JPS6046124A - Proximity switch - Google Patents

Abstract

PURPOSE:To make a proximity switch make stable operation with respect to the sensitive distance of the switch, by making the current capacity of two transistors of a current mirror circuit which supplies a feedback current to the resonance circuit of the proximity switch different from each other. CONSTITUTION:A feedback circuit which supplies a feedback current from the oscillating circuit 12 of a proximity switch to a resonance circuit 21 which detects the approach of metals, etc., is constituted with a current mirror circuit composed of transistors (TR) 35 and 36. (n) pieces of TRs 36 are connected in parallel with each other so that the current capacity of the mirroring side TR36 of this circuit can be enlarged to (n) times of the current capacity of the mirrored side TR35. When an AC voltage appearing at the upper end of the resonance circuit 21 is represented as V1C and the value of the operating distance adjusting resistance 22 of the switch is represented as R22, the AC component iC of the collector current of a TR33 becomes iC=V1C/nR22. Therefore, the resistance value for obtaining the feedback current can be reduced to 1/n and approach detection stably operates even when the resistance value fluctuates.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a high frequency oscillation type proximity switch.

Generally, this type of proximity switch is constructed as shown in FIG. In this figure, the proximity switch 10 includes a 10 circuit 1 forming a proximity sensor circuit, and a transistor 16 which is added because the output current capacity is insufficient with only this IO circuit.
It is composed of. This IO circuit has an oscillation circuit 2, a comparator 3, an integration circuit 4% comparator 5,
It has an output circuit 6, a constant voltage circuit 7, and a power supply reset circuit 8, and a detection coil 11. A resonance coil 16, a sensitivity adjustment variable resistor 12, a bypass condenser 14, a power supply reset capacitor 15, and the like are externally attached.

The oscillation circuit 2 includes a detection coil 11 and oscillates. When an object approaches this detection coil 11, the oscillation amplitude is attenuated and the oscillation stops! to And this fM
The change in amplitude is compared with voltage by comparator 3, this detection output is further integrated by integration circuit 4, this integrated output is compared with a level comparison voltage provided in comparator 5, and the output of output circuit 6 is determined by the output of the comparator. Control the state.

The conventional oscillation circuit 2 was constructed as shown in FIG. In this figure, 21 is an LO resonance circuit, 22 is an external variable resistor, 31 is a foot current source, and 32 is a transistor (t, t level shift circuit).

Part 1. The electric FF placed at the top end of the 1-C resonant circuit 21
transistor 33 by kl two-level shift circuit 32
is shifted to the operating point which is the active region of transistor 3.
:H, l: Constructed as an emitter follower circuit using the resistor 22 as an emitter resistor. In addition, when L() is an AC voltage V1c which is applied to the terminal 1 of the 411φ circuit 21, the AC component ic of the collector current of the transistor 33 becomes ic=Vlc/a 22 . . . 1]). This current is fed back to the LOC resonance circuit 21 by a current mirror circuit made up of transistors 34 and 35 to cause oscillation. Needless to say, the proximity switch detects when the object to be detected approaches the coil of the LC resonance circuit 21, the oscillation amplitude becomes smaller due to increased coil loss, or the oscillation stops. switching operation. Moreover, the function of the proximity switch is that it is necessary to turn on and off the switch when the detected object approaches the coil V (lined up at a certain distance). However, the coils used in the T and C resonance circuits Since the variation is large, a method of adjusting the gain on the circuit side is generally used to adjust the operating distance.

For this reason, the resistor R22 is not provided in l1l (of To) and is an external component, and after connecting the LOC resonant circuit ■c, the resistor is connected to the object to be detected at a predetermined distance to operate the switch. R22 is trimmed.After that, it is filled with filler for assembly, but since the high frequency voltage generated by the LOC resonant circuit is applied to both ends of the resistor 1't22, The impedance due to stray capacitance due to charging or charging is the resistance R22.
This is not negligible compared to the above, and there is a drawback that the operating distance of the switch deviates from a predetermined distance. Furthermore, this stray capacitance does not vary predictably depending on the botting or filling material and method, and the behavior of the capacitance of the resonant capacitor due to temperature is also unstable1, making the operation of the proximity switch unstable. Ta.

The present invention aims to eliminate such conventional drawbacks, and one practical example of the present invention will be described below with reference to the drawings.

-J" 3 Figure 3 shows a group of 5 transistors in which n diode-connected transistors 36 are connected in parallel compared to the transistor 35 among the transistors 35 and 36 constituting the current mirror, or an area 11 that is 0 times larger than the transistor 35; The other structure, IJv, is the same as that shown in FIG. 2, so a description thereof will be omitted.

Therefore, the feedback current ir in FIG. 3 is 1r=-Vl
c/n 1 (22-121 and k, 11) In order to obtain the same feedback current as in equation 11, that is, to obtain the same gain, R22 = R22/n, and therefore the external resistor 11.22 The value of can be small.

Figure 4 shows that the current amplification factor β of the transistor (P N l)) is (1t:I/C), so the effect of the change in β due to temperature is large.
Attachment 1117 is a circuit that employs a Wilson type current mirror.As mentioned above, this invention compares the amount of current of the mirrored transistor of the current mirror circuit to the current capacity of the mirrored transistor. Since the value of the sensitivity adjustment resistor R22 is set to a large value, the impedance of the stray capacitance attached to both ends of the resistor R22 is reduced. 5 effects can be made relatively small, so even if potting and filling are performed after adjusting the switch sensitive distance, the sensitive distance does not change, and the influence of floating volume changes due to temperature changes is greatly reduced. It has the advantage of stable switching operation over temperature.

[Brief Description of the Drawings] Fig. 1 is a block circuit diagram of a general proximity switch, Fig. 2 is a circuit diagram of a conventional oscillation circuit, Fig. 3 is a circuit diagram of an oscillation circuit of a proximity switch according to the present invention, and Fig. 4 is a circuit diagram of a conventional oscillation circuit. The figure is a circuit diagram showing another embodiment of the invention. 2...Oscillation circuit, 21...LOC resonance circuit 22...
- Sensitivity adjustment resistor, 31.33.34.35...transistor. Patent applicant Yamatake Honeywell Co., Ltd. “0 (■

Claims (1)

[Claims] In an oscillation circuit including a resonant circuit of an oscillation coil and a resonant capacitor, and a change in the oscillation amplitude of this oscillation circuit is guided to an output circuit via an integrating circuit, a feedback circuit that supplies a feedback current to the resonant circuit is used. 1. A proximity switch comprising a current mirror circuit and having a current capacity of a mirrored transistor of the current mirror circuit larger than that of a mirrored transistor.