High frequency oscillation type proimity 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.

Description

technical field [0001] The present invention relates to a method for detecting an approaching object by utilizing a change in the oscillating output voltage (amplitude) of the high-frequency oscillating circuit caused by electromagnetic induction between a detection coil constituting a part of the high-frequency oscillating circuit and an object to be detected. High-frequency oscillation type proximity sensor for the detection object. [0002] Especially the present invention relates to such a kind of high-frequency oscillation type proximity switch, and its described detecting coil is actually made of two twisted coil conductors connected in common at one end, and one of the coils is used as a coil for a resonant circuit, At the same time, the other coil serves as a coil for internal resistance compensation. Using this bifilar coil, the internal resistance component (so-called copper resistance component) thereof is virtually (equivalently) short-circuited to improve detectio...

AI Technical Summary

Problems solved by technology

[0010] However, when constructing a soft oscillation circuit that strives to stabilize the above-mentioned operating characteristics and at the same time meet the requirements of extending the detection distance, for example, the above-mentioned feedback circuit must be used to cancel the dependence of the copper resistance Rcu of the detection coil on temperature. On the one hand, it is necessary to change the oscillation amplitude of the high-frequency oscillation circuit according to the change of the Q value of the detection coil, so that there is a problem that its configuration becomes too large.

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