A device or instrument actuated by power from one kind of system and in turn supplies power to another system. A Classic example of a transducer is the telephone receiver which is actuated by electric power and supplies acoustic power to the atmosphere. A form of transducer is an air or hydraulic system that will actuate an electric system by pressure on a contact switch. Another and true form of transducer is the thermocouple (q.v.) wherein heat on two dissimilar pieces of metal will create a small, measure. able electric current.
