Abstract: A proximity detection system is disclosed including an oscillator circuit which has an electromagnetic resonator characterized by a hollow metallic chamber, an oscillator having negative resistance characteristics fixed in the chamber, and a source of direct current connected in series with the oscillator and the chamber. A radiating iris opening is provided in the chamber of a size and disposition such that oscillation of said oscillator circuit means is damped except in the proximate presence of an object before the iris. A detector responsive to a characteristic change in output in the oscillator circuit produced by the oscillation thereof such as an operational amplifier or comparator produces an output indicative of the presence of an object.

Abstract: A system for detecting changes in the electrical conductivity or capacitance of a fluid occasioned by the passage of a follower element is disclosed which includes a hollow fluid passage such as a flowmeter through which a fluid is caused to pass and is provided with at least one follower element of similar cross sectional shape to that of the passage and of a size slightly smaller than the passage which is free to move along the passage and has electrical conductance or capacitance properties substantially different from the fluid. At least one electrically-conductive sensor is disposed in the passage in electrical communication with the fluid. A detector circuit is utilized to sense changes in conductance or capacitance through said fluid in accordance with the presence of said follower element in the conductive path.