Abstract: A system for measuring the "time of flight" or transfer time of a sound wave in a gas by using the relation between the gas temperature and the velocity of the sound wave in the gas, and calculating therefrom the temperature of the gas. The system comprises an emitter, which generates a sound which is coherent in phase, at one frequency or a group of frequencies; a self-correlating decoder and a receiver, which is associated with the emitter, and which sends the sound to a filter system and to an assembly controlled by a microprocessor, which processes the signal coming out of the filter system in a shape similar to a Hamming wave shape in order to determine the absolute maximum value and therefrom determine the transfer time. With this knowledge, it is easy to relate the transfer time to the distance traveled between the emitter and receiver and the known properties of the gas, in order to arrive at the temperature of the gas through which the sound has been sent.

Abstract: The sensor is constituted by a magnetic core with pole pieces and by an electric coil wound on the body of said core. With said coil there are associated a sinusoidal current generator and impedance measurement means. A processor determines the thickness from the measured value of said impedance.

Abstract: This invention relates to a device which permits to transmit and to receive signals through a telephone line by means of an electromagnetic linking brought about in correspondence with at least one inductive element of a telephone set, without any necessity of interrupting the line which feeds the set concerned.