JP3256809B2 - Proximity switch device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a proximity switch device for controlling the opening and closing of a door or the like by detecting the approach or contact of a human or other moving object.

[0002]

2. Description of the Related Art For example, Japanese Patent Application Laid-Open No. 58-16421 discloses a prior art of a proximity switch device which controls opening and closing of a door by detecting approach or contact of a human or other moving object. This prior art is based on the main circuit 1
As shown in the figure, the oscillator 2, a detection capacitor 11 buried close to the door and having a capacitance that changes when a moving object approaches, a oscillating output of the oscillator 2 is applied, and A first resonance circuit 3 having an oscillation frequency as a resonance frequency, and a detection capacitor 11 as a part of a component, an oscillation output of the oscillator 2 is applied, and an oscillation frequency of the oscillator 2 is set to a resonance frequency when a moving object does not approach. The second resonance circuit 6 which shifts to a resonance state by an external signal at the time of detuning
And the respective voltages obtained by adding the respective output voltages of the opposite phases detected from the second resonance circuit 6 to the respective resonance voltages detected from the first resonance circuit 3 and subtracting the subtracted output signal from the second resonance circuit 6 Detection circuit 14 for applying an external signal to
And means for driving the door in the opening direction for a predetermined time triggered by the subtraction output signal.

The first resonance circuit 3 is composed of a first capacitor and a coil, and the second resonance circuit 6 is composed of a second capacitor and a coil, a variable capacitance diode 9 and a coaxial cable.
A resonance output of the first resonance circuit 3 is extracted by the first coil 5, and a resonance output of the second resonance circuit 6 is extracted by the second coil 8.

The second coil 8 has a middle point extending therefrom, and is wound in a direction opposite to the direction in which the coil is wound from the middle point to one end and the direction in which the coil is wound from the middle point to the other end. The middle point is connected to one end of the first coil 5, the outputs of the second resonance circuit 6 are taken out by the second coil 8 with opposite polarities, and the output of the first resonance circuit 3 taken out by the first coil 5. It is configured to add a resonance output.

[0005] One end of the second coil 8 is connected to a first detection circuit 12 comprising a diode, a resistor and a capacitor, and the other end of the second coil 8 is connected to a second detection circuit 13 comprising a diode, a resistor and a capacitor. I have.

The output voltage of the second detection circuit 13 and the output voltage of the first detection circuit 12 are applied to the detection circuit 14 to subtract the output voltage of the first detection circuit 12 from the output voltage of the second detection circuit 13. The output voltage of the detection circuit 14 is applied to the variable capacitance diode 9 of the second resonance circuit 6 via the feedback circuit 15 so that the second resonance circuit 6 returns to the resonance state again.

The output of the detection circuit 14 output via the feedback circuit 15 is applied directly to the differential amplifier 16 through a delay circuit 17 comprising a low-pass filter, and the output of the differential amplifier 16 is supplied to a comparator having hysteresis. The output of the comparator 18 drives the door in the opening direction.

When the detection capacitor 11 is not approached or contacted by a person or other moving object, the capacitance of the detection capacitor 11 does not change, and the second resonance circuit 6 is in a resonance state at the oscillation frequency of the oscillator 2. Therefore, as shown in the upper half of FIG. 5, the voltage OA detected by the first coil 5 at the resonance output of the first resonance circuit 3 and the resonance output of the second resonance circuit 6 are connected to one end of the second coil 8. Voltage B _R detected at one winding of two coils 8
And the sum voltage OAB _R is output.

As shown in the lower half of FIG. 5, the other end of the second coil 8 includes a voltage OA obtained by detecting the resonance output of the first resonance circuit 3 by the first coil 5 and a second resonance circuit 6. other side winding voltage B was detected in the resonant output second coil 8 of _R '(the voltage B _R have opposite phases) _R sum voltage OAB with' it is output. The sum voltage OAB _R is detected by the first detection circuit 12, and the sum voltage OAB ′ _R is detected by the second detection circuit 13.

As apparent from FIG. 5, since the voltage OAB _R is equal to the voltage OAB ′ _R , the output of the detection circuit 14 is zero, the output of the comparator 18 is at a high potential, and the door is closed. The drive is in the closed state.

In this state, when a person or other moving object approaches or comes into contact with the detection capacitor 11 and the capacitance of the detection capacitor 11 increases and changes, the second resonance circuit 6 is detuned, as shown in FIG. A voltage OA obtained by detecting the resonance output of the first resonance circuit 3 by the first coil 5 is provided at one end of the second coil 8.
When the output sum voltage OAB _N between voltage B _N detected by the one winding of the second resonant circuit to output a 6 second coil 8, the other end of the second coil 8, the first resonant circuit 3 the sum of the other voltage detected by the windings B of the output voltage was detected output by the first coil 5 OA and the second resonant circuit 6 the second coil 8 _'N (the voltage B _N have opposite phases) voltage OAB _'N is output. The voltage OAB _N is detected by the first detection circuit 12, and the voltage OAB ' _N
Are detected by the second detection circuit 13.

As apparent from FIG. 6, the voltage OAB _N <
Since voltage OAB _'N, detecting circuit 14 outputs a differential voltage of both voltages, the difference voltage, the second resonant circuit is applied to the variable capacitance diode 9 of the second resonant circuit 6 as an external signal 6 is returned to the resonance state again, and is directly applied to the differential amplifier 16 and delayed through the delay circuit 17,
17, the differential amplifier 16 outputs this difference voltage, and the comparator 18 outputs a low potential output by this output.
Drive the door in the opening direction.

In this prior art, the second resonance circuit 6
Is set by adjusting the second capacitor 7, and the detuning of the second resonance circuit 6 from the resonance state is automatically performed by applying an external signal from the detection circuit 14 to the variable capacitance diode 9. It is to be demodulated.

[0014]

However, in this type of proximity switch device, when the proximity switch device is switched from the non-operation state to the operation state, the proximity switch device is switched from the operation state to the non-operation state. Due to a large change in the surrounding environment conditions of the detection capacitor after switching,
The resonance state of the second resonance circuit must be newly set by adjusting the second capacitor, and this adjustment operation requires a certain level of skill. There is a problem that the resonance state setting operation is troublesome.

The setting of the resonance state of the second resonance circuit by adjusting the second capacitor requires a relatively long time because the operation is troublesome, and the operation of the second resonance circuit can be performed within a given operation time. There is a problem that the resonance state setting cannot always be achieved.

Further, in the above-mentioned prior art, the detuning of the second resonance circuit is automatically corrected to the resonance state by the variable capacitance diode. When a sudden change in the capacitance of the detection capacitor occurs, such as when a portion of the second capacitor is exposed, the variable capacitance diode cannot correct the change in the capacitance and cannot automatically return to the resonance state of the second resonance circuit. was there.

Accordingly, the present invention has been made to solve the above-mentioned problems in the prior art, and is intended to reduce the detuning generated in the second resonance circuit of the main circuit of the proximity switch device by applying a voltage from outside the main circuit. It is an object of the present invention to forcibly and automatically demodulate by a signal, and to stably maintain the second resonance circuit of the proximity switch device in a resonance state at all times.

[0018]

According to the present invention, there is provided an oscillator, a detection capacitor for changing a capacitance by approaching or touching a moving object, and an oscillation output of the oscillator. A first resonance circuit that uses the oscillation frequency of the oscillator as a resonance frequency, and the oscillation output of the oscillator is applied as a part of the detection capacitor as a component, and the oscillation frequency of the oscillator is used as the resonance frequency when the capacitance of the detection capacitor does not change. At the same time, a second resonance circuit which shifts to a resonance state by an external signal at the time of detuning, output voltages of opposite phases detected from the second resonance circuit and resonance output voltages detected from the first resonance circuit separately are added. A detection circuit that subtracts the respective voltages and applies a subtraction output signal to the second resonance circuit as an external signal, and a subtraction output signal from the detection circuit. A main circuit having a means for outputting a detection signal for a predetermined period of time, connected to a second resonance circuit of the main circuit, and changing a capacitance by a control signal to bring the second resonance circuit into a resonance state Another object of the present invention is to have a capacitance adjusting body, and to have a resonance control circuit that inputs a subtraction output signal of the detection circuit of the main circuit and outputs a control signal to the capacitance adjusting body when the second resonance circuit is detuned.

At the time of starting, in order to quickly bring the second resonance circuit of the main circuit into a resonance state, the first resonance circuit and the second resonance circuit are controlled by the subtraction output signal from the detection circuit of the main circuit. A resonance state detection circuit that detects a resonance state and outputs a stop signal, and a control signal, which is an arbitrary voltage signal from a reset state by inputting a start signal, is output to a capacitance adjuster. A voltage generation circuit that holds a voltage when a stop signal is input, a start switch that outputs a start signal when turned on, and a first switch that intermittently controls supply of a stop signal from the resonance state detection circuit to the voltage generation circuit. And the first switch which is activated by input of the start signal to turn on the first switch, and which is stopped by input of the stop signal to turn off the first switch. And a switch driver, is good to consist of.

In order to cope with detuning exceeding the demodulation capability of the variable capacitance diode of the second resonance circuit during operation, the resonance control circuit is controlled by the subtraction output signal from the detection circuit of the main circuit. A resonance state detection circuit that detects that the resonance circuit is in a resonance state and outputs a stop signal, and a control signal that is an arbitrary voltage signal from a reset state by input of a start signal to a capacitance adjuster,
Operates by inputting a stop signal, a voltage generation circuit that holds the voltage at the time of inputting the stop signal, a first switch that intermittently controls the supply of the stop signal from the resonance state detection circuit to the voltage generation circuit, and a start signal input. A first switch driver that turns on the first switch and stops by inputting a stop signal to turn off the first switch, and a first resonance circuit and a second resonance circuit that are set in advance by a subtraction output signal from the detection circuit are set in advance. A resonance detuning detection circuit that detects that detuning has occurred outside the specified range and outputs a start signal, a second switch that intermittently controls supply of a start signal from the resonance detuning detection circuit to the voltage generation circuit, A second switch driver that is activated by inputting a signal to turn on the second switch, and is stopped when input of the start signal is stopped. .

[0021]

Since the capacitance adjuster is connected to the second resonance circuit of the main circuit in such a manner as to change the capacitance of the second resonance circuit, when detuning occurs in the second resonance circuit, the resonance control circuit operates. Then, a control signal is output to the capacitance adjuster, and the capacitance of the capacitance adjuster is forcibly changed to a value at which the second resonance circuit enters a resonance state.

If the second resonance circuit demodulates to a resonance state due to a change in the capacitance of the capacitance adjuster due to the operation of the resonance control circuit, the resonance control circuit detects the demodulation of the second resonance circuit and The operation is stopped in a state where the capacitance value of the capacitance adjuster in which the resonance circuit is in the resonance state is maintained, and thereafter, the fine demodulation operation is performed by the automatic demodulation capability of the main circuit.

In the case where the resonance control circuit is configured to quickly bring the second resonance circuit of the main circuit into a resonance state at the time of starting,
When the start switch, which is the power switch of the entire apparatus, is turned on, the main circuit is activated.At this time, the second resonance circuit in the main circuit causes a large capacitance change in the detection capacitor due to a temporal environmental change. Therefore, it cannot be in a resonance state.

On the other hand, when the start switch is turned on, a start signal is input to the voltage generation circuit of the resonance control circuit, so that the voltage generation circuit outputs a control signal, which is a voltage signal, to the capacitance adjuster. The start signal is also input to the first switch driver, and the first switch driver is operated to turn on the first switch.

Since the control signal output from the voltage generation circuit is a voltage signal whose voltage value increases in proportion to the passage of time, the input of this control signal causes the capacitance of the capacitance adjuster to change to the second resonance circuit. In a direction to bring into a resonance state.

The demodulation state of the second resonance circuit is monitored by a resonance state detection circuit to which a subtraction signal which is an output of the detection circuit of the main circuit is input. That is, when demodulation of the second resonance circuit is achieved, the resonance state detection circuit outputs a stop signal, which is a resonance detection signal, to stop the voltage generation circuit. Due to the stop of the voltage generation circuit, the control signal output from the voltage generation circuit stops changing its voltage value, and is continuously applied to the capacitance adjuster while the voltage value at the time of the stop signal input is kept unchanged. You.

The stop signal of the resonance detection circuit is input to the first switch driver at the same time as being input to the voltage generation circuit, and stops the first switch driver.
The first switch driver turns off the first switch by being stopped by the input of the stop signal, and cuts off the subsequent input of the stop signal to the voltage generation circuit. That is, when the resonance control circuit achieves the tuning of the second resonance circuit at the time of starting, the capacity adjustment operation of the resonance control circuit is stopped, and thereafter, the self-returning force to the resonance state of the main circuit itself, specifically, The tuning of the main circuit is maintained by the change in the capacitance of the variable capacitance diode due to the input of an external signal from the detection circuit via the feedback circuit.

In the case where the resonance control circuit is configured to operate when the capacitance of the detection capacitor is large and abrupt and the degree of detuning exceeds the range of the return capability exhibited by the variable capacitance diode, the main circuit By inputting the subtraction signal from the detection circuit to the resonance detuning detection circuit, the detuning state of the main circuit is constantly monitored, and the degree of detuning is determined in advance based on the demodulation capability range of the variable capacitance diode of the main circuit. When the value falls outside the set range, the resonance detuning detection circuit outputs a start signal.

The start signal from the resonance detuning detection circuit is
First, it is input to the second switch driver to turn on the second switch by operating the second switch driver, and to input a start signal from the resonance detuning detection circuit to the voltage generation circuit via the second switch. Then, the voltage generating circuit is operated after being offset.

The start signal from the resonance detuning detection circuit is
Since it is input to the voltage generation circuit and input to the first switch driver, the first switch driver operates to turn on the first switch, and the stop signal, which is the output signal from the resonance state detection circuit, is output at any time. The state can be input to the voltage generation circuit.

When the degree of detuning of the main circuit falls within the set range due to the operation of the voltage generating circuit, the resonance detuning detecting circuit stops outputting the start signal, so that the second switch driver is deactivated. To return the second switch to the off state.

After the resonance detuning detection circuit stops outputting the start signal, demodulation of the second resonance circuit is achieved by the above-described operations of the voltage generation circuit, the capacitance adjuster, and the resonance state detection circuit. Stop circuit operation.

[0033]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a specific circuit configuration of the main circuit 1 and the capacitance adjuster 19. The configuration of the main circuit 1 is the same as that described in the section of the prior art. Omitted. The capacitance adjuster 19 connected in parallel with the variable capacitance diode 9 is composed of a series circuit of one variable capacitance diode and one capacitor, and the control signal from the resonance control circuit 20 is connected to the ground of the variable capacitance diode. The signal is input to the cathode connected to the capacitor on the opposite side of the connected anode. The variable capacitance diode constituting the capacitance adjuster 19 has a voltage-capacity change ratio characteristic shown by a curve b in FIG. 10, and changes the voltage by approximately 1 V with respect to a capacitance change of 0.5p.

FIG. 2 shows an example of a circuit configuration of a resonance control circuit 20 configured to quickly and forcibly bring the second resonance circuit 6 of the main circuit 1 into a resonance state at the time of starting.
The resonance state detection circuit 21 and the first switch 22 are inserted and connected between the terminal A connected to the output terminal of the feedback circuit 15 from which the subtraction signal is output and the terminal B connected to the capacitance adjuster 19. And a series circuit of a voltage generation circuit 24, a start switch 25 as a power switch connected to the voltage generation circuit 24, and a second switch attached to the first switch 22 and connected to the resonance state detection circuit 21 and the start switch 25. And one switch driver 23.

The resonance state detection circuit 21 is turned on and outputs a stop signal when the voltage value of the input subtraction signal falls within a preset range, and the main circuit 1 shown in FIG.
In this embodiment, a single power supply is used, so the voltage value of the subtraction signal in the resonance state is １ ／ of the single power supply Vcc, that is, １ ／ Vcc (7.5 V), as shown in FIG. The range of 0.5V above and below the resonance point, that is,
A range from V1 = 7V to V2 = 8V is set as a set range, and a stop signal is output when the voltage value of the subtraction signal falls within this range.

The voltage generating circuit 24 outputs a control signal for linearly increasing the voltage value from 0 V to 15 V which is the power supply voltage from the time when the power supply voltage is input as a start signal when the start switch 25 is turned on. As shown in FIG. 9, the output characteristic curve a of the control signal is set so as to reach the same voltage value of 15 V as the power supply voltage in 15 seconds from the point 0 when the start signal is input.

FIG. 3 shows that the resonance state of the operating main circuit 1 is as follows.
If any cause (mainly a sudden change in the capacitance of the detection capacitor 11 due to, for example, a sudden change in the environmental conditions in which the detection capacitor 11 is buried) detunes beyond the self-returning capability range to the resonance state, Circuit configuration example of a resonance control circuit 20 configured to drive the capacitance adjuster 19 to quickly and forcibly demodulate the main circuit 1 when the detuning exceeds the demodulation ability exhibited by the variable capacitance diode 9. In place of the start switch 25 in the embodiment shown in FIG. 2, a resonance detuning detection circuit 26 for inputting a subtraction signal between a terminal A and an input terminal of the voltage generation circuit 24,
A series circuit with the second switch 27 is inserted and connected, and a second switch driver 28 connected to the second switch 27 is connected to the resonance detuning detection circuit 26.

The resonance detuning detection circuit 26 constantly monitors the voltage value of the input subtraction signal, and operates and outputs a start signal when the voltage value of the subtraction signal is out of a preset voltage value range. As shown in FIG. 8, specifically, the lower limit value V2 ′ of the voltage value range is set to 2 corresponding to the power supply voltage of 15V.
V and the upper limit V2 'is set to 12V.

FIG. 4 shows an embodiment in which the embodiment shown in FIG. 2 and the embodiment shown in FIG. 3 are combined so that the main circuit 1 is forcibly brought into a resonance state at the time of starting and generated in the operating main circuit 1. In the case where the detuning exceeds the self-returning ability of the main circuit 1 to the resonance state, the configuration example of the control circuit 20 configured to forcibly demodulate the main circuit 1 is shown. Has a configuration in which a start switch 25 is added to the embodiment shown in FIG.

[0040]

Since the present invention has the above-described structure, the following effects can be obtained. Since demodulation of the second resonance circuit is achieved by adding a new capacitance to the second resonance circuit of the detuned main circuit, demodulation of the second resonance circuit can be reliably and quickly achieved. Therefore, a reliable and stable switch operation can be exhibited.

The value of the newly added capacitance is not limited, and can be freely set to a value that enables demodulation regardless of the degree of detuning of the second resonance circuit. The demodulation ability obtained is extremely large, and therefore, the demodulation of the second resonance circuit can be reliably performed with respect to all environmental changes and situation changes, thereby eliminating the need for manual demodulation adjustment work. Can achieve complete automation.

Since the demodulation operation from the detuning state at the time of starting is automatically achieved by the capacitance adjuster without adjusting the capacitor of the second resonance circuit, there is no troublesome resonance adjusting operation at the time of starting. And the quick operation of the proximity switch device can be obtained.

Since there is no need to adjust and change the capacitance of the capacitor of the second resonance circuit, it is possible to quickly and easily return to the steady state after the occurrence of transient detuning.
Thus, a stable operation can be obtained over a long period of time.

[Brief description of the drawings]

FIG. 1 is an overall circuit configuration diagram showing one embodiment of the present invention.

FIG. 2 is a circuit configuration diagram showing one embodiment of a resonance control circuit shown in FIG. 1;

FIG. 3 is a circuit diagram showing another embodiment of the resonance control circuit shown in FIG. 1;

FIG. 4 is a circuit diagram showing still another embodiment of the resonance control circuit shown in FIG. 1;

FIG. 5 is a characteristic diagram illustrating the operation of the main circuit shown in FIG. 1 in a resonance state.

FIG. 6 is a characteristic diagram illustrating the operation of the main circuit shown in FIG. 1 at the time of detuning.

FIG. 7 is a characteristic diagram illustrating an operation of a resonance state detection circuit included in the resonance control circuit.

FIG. 8 is a characteristic diagram illustrating an operation of a resonance detuning detection circuit included in the resonance control circuit.

FIG. 9 is a characteristic diagram illustrating an operation of a voltage generation circuit included in the resonance control circuit.

FIG. 10 is a characteristic diagram showing a voltage-capacity characteristic of a variable-capacitance diode constituting a capacitance adjuster.

[Explanation of symbols]

1; main circuit 2; oscillator 3; first resonance circuit 4; first capacitor 5; first coil 6; second resonance circuit 7; second capacitor 8; second coil 9; variable capacitance diode 10; coaxial cable 11; First detection circuit 13; Second detection circuit 14; Detection circuit 15; Feedback circuit 16; Differential amplifier 17; Delay circuit 18; Comparator 19; Capacitance adjuster 20; Resonance control circuit 21; Resonance state detection Circuit 22; First switch 23; First switch driver 24; Voltage generation circuit 25; Start switch 26; Resonance detuning detection circuit 27; Second switch 28; Second switch driver

Claims (6)

(57) [Claims] An oscillator (2), a detection capacitor (11) for changing the capacitance by approaching or touching a moving object, an oscillation output of the oscillator (2), and an oscillation frequency of the oscillator (2). A first resonance circuit (3) having a resonance frequency, and the oscillator as a part of the detection capacitor (11) as a component.
The oscillation output of (2) is applied and the detection capacitor (1
When the capacitance of (1) does not change, the oscillation frequency of the oscillator (2) is set to the resonance frequency, and at the time of detuning, a second resonance circuit (6) which shifts to a resonance state by an external signal, and a second resonance circuit (6). )
, And subtracts the respective output voltages obtained by adding the resonance output voltages respectively detected from the first resonance circuit (3) to the second resonance circuit (6). ) Is applied as an external signal to the detection circuit (1
4) and a main circuit (1) comprising means for outputting a detection signal for a predetermined time triggered by the subtraction output signal from the detection circuit (14), and the second resonance circuit (6), A capacitance adjuster (19) that changes the capacitance by a control signal to bring the second resonance circuit (6) into a resonance state, and a subtraction output signal of the detection circuit (14) are input, and the second resonance circuit (6 And a resonance control circuit (20) for outputting a control signal to the capacitance adjuster (19) when detuning is performed. 2. A resonance control circuit (20), wherein a first resonance circuit (3) and a second resonance circuit (6) are brought into a resonance state by a subtraction output signal from a detection circuit (14) of a main circuit (1). A resonance state detection circuit (21) that detects that there is a signal and outputs a stop signal, and a control signal, which is an arbitrary voltage signal from a reset state by inputting a start signal, is output to the capacitance adjuster (19), and a stop signal is output. A voltage generation circuit (24) that holds a voltage at the time of inputting a stop signal, a start switch (25) as a power switch that outputs a start signal when turned on, and a voltage generation circuit from the resonance state detection circuit (21). (24) a first switch (22) for intermittently controlling the supply of a stop signal, and the first switch (22) which is activated by input of a start signal to turn on the first switch (22), and which is stopped by input of a stop signal to First switch dry to turn off switch (22) (23) and the proximity switch device according to claim 1 which is constructed from. 3. A resonance control circuit (20), wherein a first resonance circuit (3) and a second resonance circuit (6) are brought into a resonance state by a subtraction output signal from a detection circuit (14) of a main circuit (1). A resonance state detection circuit (21) that detects that there is a signal and outputs a stop signal, and a control signal, which is an arbitrary voltage signal from a reset state by inputting a start signal, is output to the capacitance adjuster (19), and a stop signal is output. A voltage generation circuit (24) that holds a voltage at the time of inputting a stop signal, and a first switch (22) that intermittently controls supply of a stop signal from the resonance state detection circuit (21) to the voltage generation circuit (24). ), A first switch driver (23) that operates by inputting a start signal to turn on the first switch (22), and stops by inputting a stop signal to turn off the first switch (22); The first resonance circuit (3) and the second resonance circuit are obtained by the subtraction output signal from the circuit (14). (6). However,
A resonance detuning detection circuit (26) that detects that the detuning has occurred outside a preset range and outputs a start signal, and a start signal from the resonance detuning detection circuit (26) to the voltage generation circuit (24). A second switch (27) for intermittently controlling supply, and activated by input of a start signal to turn on the second switch (27),
The proximity switch device according to claim 1, further comprising a second switch driver (28) stopped by the stop of the input of the start signal. 4. The proximity switch device according to claim 3, wherein a start switch (25) as a start signal generation source is connected to the voltage generation circuit (24). 5. The proximity switch device according to claim 1, wherein the capacitance adjuster comprises a variable capacitance diode. 6. A detuning range set in advance in a resonance detuning detection circuit (26) is supplied to a second resonance circuit (6) of the main circuit (1) to automatically return to a resonance state by a feedback voltage. 5. The proximity switch device according to claim 3, wherein the variable capacitance diode (9) is set to a return range limit.