JPS593284A - Antitheft sensor - Google Patents

Abstract

PURPOSE:To obtain a sensor most suitable in antitheft effect, by a method wherein a predetermined frequency zone is limited and the resonant phenomenon of a sensing coil and a condenser is coincided with the high frequency characteristics of ferrite to make it possible to detect only ferrite. CONSTITUTION:A high frequency current with frequency fr is supplied to a primary coil CL1 from an oscillator 1 having a range of 200kHz-2MHz. A sensing coil CL2 is provided so as to be electromagnetically connected to said coil CL1 and a resonant circuit is constituted from said coil CL2 and the condenser C1. In this constitution, when a ferrite material approaching CL2 is spaced apart therefrom, frequency is shifted to fo. In addition, when a magnetic metal or a non-ferrous metal is brought close thereto, because of attenuation caused by frequency changed corresponding to permeability or counteraction due to an eddy current flowing through a metal, the frequency thereof is changed to f1. As the result, detecting output voltage close to a peak value is obtained to be sent out after multiplication by an amplifier 2.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a complete sheet or card made of ferrite, and the movement of the sheet or card, i.e.
The present invention relates to a sensor that prevents theft of articles by detecting the taking out of articles at all predetermined positions.

As a measure to prevent product theft in supermarkets, etc., magnetic cards containing metal sheets or ferrite are attached to products.2 For example, magnetic sensors are placed at store entrances and exits to detect products being taken out without passing through the cash register. A method is proposed. However, since magnetic sensors detect metals other than the object, their performance is poor and unstable, and the reality is that they are far from practical use. ! A magnetized metal sheet or ferrite sheet is attached to the product, and this is used as a high-sensitivity magnetometer, i.e., a frequency-doubling system that detects twice the frequency. Detection methods are being considered, such as a magnetometer that detects a meter, a quadruple frequency, and a sixfold frequency. However, even with this method, all metal objects other than the target object may be detected, making the method of use complicated and unstable.

The present invention is an attempt to solve the above-mentioned problems and to realize a highly reliable anti-theft system by providing a high-precision anti-theft sensor that does not cause false detection.

The present invention is characterized in that a ferrite sheet or card is used as a detection medium for articles to prevent theft, and a sensor capable of detecting only this sheet or card has a frequency of 200 KHz.
A sensor coil is used in which a condenser is fully connected to a primary coil that supplies a high-frequency current in the range of ~2 MHz and a secondary coil that is electromagnetically coupled to this primary coil. Alternatively: Set the resonant frequency so that when the card is brought close, it will tune to the frequency to the secondary coil.

For other metals, such as magnetic metals and non-ferrous metals, the main feature is that the tuning of the sensor coil deviates from the tuning point.

The present invention will be explained in detail below.

FIG. 1 is a schematic diagram of an embodiment of the present invention.

FIG. 2 shows its resonance characteristic diagram.

A high frequency current full-order coil CL with a frequency fr from an oscillator 1 capable of oscillating a frequency in the range of 200 KHz to 2 MHz,
supply to. A sensing coil CT, 2f, is provided so as to be electromagnetically coupled to this secondary coil CL, and a capacitor 01 is connected to this sensing coil CL2 so as to form a ULC resonance circuit.

This LC resonant circuit has a large bias of the sensing coil CL2 so that it resonates at the frequency fr when the ferrite material is brought close to the sensing coil CL2.

The number of turns and the capacity of the capacitor C1 are set.

Therefore, when the ferrite material that has been brought close is moved away from the sensing coil CL2, one frequency shifts to fo. Furthermore, when a magnetic metal or a non-ferrous metal is brought close to it, the frequency changes to fL due to attenuation due to the frequency which changes depending on its magnetic permeability and reaction due to eddy current flowing within the metal.

The frequency range of the high-frequency current supplied to the primary coil CL (
If the frequency is between 200 KHz and 2 MHz, it is possible to make full use of the unique properties of the ferrite material so that it resonates when the ferrite material approaches.

This makes it possible to obtain a detected output voltage close to the peak value. This output voltage is amplified by an amplifier 2 and output.

Note that in a region where the frequency of the high-frequency current supplied to the secondary coil CL is 200 KHz or less, the difference in high-frequency characteristics between the metal and the ferrite material cannot be clearly distinguished.

The detection output becomes unstable. On the other hand, in the region exceeding 2 MHz f, differences in characteristics can be distinguished.

It has been confirmed that the use of inexpensive recycled ferrite sheets made from industrial by-products results in a decrease in sensitivity, and that the configuration of devices such as coils and amplifiers to correct this is difficult and expensive.

An example of how this embodiment is used will be explained.

A sheet made of inexpensive recycled ferrite (thickness 0) for the book cover
．． 5 to 1 m + width 10 m + n, length 12 cm)'i, the optimum resonance point was found at approximately 600 KHz K with a coil diameter of approximately 20 α, and the value is approximately 5 times the output voltage from metal fittings such as bags. became. Of course, in actual use, this sheet will be removed from the product at the time of product purchase. To further improve detection accuracy, there is a method of installing multiple sets of sensors.

By installing it so as to cover it, approximately 10cm
It is possible to reliably detect a ferrite sheet of 15 cm and about 1 inch thick.

Note that the example in FIG. 1 is a schematic diagram of the principle, and in actual use, various compensation circuits such as a filter for removing noise components may be provided in front of the amplifier.

You can freely display all lines of the buzzer, lamp, etc. using the output of the amplifier.

As explained above, according to the present invention, the frequency is 20D.
By limiting the band from KHz to 2 MHz to achieve electromagnetic coupling between the primary coil and secondary sensing coil, and configuring the resonance phenomenon of the sensing coil and capacitor to match the high frequency characteristics of ferrite, it is possible to use only ferrite. This makes it possible to detect and provide the best salmon for theft prevention. As a result, according to the present invention, a highly accurate and highly reliable theft prevention system can be realized.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of an embodiment of the present invention, and FIG. 2 is a frequency-output characteristic diagram thereof. In the figure, 1 is an oscillator, CL is a primary coil, CL2 is a secondary sensing coil, and 2 is an amplifier. 7- Figure 1 Figure 2 LT+)Tr □Sat

Claims (1)

[Claims] 1. Includes a primary coil through which a high-frequency current in the range of approximately 200 KHz to 2 MHz flows, and a secondary sensor coil that is electromagnetically coupled to the primary coil, and changes in the electromagnetic coupling of the secondary sensor coil. An anti-theft sensor is characterized in that it detects the approach of an article to which a ferrite sheet or card is attached by detecting a change in resonance characteristics with a capacitor connected to the secondary sensor coil.