Einrichtung zum elektrischen Messen von Abstandsänderungen

1318907 Electro-physical measurement - dimensions WESTINGHOUSE ELECTRIC CORP 28 Oct 1970 [14 Nov 1969] 51135/70 Heading G1N [Also in Division H3] The distance of a metal object is measured by the voltage across an inductive sensor forming the tank-circuit of a high-gain oscillator with D.C. NEGATIVE FEEDBACK to ensure the oscillated drive amplifier works in its LINEAR region. As shown Fig.4, the inductor 14 is connected a drive amplifier comprising a "source-coupled" pair of F.E.T.'s 30, 32 with peak-clipping diodes 52, 54. The outputs of this amplifier are applied to feedback transistors 58, 62, which are energized through a constant-current transistor 64. Tr 58 supplies substantially D.C. negative feedback on line 22 to F.E.T. 32, (H.F. shunted by capacitor 80) while Tr 62 provides a constant current positive feedback through the inductor 14, (whereby the voltage across the inductor is proportional to the Q Factor). This voltage is also applied to a "source-follower" F.E.T. 82 (energized through a constant current transistor 86); rectified by diode 92, and the resulting D.C. signal passed to output transistor 98. In a more simple arrangement, Fig. 5, the inductance is connected to a common emitter pair 104, 106, and the output of Tr104 is applied to a feedback transistor 116 providing positive feedback on line 20 to the inductor and negative D.C. feedback on the base of Tr 106. The transistor 116 is driven from saturation to cutoff at all time thus providing a constant feedback current.