JPH0456411A - Proximity switch - Google Patents

Abstract

PURPOSE:To realize a proximity switch with a stable characteristic by using sufficient amplification factor for an amplifier circuit to allow its output voltage to be saturated, and feeding back the output of the amplifier circuit to a resonance circuit through a feedback resistor. CONSTITUTION:An amplification factor of an amplifier circuit 2 being the component of an oscillation circuit 3 is selected sufficiently high to saturate the amplitude of to output voltage and the output voltage is used to excite a resonance circuit 1 through a feedback resistor 27. The voltage amplitude of the resonance circuit 1 is the amplitude depending almost only on the impedance of the resonance circuit 1 and the resistance of the feedback resistor 27 and immune to a characteristic of electronic devices and temperature change, so that a stable oscillating voltage is obtained. When an object approaches a detection coil 5, the output at the analog terminal of an output circuit 4 is decreased thereby allowing the detection of the object.

Description

[Detailed description of the invention] [Industrial application field] -ll'9Iue! ktB:I-(tbcW1ml
b61'''ゞ51Relates to a proximity switch that detects towing.

[Conventional technology]

A proximity switch detects the approach of a conductive object such as a metal when it approaches the detection coil of an oscillation circuit by attenuating the oscillation amplitude of the oscillation circuit. The circuit shown in is known. Here, the proximity switch includes a resonant circuit 1, an oscillation circuit 3 including an amplifier circuit 2, and an output circuit 14, and the resonant circuit 1 is constructed by connecting a capacitor 6 in parallel with the detection coil 5.

In the oscillation circuit 3, a current is supplied to the resonance circuit 1 from a constant current circuit 7 via a diode 8, and the connection point between the constant current circuit 7 and the diode 8 is connected to the base of a transistor 9 of the amplifier circuit 2, and the transistor A bias voltage is applied to the circuit 9, and the voltage of the resonance circuit jll is amplified. The emitter of the transistor 9 is connected to the reference potential GND via a resistor 10 and a field effect transistor (hereinafter abbreviated as FET) 11, and the collector is connected to a current mirror circuit 14 consisting of two PNP transistors 12 and 13. The output current of the current mirror circuit 14 is connected to flow into the resonant circuit 1.

In the output circuit 4, a series circuit consisting of the collector-emitter of a transistor 15 and two resistors 16 and 17 is connected between the control power source cc and the reference potential GND, and the resistor 17 is connected to a capacitor 18. A connection point between the constant current circuit 7 and the diode 8 is connected to the base of the transistor l5. In addition, there is a resistor 1 between the control power supply VCC and the reference potential GND.
9 is connected to a series circuit of the collector and emitter of a transistor 20, and a connection point between two resistors 16 and 17 is connected to the base of the transistor 200 via a resistor 21. Furthermore, the collector of the transistor 20 is connected to the base of the FET II, and the transistor 20 and the FET II constitute a current amplification factor adjustment circuit 22. capacitor 1
8 is connected as an analog output to an analog terminal 25 and to one input terminal of a comparator 23. The other input terminal of the comparator 23 is connected so that a voltage obtained by dividing the voltage of the control power supply vcc by a variable resistor 24 is inputted as a reference voltage. The output end of the comparator 23 is connected to an external connection terminal 26.

When the object to be detected is away from the detection coil 5, the impedance of the resonant circuit 1 is high, so the voltage generated across the resonant circuit 10 becomes high, and the voltage amplitude of the emitter current of the transistor 15 becomes large, so the smoothed voltage of the capacitor 18 increases. It also becomes more expensive. When the voltage of the capacitor 18 increases, the collector-emitter current of the transistor 20 increases and the FE
The gate voltage of TII decreases and the impedance between the drain and source of this FET II increases, so the emitter current of transistor 9 decreases, and the excitation current of resonant circuit 1 by current mirror circuit 14 also decreases, resulting in a decrease in oscillation circuit 2.
The amplitude of is suppressed.

When the detected object approaches the detection coil 5, eddy current flows through the detected object and the impedance of the resonant circuit 1 decreases! The voltage amplitude of circuit 1 decreases, and the gate voltage of FET II increases due to the completely opposite effect when the detected object is far away, the impedance between its drain and source decreases, and the collector current of transistor 9 increases. Because of this action, the excitation current of the resonant circuit 1 by the current mirror circuit 14 also increases, and the voltage amplitude of the resonant circuit 1 can take an amplitude corresponding to the distance of the object to be detected without becoming completely zero.

That is, the amplitude of the oscillation circuit 3 is smoothed by the capacitor 18, and the amplitude of the oscillation circuit 3 is smoothed by the capacitor 18, and the amplitude of the oscillation circuit 3 is
By adjusting the current amplification factor of the transistor 9 using ETII in ms, an oscillation amplitude corresponding to the distance of the object to be detected is obtained, and the voltage of the capacitor 18 and the output voltage of the comparator 23 are used as the detection output of this proximity switch.

[Problem to be solved by the invention]

The conventional proximity switch is a FET II current amplification factor adjustment circuit.
The relationship between the distance between the object to be detected and the detection coil and the amplitude obtained by the characteristics of the transistor 20 becomes important. Furthermore, there is a problem in that the above relationship changes greatly due to changes in ambient temperature.

An object of the present invention is to provide a proximity switch that provides a stable relationship between distance and amplitude, that is, output, which is less affected by the characteristics of the oscillation circuit device or the ambient temperature.

[Means to solve the problem]

In order to solve the above problems, the present invention provides an oscillation circuit that includes a resonant circuit having a detection coil, an amplifier circuit that amplifies the oscillating voltage of this resonant circuit and feeds it back to the resonant circuit, and an oscillation amplitude of this oscillation circuit that is externally transmitted. A proximity switch equipped with an output circuit that outputs an output, wherein the amplifier circuit has a sufficient amplification factor to saturate its output voltage, and the output of the amplifier circuit is fed back to the resonant circuit via a feedback resistor. shall be.

(Function) The resonant circuit is saturated by an amplifier circuit with a sufficiently high amplification factor and excited through the feedback resistor with a constant voltage amplitude, so the amplitude of the resonant circuit is determined by the feedback resistor and the impedance of the resonant circuit, and the oscillation A stable distance-to-output relationship can be obtained that is less affected by the characteristics of the circuit devices.

(Embodiment) FIGS. 1 and 2 show embodiments of a proximity switch according to the present invention, and the same parts as in FIG. 3 are given the same reference numerals as in FIG. 3.

In Fig. 1, the proximity switch is equipped with an oscillation circuit 3 and an output circuit 4, which generate a resonant circuit 1 and an amplifier circuit 2, as in the conventional one, but this proximity switch has a current amplification rate using an inverting amplifier circuit and an FET. This differs from the conventional one in that it does not have an adjustment circuit and the amplification transistor and current mirror circuit are replaced with an amplification circuit 2 with a sufficiently high amplification factor.

The resonance circuit 1 is constructed by connecting a capacitor 6 in parallel with a detection coil 5.The oscillation circuit 3 is configured by a constant current circuit 7 that supplies current to the resonance circuit 1 via a diode 8, and this constant current circuit The connection point between the resonant circuit @1 and the diode 8 is connected to the input end of the amplifier circuit 2, and the output end of the amplifier circuit 2 is connected to the connection point between the resonance circuit @1 and the diode 8 via the feedback resistor 27.

As in the conventional output circuit 4, a series circuit consisting of the collector-emitter of a transistor 15 and a resistor 17 is connected between the control power supply VCC and the reference potential GND, and a constant current circuit 7 and a diode 8 are connected to the base of this transistor 150. Connection points are connected. Also, capacitor 1 is connected in parallel with resistor 17.
8 is connected, and the voltage of capacitor 18 is connected to analog terminal 2.
5 and one input terminal of the comparator 23.

The other input terminal of the comparator 23 is connected to a control power supply ■.

The voltage obtained by dividing the voltage by the variable resistor 24 is inputted as a reference voltage.

Amplification mouth! Since I2 has a sufficiently large amplification factor, it amplifies the voltage amplitude of the resonant circuit 1 and outputs a substantially rectangular oscillating voltage determined by the voltage of the control power supply VCC. That is, the control power supply V
Since CC is normally stabilized, the amplifier circuit 2 outputs a constant amplitude, and the resonant circuit 1 is excited by the output of the amplifier circuit 2 via the feedback resistor 27, so this voltage is connected to the feedback resistor 27 and the resonant circuit. It becomes a value divided by the ratio of the impedance of l.

Therefore, when the object to be detected approaches the detection coil 5 and the impedance of the resonant circuit 1 decreases, the voltage across it decreases, the base voltage of the transistor 15 decreases, the emitter current of the transistor 15 decreases, and the capacitor 18 The smoothed voltage also decreases, and the output voltage of the analog terminal 25 also decreases. The output voltage of the external connection terminal 26 connected to the output end of the comparator 23 is output when the detected object approaches a predetermined position, depending on the reference voltage of the other input end.

FIG. 2 shows an example in which the amplifier circuit 2 of the oscillation circuit 3 is composed of two transistors 28, 29 and resistors 30, 31, 32. That is, the resonant circuit 1, the constant current circuit 7, and the diode 8 are the same as those of the conventional ones, but the resistor 30, the collector/emitter of the transistor 28, the series circuit of the resistor 31, the emitter/collector of the PNP transistor 29, and the resistor 32 are connected to each other. A series circuit connects the control power supply VCC and the reference potential GND.
The connection point between the constant current circuit 7 and the diode 8 is connected to the base of the transistor 280. Also, the base of the transistor 290 is connected to the resistor 30 and the transistor 28.
connected to the connection point. Further, the feedback resistor 27 is connected to the connection point between the resonant circuit 1 and the diode 8 and the transistor 29
is connected between the collector of the resistor 32 and the connection point of the resistor 32.

Since the connection of the output circuit 4 is exactly the same as that shown in FIG. 1, the explanation thereof will be omitted.

In this embodiment, a current determined by the voltage of the resonant circuit 1 and the resistor 31 flows through the collector of the transistor 28.

Therefore, when the voltage of the resonant circuit l is high, the collector current of the transistor 28 is large, and this collector current flows to the resistor 30. When the voltage drop exceeds the base voltage V of the transistor 29, the transistor 29 becomes conductive, and its collector current flows through the resistor 30. In other words, the output of the amplifier circuit 2 is approximately equal to the control power supply VC.
The voltage becomes C. Also, if the voltage of the resonant circuit 1 is low, the resistor 3
Since the voltage drop at 0 is low and the voltage applied to the base of transistor 29 is low, transistor 29 is turned off and the collector potential of transistor 29 becomes close to reference potential GND. The voltage of such a resonant circuit 1 is the voltage of the transistor 1
5 to the output circuit 4.

If the value of the resistor 31 is made sufficiently small and the collector current amplification factor of the transistor 28 is increased, the resistor 3° and the transistor 29 may be formed into a current mirror circuit as shown in FIG.

〔Effect of the invention〕

As explained above, according to the present invention, the amplification factor of the amplifier circuit constituting the oscillation circuit is set sufficiently high to saturate the amplitude of the output voltage, and the output voltage causes the resonant circuit to oscillate by 1 m via the feedback resistor. As a result, the voltage amplitude of the resonant circuit becomes a voltage determined only by the impedance of the resonant circuit and the feedback resistance, making it unaffected by the characteristics of the electronic device or temperature changes, resulting in a stable oscillation voltage. This has the effect of allowing the object to be detected to be detected.

[Brief explanation of the drawing]

1 and 2 each show an embodiment of a proximity switch according to the present invention, FIG. 1 is a wiring diagram showing one embodiment, FIG. 2 is a wiring diagram showing an embodiment different from FIG. 1, and FIG. FIG. 3 is a wiring diagram showing an example of a conventional proximity switch. Engineering: Resonant circuit, 2: Amplification circuit, 3: Oscillator circuit, 4: Output circuit, 5: Detection coil, 27: Feedback resistor. 5 detection] 1 le Fig. 2

Claims (1)

[Claims] 1) A proximity switch that includes a resonant circuit having a detection coil, an oscillation circuit that includes an amplifier circuit that amplifies the oscillating voltage of this resonant circuit and feeds it back to the resonant circuit, and an output circuit that outputs the oscillation amplitude of this oscillation circuit to the outside. In, the amplification circuit has a sufficient amplification factor so that its output voltage is saturated,
A proximity switch characterized in that the output of the amplifier circuit is fed back to the resonant circuit via a feedback resistor.