Displacement sensor

Abstract

A displacement sensor is provided. According to the present invention, a parallel resonant circuit (4) consisting of a coil (6) and condensers (8, 10) is installed in output of an NPN transistor (12),and output of the parallel resonant circuit (4) returns to input of the transistor (12), and a Colpitts oscillator circuit (2) is formed to be continuously oscillated. An output level of the transistor (12) is changed by a change in a position of a measured material toward the coil (6). A constant current source (26) continuously supplies a direct current to the coil (6). An RC low pass filter (30) detects a change in a direct current resistance value of the coil (6) from voltage drop due to a direct current flowing through the coil (6). A microcomputer (38) adjusts an output level of the transistor (12) is adjusted based on an output of the RC low pass filter (30).

Description

[0001] This application is a divisional application of a Chinese invention patent application with an application date of January 21, 2015, an application number of 201510030424.7, and an invention title of "displacement sensor". technical field [0002] The invention relates to a displacement sensor which uses a coil to detect the position change of the object to be measured, in particular to compensating the error caused by the change of the resistance value of the coil with temperature. Background technique [0003] As a displacement sensor using a coil, for example, there is an eddy current type displacement sensor. The eddy current displacement sensor utilizes the following principle: When a conductor as an object to be measured approaches a coil through which an alternating current flows, an eddy current flows through the conductor to generate an alternating magnetic field, thereby changing the impedance of the coil. In this eddy current displacement sensor, the impeda...

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Problems solved by technology

[0005] In the above-mentioned displacement sensor, it is necessary to supply the AC current from the oscillator to the coil, so it is necessary to provide an oscillator in addition to the coil, and the circuit configuration becomes complicated.

Moreover, a switch and a switching control circuit for switching between AC current and DC current are required, and the circuit structure becomes more complicated, so it is not suitable to install the displacement sensor in a place where the installation space is small.

In addition, since temperature compensation is performed by supplying a DC current to the coil every predetermined sampling period, displacement detection cannot be performed during this temperature compensation period.

For example, when detecting the displacement of a valve of an internal combustion engine, it is necessary to continuously detect the displacement, and the displacement sensor of Patent Document 1 cannot be used.

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