High-frequency oscillation type proximity sensor

Abstract

A high-frequency oscillation proximity sensor with an improved detection sensitivity uses, as a detection coil 11, a two-thread coil formed of substantively two coil conductors joined together at their first ends to form a joint connection end and twisted together, one of the two coil conductors being used as a resonance circuit coil L1 and the other as a copper resistance compensation coil L2, and comprises a drive circuit 12 for supplying a drive current to the joint connection end of the two-thread coil to thereby drive the detection coil to oscillate, a buffer 13 for taking out an oscillating output voltage generated at the joint connection end of the two-thread coil, and a phase shift circuit 15 for turning the phase of the oscillating output voltage taken out by the buffer by a predetermined angle and feeding it back to the copper resistance compensation coil to thereby negate the copper resistance of the two-thread coil. The drive circuit comprises a nonlinear amplifier 21 for changing the amplitude of the oscillating voltage generated at the two-thread coil in multiple stages to thereby impart a soft oscillation characteristic to a high-frequency oscillation circuit comprising the nonlinear amplifier and the two-thread coil.

Dependencies are inferred from the claim text.