US2198725A - Alarm system - Google Patents

Description

ALARM SYSTEM Philip N. Smith, Melrose Highlands, Mass., as-

signor to Hammond V. Hayes, Boston, Mass.

Application December 9, 1937, Serial No. 178,940

Claims. (Cl. Z50-83) UNITED STATE The present invention relates to alarm sysrect optical communication with the detector.

tems, and more particularly to systems of the general type disclosed in my prior application, Serial No. 118,747, filed January 2, 1937.

5 The system described in my prior application makes use of a. radiant energy detector sensitive to changes of radiant energy at any point with in a wide angle iield ci vision, and capable of operating a suitable alarm upon the occurrence 1g of an abnormal condition, such as the presence of a fire or a burglar within the space to be protected. The detector is responsive, not to the total energy -falling thereon, vbut rather to changes or modulations of energy, and for thatv reason its usefulness in detecting an abnormal condition depends on the amplitude and rapidity by which a change of. energy is produced by the occurrence of the abnormal condition.

Considering burglar detection as a specific ex' ample, it is usually impossible for a person to step into the iield of vision of the instrument, or even to move about Within the field, without causing a sufficient modulation of radiant energy to actuate the signal. It is, however, conceivable that at distances representing substantially the limit of sensitivity of the detector, a burglar who has somehow succeeded in getting himself placed within the field might move about in such a man-1 ner that any changes of energy would be insufcicnt in amplitude, or insufficiently sudden, to

actuate the ale rm. This condition would not ordinarily arise. except in a moderately open space, since if any obstructions, such as furniture, machinery and the like were present, any eiiective movements into or out oi the spaces behindthe obstructions would result in sufficient changes in the energy impinging on the receiver.

The principal object of the present invention is to provide improvements in the alarm systems [n of this 4general type, with a particular view towa rd increasing the certainty of operation under such conditions as are mentioned above.

With this object in view, the present invention contemplates the provision of means used in conjunction with a radiant energy receiver for insuring that suitable modulation of the energy shall occur upon movements of the abnormal condition" with the space to be protected. In its prcferrcd,form the invention provides a screen or grating whereby the eld of vision of the detector is broken up into adjacent lzones of relatively small size. Some of the zones, which may be designated insensitive or'shadowzones, are 4 blocked olf from optical relation with respect tov the detector, while the intervening zones are in di- These several zones or bands are of such size that it is impossible for a person to move about effectively without Vstepping from a shadow zone into a sensitive zone and 'vice versa, whereby the 5 necessary changes of radiant energy are effected. Although the invention is not limited to any particular form of detector, it is preferred' to use the detector described in my prior application, which is of the type described in the patent to Hayes 10 1,954.204, dated April 10, 1934, and the patent to William M. Hall No. 2,115,578, dated April 26, 1938, involving the use of a dark heat-absorbing substance. This detector is advantageous, not

only because of its extreme sensitivity, but also- 15 because it is actuated by energy emitted from the abnormal condition itself, and is 'therefore independent of any constant or gradually variable sources of radiant energy (lamps, radiators, etc.) normally existing within the field of vision. 20

In the accompanying drawing Fig. l is a plan view of the apparatus; Fig.2 is an elevation partly in section of the preferred receiving instrument; and Fig. 3 is a perspective view showing the setting of the apparatus in a corner of the 2 5 space to be protected.

As shown in Fig. 2, the preferred instrument, which is exactly similar to that shown in my copending application, comprises a uif chamber 4 containing a body of radiant energy absorb- 30 ing material. The chamber 4 is enclosed by a window S and in tack of the chamber there is provided a diaphragm which is actua-ted by any changes in gas pressure occasioned by a sudden variation of radiant energy imp-inging on the dark 35 substance. In front of the window 6 there is .provided a lons system diagrammatically shown as a simple lens 8 to focus radiant energy from any part of the wide-angle field of vision on the dark substance. The window and lens are of 40 rock salt or other material transparent to infra .to give a signal or alarm.

f The instruent is mounted at the corner of a cage l0 of quadrantal form. The cage is made 520 up of top and bottom walls l2, each in the shape of a quadrant, and side walls i3; the Whole being arranged to it in the upper corner of a room as shown in Fig. 3. The front of the cage comprises a grating consisting of a series of vertical 55 i scured; next penumbras" 2U from which theV and finally,`

slats `IG connected between the top and bottom Walls- As indicated in Fig. 1, the slats block oi por- .tions of the eld' of vision of the detector, thus breaking up the whole eld of vision into a succession of radiating Zones: first, shadow zones I9 from which the detector is completely obor laway from the' instrument without bringing a part of his body from a light zone to 'a shadow zone, or vice versa, whereupon the detector is suiiiciently inuenced by thel resulting change of energy to actuate the alarm.

In order that changes of radiant energy may beA a's sudden as possible upon the movement of a person through the field of vision, the penumbra zones should. be as narrow as possible with relation to the shadow and sensitive zones. For this purpose it is desirable that the slats should be somewhat wider thanthe diameter of the lens. As an example of a construction which'has been found satisfactory, the radius o the quadrant cage is approximately ten inches, the lens diameter is vone-half inch, and the slats are seveneighths of an inch wide, the spaces between the slats being also about seven-eighths of an inch.

Furthermore, the width of the shadow zone at the distance corresponding to the limit of sensitivity should not be so wide that a person could remain entirely therein. The dimensions given in the above example have been found suitable for detection at distances up to 20 or 30 feet from the instrument. For greater coverage, two or more instruments may be used; in fact, even for small spaces, the use of two instruments at oppol site corners isA desirable, not only for coverage of the spaces directly beneath the cages, but also .to

give an overlapping of the light and shadow zones of the separate instruments.

The material of which the slats are made is not ordinarily of importance, so long as they are opaque to infra-red energy. They may be of Wood or metal, or even glass, since the latter is opaque to the longer infra-red and hence serves to divide the eld of vision into Zones, some of which are in optical communication with the receiver and some of which are obscured there? from. In fact, the use of glass, which is transparent to visible light but opaque to the longer infra-red, is advantageous in a system for more complete protection; the receiver, which is responsive to visible light, as well as to infra-red, will then be actuated by any change of visible light at any point within the Whole eld, as by the breaking out of a re or the turning on of a ashlight, and will also be actuated by the modulated infra-red energy caused by the movement of a low temperature source (a burglar. for example) through the zonformed bythe slats.

Although a speciic embodiment has been shown and described, it -will be understood that the invention is not thus limited, but may be considerably varied. For example, it is not necessary that the slats should be vertical, although they should f preferably be arranged so that 'a person would be more likely to move across, rather than along, the zones formedtheresy; in Ysome instances, a's

tionary grating in front of the receiver and having slats of material transparent to visible light 10 in the protection of sairways, theslats might sitive to changes of radiant energy, and a staand substantially opaque vto infra-red energy,

forming zones which for infra-red are in optical communication with and obscured from the receiver.

3. An alarm device comprising a receiver responsive to changes in infra-red energy impingng thereon and adapted te receive energy radiated indiscriminately from sources within a space to be protected, and stationary screening means in front of the receiver to divide the eld of vision of the receiver into z :es which are respectively.

in communication vvitlY` "ne receiver and obscured therefrom to insure mocuiation of energy impinging on'tne receiver from a source moving within said space.

4. An alarm device cemprising a receiver responsive to changes in visible and infra'red energy impinging thereon and adapted to receive energy radiated indiscriminately from sources within a space to be protected, and stationary screening means having members of material transparent to visible light and substantially opaque to portions of the infra-red spectrum, said members being placed in front of the receiver to form zones which for infra-red are respectively in communication with the receiver and obscured therefrom to insure modulation of infra-red energy impinging on the receiver from a source moving within said space.

5. An alarm device having a body of material sensitive to changes in radiant energy, and stationary screening means in front of the window having members with dimensions at least as great as those of the body of sensitive material to form within the eld of vision-zones vwhich are respectively in communication' .with and obscured from the receiver.

PHILIP N. SMlTH.

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