Abstract: A proximity sensor oscillator, having a resonant circuit in which the power loss is inversely related to the distance of a conductive body from a probe containing a part of the resonant circuit, produces an oscillating output signal in the resonant circuit with a peak amplitude that varies with power loss and distance. A power source provides either the current or the voltage component of electrical power at a substantially constant value independent of changes of resonant circuit power loss and is periodically switched to the resonant circuit to provide an average input power thereto. The power loss of the resonant circuit loads the source, and thus the other component of power oscillates within the resonant circuit at a peak amplitude linearly related to the inverse of the power loss.

Abstract: Control of the gate electrode of a magnetic-beam-triode oscillator is effected by a diode connected between the gate and a controllable shunt regulator. The regulator is varied by a voltage derived from a differential amplifier forming part of a closed loop feedback circuit including the oscillator. By introducing an additional differential amplifier, variation of the regulator may also be made to depend on one of several parameters of the oscillator and load circuit, for example on the r.f. tank circuit voltage.

Abstract: A contactless proximity sensor includes an oscillator which generates an output damped by the presence of a metal part whose approach is to be detected. The operating voltage for the oscillator is developed across a capacitor, in parallel with a Zener diode, whose charging circuit includes a high-ohmic resistance connected in series therewith across a supply of pulsating direct current. The flow of charging current into the capacitor is controlled by a thyristor adapted to be fired by means of a trigger transistor upon a critical reduction in the amplitude of the oscillator output. The trigger transistor, upon conducting, lowers the cathode potential of the thyristor whose gate is connected, via a resistor and/or a diode, to the junction of the capacitor with its charging resistance; in one embodiment this gate is driven positive through an inverter upon the conduction of the trigger transistor.