JPS63316515A - Proximity sensor - Google Patents

Abstract

PURPOSE:To distinguish and recognize between a magnetic substance and a good conductor by making coincident the resonance frequency of a resonance circuit and the frequency of a resonator, changing the inductance of the detecting coil of the resonance circuit when an object to be is detected close to the detecting coil and generating a phase difference at the voltage of the connecting point of a serial circuit and an oscillator. CONSTITUTION:When the inductance of a detecting coil 1 is L, an initial value when an object to be detected is not close is Lo, the capacity of a capacitor 2 is C, the resistance value of a load resistor 4 is RL and the resistance value in an oscillator 3 is R, an oscillating frequency 50 of the oscillator 3 is made coincident to a resonance frequency 5 of a resonance circuit composed of the detecting coil 1, and the capacitor 2, when the objected to be detected is not closed. A phase comparing circuit 6 outputs a voltage in accordance with the phase difference in the output voltage signal of the oscillator 3 and the double end voltage signal of the load resistor 4. At present, when the double end voltage of the resistor 4 is VL and the output voltage of the oscillator 3 is V0, the V L can be shown by a formula, and a magnetic substance is made close, the L is increased, goes to omega<omega0 and goes to theta>0 and identification can be executed.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a proximity sensor for detecting a highly conductive material such as a magnetic material or metal.

BACKGROUND OF THE INVENTION Conventionally, as shown in FIG. 4, an example of this type of proximity sensor is a resonant circuit consisting of an oscillator 3 having an internal resistance R shown by 5, a detection coil 1 and a capacitor 2 connected to both ends of the oscillator 30. and an output voltage level meter 7 for measuring the voltage across this resonant circuit. By matching the oscillation frequency fo of the oscillator 3 with the center frequency f of the resonant circuit, when the object to be sensed approaches the sensing coil 1, the inductance of the sensing coil 1 changes when the object to be sensed is a conductor. In the case of a magnetic material, the lower value is lower, and in the case of a magnetic material, the lower value is higher, and since the center frequency f of the resonant circuit is shifted, the output voltage level meter 7 indicates a lower value, and the proximity of the object to be detected can be sensed.

Therefore, with this conventional proximity sensor, the output voltage level decreases in the same way whether it is near a magnetic material or a conductive material such as metal, so it had the disadvantage that it was impossible to distinguish between a magnetic material and a metal. .

Problems to be Solved by the Invention The object of the present invention is to provide a proximity sensor that solves the above-mentioned drawback, that is, it is difficult to distinguish whether the detected object is a good conductor such as a metal or a magnetic material. Our goal is to provide the following.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention provides a series connection circuit consisting of an oscillator, a series or parallel resonant circuit of a sensing coil and a capacitor connected to both ends of the oscillator, and a load resistor. , and a phase comparison circuit that receives the voltage at the connection point of the series connection circuit and the voltage of the oscillator and compares the phases of these voltages.

Operation Since the present invention is configured as described above, by making the resonant frequency f of the resonant circuit match the frequency f of the oscillator, when the object to be detected approaches the sensing coil, the sensing coil of the resonant circuit The inductance of the oscillator changes, creating a phase difference between the voltage at the connection point of the series-connected circuit and the voltage of the oscillator, and this is reversed between a magnetic material and a good conductor, so it is difficult to distinguish between them using a phase comparator circuit. can.

Example Next, embodiments of the present invention will be described with reference to the drawings.

Referring to FIG. 1, which shows a circuit diagram of a first embodiment of the present invention, the proximity sensor of the present invention includes an oscillator 3 whose one end is grounded.
, a series resonant circuit consisting of a detection coil 1 and a capacitor 2 connected to the other end of this oscillator 3, a load resistor 4 whose one end is connected to this resonant circuit and whose other end is grounded, and this load resistor 4. It consists of a phase comparator circuit 6 which receives and compares the voltage and the voltage of the oscillator 3.

Next, the operation of this first embodiment will be explained using FIG. 1. First, the inductance of the detection coil 1 is set to the initial value at which the object to be detected is not close, the capacitance of the capacitor 2 is C9, the resistance value of the load resistor 4 is "Le"
Also, the internal resistance value of the oscillator 3 is assumed to be a value. The oscillation frequency fo of the oscillator 3 is made to match one resonance frequency f of a resonance circuit constituted by the detection coil 1 and the capacitor 2 when the object to be detected is not in the vicinity. Further, the phase comparator circuit 6 is connected to the oscillator 3.
A voltage corresponding to the phase difference between the output voltage signal of the load resistor 4 and the voltage signal across the load resistor 4 is outputted.

Next, the voltage vL across the load resistor 4 (RL) is
If the output voltage 'It Vo is ω1------
--, 2°.

It is expressed as c (R-IL). When the sensing object is not close, ω0=ω, and the phase difference is θ−0. When a metal comes close, L decreases, so ω>ω0, and θ×o9. When a magnetic body comes close, L increases, so ω<ω0, and θ>O.

FIG. 2 shows changes in the phase difference θ with respect to changes in the inductance L of the detection coil 1.

However, this is a take calculated assuming ω1=10ω0.

As can be seen from FIG. 2, the phase difference between L and Vo decreases as the inductance increases.

When a metal approaches the detection coil 1, the phase difference increases in the negative direction as the distance to the metal decreases. On the other hand, when the magnetic bodies come close to each other, the inductance L decreases as the distance decreases, and the phase difference increases in the positive direction. Therefore, it can be used as a proximity sensor for both metals and magnetic materials, and it is possible to identify whether a nearby object is metal or magnetic.

Note that the output voltage o of the oscillator 3 cannot be measured directly, but after passing through the internal resistor (R) 5, but if R< RL
It is easy to do so, so it is not a problem.

FIG. 3 shows a second embodiment of the present invention, in which a series resonant circuit consisting of a sensing coil 1 and a capacitor 2 is used in place of the series resonant circuit of the first embodiment. In the case of , the phase of the voltage signal between the terminals of the resonant circuit and the output voltage signal of the oscillator is compared.

Therefore, as in the first embodiment, the phase difference θ between these two signals is reversed between the metal and the magnetic material, and both can be detected.

Furthermore, it is not limited to these first and second embodiments, but if the configuration is such that the phase difference between the voltage signals at two points is appropriately compared by appropriately combining two load resistors, two oscillators, a detection coil, and a capacitor, Any kind of circuit is acceptable.

Effects of the Invention As explained above, according to the present invention, an oscillator, a detection coil, a capacitor forming a resonant circuit with the oscillator,
By having a load resistor and a voltage comparison circuit, it is possible to distinguish and recognize both magnetic materials and good conductive materials such as metals, depending on the positive or negative phase difference between the oscillator voltage and the resonant circuit voltage. effective.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a first embodiment of the present invention, and FIG. 2 is a circuit diagram of a first embodiment of the present invention.
FIG. 3 is a circuit diagram of a second embodiment of the present invention, and FIG. 4 is a circuit diagram of a conventional example. 1...detection coil L, 2...tuning capacitor C13...oscillator, 4...load resistor KL, 5...-oscillator Internal resistance J6・
...Phase comparison circuit. Z7 Ride) Nosa Figure 4

Claims (1)

[Claims] In a proximity sensor having an oscillator, a resonant circuit comprising a detection coil and a capacitor connected to both ends of the oscillator, and an output voltage level meter for measuring the voltage across the resonant circuit, the output voltage level meter is eliminated, and the A load resistor is connected between one end of the resonant circuit and one end of the oscillator, and one terminal receives the voltage at the connection point between the resonant circuit and the load resistor, and the other terminal receives the voltage of the oscillator. A proximity sensor comprising: a phase comparison circuit that receives an output voltage and detects a phase difference therebetween.