JPH04415B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application This invention relates to a high-frequency oscillation type proximity switch that uses an oscillation coil of a high-frequency oscillation circuit as a detection coil to detect displacement of an adjacent metal object.

(b) Prior Art If the temperature of the electronic circuit used in the proximity switch is not compensated, the temperature drift of the circuit will directly appear as an error in the detection distance of a metal object. Therefore, the electronic circuit usually includes some kind of temperature compensation means.

For example, FIG. 1 shows a circuit diagram of a conventional high frequency oscillation type proximity switch equipped with temperature compensation means.
In the figure, 10 is an oscillation circuit, 20 is a detection circuit 30 is a comparison circuit, and 40 is an output circuit. D1 and D2 included in the oscillation circuit 10 are oscillation transistors.
This is a diode for temperature compensation of TR1. Also,
The diodes D3 and D4 are provided for temperature compensation of the detection diode D5 and the transistor TR2 of the comparison circuit.

As described above, the conventional high-frequency oscillation type proximity switch requires a relatively large number of components in order to perform temperature compensation, which has disadvantages such as an increase in circuit size and cost.

(c) Purpose The purpose of the present invention is to provide a high frequency oscillation type proximity switch that can perform temperature compensation with a relatively simple configuration.

(D) Configuration The high frequency oscillation type proximity switch of the present invention includes a common base Colpitts oscillation circuit, and an oscillation transistor having a base, an emitter, and a collector constituting the oscillation circuit. an oscillation circuit comprising a second diode connected between the emitter and a resonant circuit connected to the collector and whose oscillation output is fed back to the emitter; and a voltage of the emitter as an output of the oscillation circuit. and an average value circuit that averages this voltage, a comparison circuit that compares the averaged value in the average value circuit with a reference value, and an output circuit that is driven based on the output of the comparison circuit. , a first diode that supplies power to the oscillation circuit and is inserted between the base and emitter of one transistor constituting the comparison circuit via the oscillation circuit and the average value circuit; It is characterized in that the temperature characteristics of the oscillation transistor and the second diode are approximated, and the temperature characteristics of one transistor constituting the comparison circuit and the first diode are approximated.

(e) Embodiment FIG. 2 is a circuit diagram showing the structure of an embodiment of a high frequency oscillation type proximity switch according to the present invention. In this figure, parts equivalent to those in FIG. 1 are indicated by the same reference numerals.

50 is a diode D as the first diode
The oscillator circuit consists of a grounded base Colpitts oscillator circuit powered through 6. The emitter of oscillation transistor TR5 is connected to the cathode of diode D6 via resistor R1. A resonant circuit consisting of coil L1 capacitors C1 and C2 serving as a detection coil is connected to the collector of the oscillation transistor TR5. Further, the emitter is connected to the midpoint of capacitors C1 and C2 via a feedback resistor R2, thereby forming a feedback loop. D7 is a second diode that applies a base bias voltage to the oscillation transistor TR5. The anode of this diode D7 is connected to the cathode of diode D6. The cathode of the diode D7 is connected to the base of the oscillation transistor TR5, and is also grounded via the resistor R3.

Reference numeral 60 denotes an average value circuit comprising a resistor R4 and a capacitor C3, which receives the oscillation output of the oscillation circuit 50 and averages it.

Reference numeral 30 denotes a comparison circuit as means for inputting the oscillation output averaged by the average value circuit 60 and comparing it with a predetermined reference voltage. In this embodiment, a known Schmitt transistor including transistors TR2 and TR3 is used.
Consists of a trigger circuit.

An output circuit 40 is driven based on the output of the comparison circuit 30, and is composed of an output transistor TR4, a protective Zener diode D8, and the like.

Next, the operation of the above embodiment will be explained.

FIG. 3 is an operational waveform diagram of each part of the high frequency oscillation type proximity switch shown in FIG. 2.

Oscillation transistor TR5 in the oscillation circuit 50
The base (point B in the same figure) is the diode D6, D7
Since it is grounded in an alternating current manner, its potential is the potential obtained by subtracting the forward voltages VF ₆ and VF ₇ of diodes D6 and D7 from the power supply V ⁺ , V ⁺ − (VF ₆ +
VF ₇ ) and stable.

On the other hand, capacitors C1 and C2 of the resonant circuit are connected to the emitter of the oscillation transistor TR5 (point C in the figure).
A part of the oscillation output as shown in FIG. 3a is fed back from the connection point (point A in the figure). When this feedback signal is positive, the potential at point C is maintained at a value equal to the potential at point B plus the base-emitter voltage VBE5 of the oscillation transistor TR5. Therefore, the positive part of the feedback signal is clamped at the potential V ⁺ −(VF ₆ +VF ₇ )+VBE5. On the other hand, when the feedback signal is negative, the oscillation transistor TR5 is cut off, so C
A voltage waveform substantially equal to the voltage waveform at point A is obtained at the point. Therefore, the voltage waveform at point C becomes as shown in FIG. 3b.

As a result, the signal at point C is averaged by the average value circuit 60, and as a result, a DC voltage corresponding to the amplitude of the oscillation output appears at point D in the figure. That is, even if the oscillation amplitude changes, since point B is grounded in an AC manner, its potential does not change. The clamp voltage at point C is constant, and only the direction in which the potential decreases changes. Therefore, a change in the oscillation amplitude is obtained as a change in the DC potential at point D.

The signal at point D is given to the comparison circuit 30 and compared with a predetermined reference potential. Thereby, it is detected whether the metal object is located at a predetermined distance from the detection head.

Then, based on the output of the comparison circuit 30, the output circuit 40 is driven.

Next, temperature compensation when the ambient temperature of the circuit increases will be explained.

Due to temperature rise, the forward voltage of diode D6
As a result of VF ₆ decreasing, the voltage supplied to oscillation circuit 50 increases. However, the oscillation transistor TR
Since the base bias voltage of 5 is given by the forward voltage _VF7 of the diode D7, it is not affected by the temperature drift of _VF6 . Here, diode D
If 7 is approximated to the temperature characteristic of the oscillation transistor TR5, the temperature drifts of the two will be canceled out. Therefore, there is no AC temperature drift in this oscillation circuit, and the oscillation amplitude is stable.

Next, DC temperature drift will be explained. The potential at point B becomes V ⁺ − [(VF ₆ −ΔVF ₆ )+(VF ₇ −
ΔVF ₇ )]. The clamp voltage is due to the drift of VBE5 of the oscillation transistor TR5.
The voltage is the potential at point B plus (VBE5 - ΔVBE5). Here, since the temperature characteristics of the diode D7 and the oscillation transistor TR5 are similar, the clamp voltage becomes V ⁺ -(VF ₆ -ΔVF ₆ ). As described above, the oscillation amplitude hardly changes due to temperature rise, so the overall signal level of the oscillation output increases by ΔVF ₆ . Since the temperature drift of the average value circuit 60 can be ignored, the potential at point D increases by ΔVF ₆ after all.

Here, if the temperature characteristics of the transistor TR2 and the diode D6 of the comparator circuit 30 are approximated, the temperature drifts of the two will be canceled out, and the above-mentioned ΔVF ₆
The effect of this does not appear on the output.

Of course, the above temperature compensation is the same even when the ambient temperature drops.

(F) Effects Since the present invention is configured as described above, temperature compensation can be performed with a simpler configuration than the conventional proximity switch.

Therefore, according to the present invention, it is possible to reduce the size and cost of the proximity switch.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a conventional high frequency oscillation type proximity switch equipped with temperature compensation means, FIG. 2 is a circuit diagram showing the configuration of an embodiment of the high frequency oscillation type proximity switch according to the present invention, and FIG. 3 is an operation waveform diagram of each part of the high frequency oscillation type proximity switch shown in FIG. 2. FIG. 10, 50...oscillation circuit, 20...detection circuit,
30... Comparison circuit, 40... Output circuit, 60...
Averaging circuit.

Claims (1)

[Claims] 1. A common-base Colpitts oscillation circuit, and an oscillation transistor having a base, an emitter, and a collector constituting the oscillation circuit, connected between the base and the emitter so as to provide a forward voltage as a base bias voltage. an oscillation circuit comprising a second diode and a resonant circuit in which an oscillation output is fed back to the emitter connected to the collector; and an oscillation circuit that receives the voltage of the emitter as an output of the oscillation circuit and averages this voltage. an average value circuit that converts the average value into a value; a comparison circuit that compares the averaged value in the average value circuit with a reference value; an output circuit that is driven based on the output of the comparison circuit; and a power supply circuit that supplies power to the oscillation circuit. a base of one transistor that supplies and constitutes the comparison circuit;
a first diode inserted between the emitters via the oscillation circuit and the average value circuit, which approximates the temperature characteristics of the oscillation transistor and the second diode; A high frequency oscillation type proximity switch characterized in that the temperature characteristics of the transistor and the first diode are approximated.