JPS6313636Y2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a high frequency oscillation type proximity switch.

In general, when this type of proximity switch is made highly sensitive, it becomes more susceptible to the effects of surrounding noise. Noise that enters through the stray capacitance that exists between the detection coil and the surrounding conductor cannot be ignored, which can cause malfunctions, and the influence of stray capacitance changes depending on the grounding condition of the surrounding conductor, causing the detection coil to This can lead to changes in loss and changes in characteristics such as operating distance. In particular, in the case of a type of proximity switch housed in a metal case, the metal case is electrically connected to the surrounding conductor via the mounting member, so stray capacitance is formed between the coil and the metal case. Since the gap therebetween is usually extremely small, the stray capacitance becomes large, and the above-mentioned disadvantages may become noticeable.

The object of this invention is to improve the above-mentioned disadvantages by effectively electrostatically shielding the detection coil, and to provide a proximity switch with increased mechanical strength.

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, a coil bobbin 1 in which a detection coil 11 is formed of insulating synthetic resin, etc.
2, which is housed in a groove of a pot-shaped ferrite core 13 having an E-shaped cross section. The circuit section 21 has a circuit configuration as shown in FIG. 2, and is mounted on a printed circuit board 22. The ferrite core 13, the circuit section 21, etc. are housed in a bottomed cylindrical synthetic resin case 31, and the synthetic resin case 31 is further housed and fixed in a cylindrical metal case 33 with both ends open. In the ferrite core 13, the circuit portion 21 and the like are made of synthetic resin 32.
It is fixed internally by filling it with. Then, the inside of the case 31 is sealed by the rubber packing 34 and the presser plate 35. The cable 23 is sealed inside the case 31 by the rubber packing 34 and the holding plate 35. The cable 23 passes through the rubber packing 34 and the holding plate 35 and is pulled out. A male thread is formed on the outer surface of the metal case 33, so that it can be fixed by attaching a nut or the like to the outer surface.

The circuit section 21 is configured as shown in FIG. 2, and the IC 41 includes an oscillation circuit including a detection coil 11 and a resonant capacitor 42, and a switching circuit that performs switching according to the oscillation state of this oscillation circuit. It's summery. capacitor 43
is for integration, and capacitor 44 is for smoothing. The transistor 46 is for output, and the Zener diode 47 is for surge absorption.

A conductive thin film 25 made of aluminum or the like is deposited on the back surface and outer peripheral side surface of the ferrite core 13, and is connected to the ground of the circuit section 21 via a lead wire 26. If it is difficult to connect the lead wires 26 by ordinary soldering, it may be done by so-called ultrasonic soldering, which is performed while applying ultrasonic vibration and heat, or by using a conductive adhesive.

By grounding the conductive thin film 25 in this way, the conductive thin film 25 itself acts as an electrostatic shield plate for the detection coil 11, and since ferrite has a certain degree of conductivity, the ferrite core 13 also acts as an electrostatic shield plate. It will work.

Then, as shown in FIG. 3, if a portion where the conductive thin film 25 is not formed is provided on the side surface of the outer circumference so that one electrical turn is not formed on the side surface, no eddy current is generated in the conductive thin film, so the oscillation circuit Do not cause a decrease in Q.

In addition, as shown in Fig. 4, ferrite core 1
A groove is provided on the side surface of 3, and the lead wires at both ends of the detection coil are drawn out from this groove, and the conductive thin film 25 is not vaporized in this groove so that one electrical turn is not created. You can also do that.

In any of the above cases, the conductive thin film 25
The lead wire at both ends of the coil 11 is connected to the ground of the circuit section 21 separately from the lead wires at both ends of the coil. It may also be grounded via 26. In this way, the lead wire can be shared, one wire can be omitted, and resistance to electrostatic noise is improved.

According to this invention, a conductive thin film that does not form an electrical turn is provided on the side surface of the ferrite core that is in contact with the inner wall surface of the bottomed case, and this conductive thin film is electrically connected to the ground of the circuit section, so that detection is possible. It is possible to shield noise that enters through the stray capacitance that exists between the coil and the surrounding conductor, and in particular provides excellent electrostatic shielding against noise that enters from the side of the case. In addition, since a conductive thin film is formed on the side surface so as not to form one electrical turn, eddy current does not flow in the conductive thin film and the Q of the oscillation circuit is
Therefore, it is possible to provide a proximity switch with high detection accuracy.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view showing one embodiment of the present invention, FIG. 2 is a circuit diagram thereof, and FIGS. 3 and 4 are perspective views showing the appearance of a ferrite core. DESCRIPTION OF SYMBOLS 11... Detection coil, 13... Ferrite core, 21... Circuit part, 25... Conductive thin film, 33...
...Metal case.

Claims (1)

[Claims for Utility Model Registration] A detection coil that responds to the approach of a detected object, a ferrite core arranged to surround this detection coil, and a ferrite core that forms an oscillation circuit together with the detection coil and responds to the approach of the detected object. A proximity switch having a circuit section that generates a detection output of a detected object based on a change in an oscillation state, and a bottomed case that houses the ferrite core and the circuit section, the proximity switch being in contact with an inner wall surface of the bottomed case. A proximity switch characterized in that a conductive thin film not forming one electrical turn is provided on a side surface of the ferrite core, and the conductive thin film and the ground of the circuit section are electrically connected.