Communications: electrical – Condition responsive indicating system – Specific condition
Patent
1981-02-07
1983-05-17
Swann, III, Glen R.
Communications: electrical
Condition responsive indicating system
Specific condition
250216, 340550, G08B 1318
Patent
active
043842801
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to an anti-entry device for surfaces in which the edge of the surface to be protected is provided with light-reflecting layers which conduct light coming from a source of light to a receiver, said receiver being connected to an alarm which is activated when the light to the receiver is disturbed.
An anti-entry device of the above generally described type is disclosed in West German Patent 23 53 702. The light-reflecting layers in that anti-entry device are disclosed as flat mirror surfaces which are arranged in a sandwich system, for instance between the panes of a window. In this system, the adjustment requirements are minor since the window panes totally reflect light which deviates from the vertical and thus direct it again onto the mirror surfaces.
The expense for adjustment becomes, however, incomparably greater when the anti-entry device is used to secure unglazed surfaces, since the reflected light is reflected by twice the angle of the mirror surface. Therefore even small errors in either the angle between the mirror surfaces or the lateral displacement of the mirror surfaces have a very detrimental effect on the intensity of the light received.
BRIEF SUMMARY OF THE INVENTION
The object of the present invention is to provide an anti-entry device of the above-described type which while being capable of various applications, results in practically no problems in adjustment and is economically produced.
This object is achieved in accordance with the present invention by forming the light-reflecting layers such that they reflect an impinging beam of light, regardless of its angular position in the plane extending between the layers, parallel to its direction of incidence.
In this way any errors in the angle between the light-reflecting elements do not have a detrimental effect on the intensity of the light received and thus on the sensitivity of the anti-entry device. Accordingly the expense for the adjustment of the mounting position of the anti-entry device is kept at a minimum.
It is preferred to form the light-reflecting layers of prismatic elements along opposite edges of the surface to be protected. In order to keep the materials and cost of assembly as low as possible, each light-reflecting layer comprises a mirror strip of optically transparent material, said strip consisting of a plurality of parallel furrows which extend the length of the strip, each furrow having the form of a 90.degree. prism. In this manner a beam of light which penetrates the base surface of a prism is reflected back by the side surfaces in its direction of incidence and parallel thereto, in the plane extending between the strips.
It is also possible to form the light-reflecting layers of 90.degree. angle mirrors. In this case it is advantageous to form the light-reflecting layers of a mirror strip which consists of a plurality of furrows extending parallel to each other and to the longitudinal direction, each furrow forming a 90.degree. angle mirror. Although it is preferred that the mirror strips consist of a material which is highly reflective they may also consist of other materials which are easier to work and less reflective, for instance plastic, the surfaces of which serve for the reflection of the light being mirrored.
In the case of the anti-entry device of the invention, a light-emitting diode operating in the infrared region is preferably used as a source of light. This source of light is modulated. The change in the phase relationship between the entering signal and the received signal can be used to actuate the alarm. It is also possible to use a change in intensity of the received signal in order to activate the alarm.
The present specification is concerned throughout with light which is directed from a source by the light-reflecting layers to a receiver. The expression light is to be understood in this connection as a generic concept for electromagnetic radiation, i.e. electromagnetic radiation of any wavelength.
The anti-entry device of the inv
REFERENCES:
patent: 4107522 (1978-08-01), Walter
patent: 4239961 (1980-12-01), Lasar
patent: 4310836 (1982-01-01), Stanzani
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