upon voltage. The switch is connected to a filter whose output is a d.c. voltage which is proportional to the average electric power on the line.