PROTECTIVE LENS FOR PHOTOCELL

United States Patent 3815968

A removable protective lens assembly for a photocell or timing light. The lens assembly can be installed in any box having a side in which a hole can be drilled. The lens assembly includes a Lexan plug threaded into an opening in the box and a filter of transluscent plexiglas supported within the plug by a retainer ring. The lens assembly prevents tampering with the photocell by vandals and filters ultra-violet rays from reaching and damaging the photocell.

05/117428

06/11/1974

02/22/1971

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Killark Electric Manufacturing Company (St. Louis, MO)

250/226

257/434, 359/350, 359/892

G01J1/04; G01J1/02; G01J1/04; G01J1/02; (IPC1-7): G02B5/20

350/1,65,318,257,287 250

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3584228	LUMINAIRE PHOTOELECTRIC CONTROL DEVICE WITH REFLECTIVE SHIELD	June 1971	Kenyon
3454323	ADAPTER FOR OPTICAL ELEMENTS	July 1969	Dierks et al.
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3351408	Sunlight-filtering ocular adapter for telescopes	November 1967	Krewalk
2506813	Light filter	May 1950	Salisbury
2442564	Device for camera or projector lenses for producing reversed images	June 1948	Heyer
2307345	Lens mount	January 1943	Zuber
2260991	Photographic lens barrel adjusting means	October 1941	Gorey

Wibert, Ronald L.

What is claimed is

1. A combination lens and filter assembly for photoelectric devices, comprising: a protective member of light-transmitting, machinable material adapted to fit into an opening and be secured there over a photoelectric device to physically protect said device, said member having a filter receiving recess on its inner side nearer the photoelectric device, a filter of material to remove rays injurious to the photoelectric device, and means to secure the filter in the recess of the protective member as an insert, whereby the filter is protected by, and held by, the protective member to form an assembly which protects the photocell from injurous rays by means of the filter and physical damage by means of the protective member.

2. The combination of claim 1, wherein the protective member is made of a plastic material, and the filter consists of a material unable to be readily worked by shaping devices.

3. The combination of claim 1 wherein the protective member is made of strong, transparent, machinable plastic, having external threads, and the means to secure the filter in the recess comprise a releasable means to hold the filter in the recess.

4. The combination of claim 1 wherein the protective member has external threads formed to fit into an opening and be secured there, and includes special wrench-engaging means by which it may be tightened and loosened within the opening only with the use of a special wrench.

5. The combination of claim 4 wherein the wrench engaging means are notches spaced around the periphery of the protective member in its outer surface.

BRIEF DESCRIPTION OF THE INVENTION

Photocells are used in a variety of applications. In many of these applications, the photocell is mounted within a box-like enclosure. A typical such application is as a timing control for utility lamps wherein the photocell is mounted within a container below a plate of glass or other transparent material to admit light to the photocell. Two difficulties have been encountered in these applications. The first difficulty is caused by the sun's light rays intersecting and damaging the photocell. The second is caused by vandals who break the lens and damage the photocell.

This invention provides a lens assembly for the container to solve both problems. The lens assembly includes a Lexan plug that is threaded into an opening in the container above the photocell. The Lexan plug is sufficiently thick to provide protection against vandals. It has special wrench grooves to permit removal of the plug for access to the photocell whereas the plug cannot be removed with conventional tools. A filter of transluscent Plexiglas is held by a snap ring within a well in the lower side of the plug. The filter is of a kind that prevents ultra-violet rays from reaching the photocell without affecting the intensity of light rays reaching the photocell.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a top plan view of the lens assembly with the photocell enclosure shown partially and with the photocell shown in dotted lines;

FIG. 2 is a view in section taken along the line 2--2 of FIG. 1;

FIG. 3 is a side elevation view of the plug;

FIG. 4 is a top plan view of the filter lens;

FIG. 5 is a side elevation view of the filter lens;

FIG. 6 is a top plan view of the snap ring retainer.

DETAILED DESCRIPTION OF THE INVENTION

This lens assembly 10 is designed for the protection of a conventional photocell 11 that is supported within an enclosure, the top wall 12 of which is shown in the drawing. The top wall 12 is provided with an internally threaded opening 13 positioned directly above the photocell 11.

The lens assembly comprises a plug 14 of transparent material, preferably Lexan No. 9034 UV. The plug 14 is about one-half inch thick and 23/4 to 3 inches in diameter. It has external threads 15 formed in its side wall that mate with the internal threads 13. There are four notches 16 in the upper surface of the plug 14 adjacent its outer wall by which the plug 14 can be tightened and loosened within the opening 13 with the use of a special wrench. Conventional tools are not effective to loosen the plug 14. A well 17 having a cylindrical side wall 18 is formed in the lower side of the plug 14. A radially outwardly extending annular groove 19 is located in the annular side wall 18. The advantage of using Lexan is that is provides structural strength against tampering and it can be machined to form the plug 14.

A filter lens 20 is sized to fit within the well 17 and is held in place by a spring metal or spring plastic snap ring 21. The snap ring 21 has hooked ends 22 and 23 which are normally separated when the snap ring assumes its normal diameter appropriate to fit within the annular groove 19. When the hooked ends 22 and 23 are grasped, they can be squeezed together for reducing the diameter of the snap ring 21 so that it can fit into the well 17 and be snapped into the annular groove 19. The filter lens is made of a material that passes light rays while filtering the ultra-violet rays. Preferably, the material is transluscent Plexiglas No. W-2067 which, although filtering the ultra-violet rays and thereby preventing them from reaching and damaging the photocell 11, does not otherwise affect the amount of light that passes through it and reaches the photocell.

The resulting lens assembly 10 is one that is easily installed to protect a photocell from tampering and from harmful ultra-violet rays. An opening 13 in the upper wall 12 of an enclosure is formed and provided with internal threads. The lens assembly 10 is assembled by positioning the filter lens 20 within the well 17 and snapping the snap ring 21 in place. Then the entire assembly is threaded into the opening 13 and tightened in place. Thereafter, the Lexan plug 14 protects the photocell 11 against tampering because the plug 14 is strong and it cannot be removed except by a special tool. The lens 20 protects the photocell 11 against ultra-violet rays.

Various changes and modifications may be made within this invention as will be readily apparent to those skilled in the art. Such changes and modifications are within the scope and teaching of this invention as defined by the claims appended hereto.