US2508700A - Sun switch - Google Patents

Description

S. WILCQX SUN SWITCH May 23, 1950 Filed May 17, 1947 i/l l ms;

IN VEN TOR.

fliemczri mlcox, agvww Patented May 23, 1950 l-JNITI'ED STATES PATENT OFFICE SUN SWITCH" Stewart Wilcox, Inglewood, CaliL';

ADDlicationMay 17, 1947, Serial No. 748,793,

7 Claims. 1

This invention relates toe, sunswitch in which an-electrical switch is operated by the presence or absence of light.

It is a primary object of this invention to provide an improved sun switch, which is more sensitive to light and which is more accurate than those heretofore proposed.

There are many instances in which it is desired to automaticallyclose electrical circuits in response to a condition of light or darkness. One important use of such a switch is to automatically control operations of isolated beacons or other unattended lights; and the like. It has heretofore been proposed to use bi-metallic strips, which are exposed to sunlight, to control operation of electrical switches, the heat from the sun causing the bi-metallic strip to open or close a switch. A difiiculty that has been encountered in such switches is the necessity of providing for variations'in the ambient temperature. Obviously, such switches are of no value if they operate only from variations in'temperature.

It has heretofore been suggested to use two metallic strips, one of which was exposed to light and the other of which was notor one of which was darkened to absorbheat from light and the other of'which was reflective, connected by suitable linkage to correct ambient temperatures. Such linkages were sometimescomplicated and sometimes not as accurate a desired. Another defect-was that most devices, as they operate on the principle of thermo-dynamics, were more affected by'brig'ht sunlight, such as at noon, and

less by reduced light,'such as sunrise and sunset.

Thuath'ere often tended to be a difference in operative efiectiveness between the various hours of-=the day." The critical periods of operation are at'sunris'e and sunset and a primary object of my' invention'isto provide a sun switch which will" be moresensit'ive at" sunrise I and sunset.

Briefly, my=switch comprises two helical bimetallic strips so connected as'to form a continuous helix. Howevenone of the strips has the high expansion metal'on the outside, while the otherhas the high expansion metal on' the inside so 'that thehelices rotate in opposite directions upon variations in temperature and this compensates-for variations in'the ambient temperature. The helix with'th'e high expansion'metal on the outside is paintedblack, or'some dark color, and exposed -to sunlight, while the'second helix is painted white, or some other light color, to reflect sunlight and} preferably, is protected by a hood whlch' providesa shaded insulatedspace around-the metallic-'- element. Preferably, the

switch-i placed'in a north-south position and the hood will extend around the second portion of the bi-metallic element, so as to protect it from sunlight.

for-it must be exposed to the sun in the early morning and late evening.

My invention will be more readily understood by reference to the drawing which forms a part hereof and inwhich Figure 1 represents an iso-' metric view of my invention and Figure 2 represents a vertical cross sectional View of 'my device.

Mounted on'a base plate I0 'is a transparent cylinder II which may be made of any suitable transparent material but which, preferably, will be made of glass. The outer end of the tube H is closed by a cap l2 which carries a bearing I 3 axially aligned with the tube. Itis preferred that an insulating and sealing gasket Id be inserted between the cap and the tube in order to make it air-tight. A bearing l 5"is also provided in the base plate and'is aligned with the first men-' tioned bearing l3,"the two bearings being adapted to receive a shaft'lfi, extending lengthwise of the tube H and to permit it to freely slide longitudinally as well as rotate therein. Also, mounted onthe base plate II] is a hood ll'spaced away from the transparent cylinder" ll, as shown; Preferably, this hood extends over the top of the cylinder when it'is placed in a horizontal position, for about half its length so as to shade the top and sides of the tube, as shown. It is'also preferred that the sides of the hood be provided with-louvers l8, as shown; The'entire assembly,

formingwhat might be called a'casing, can-be held'togetherb'y any suitable means, such as a plurality of tie rods l9;

Mounted on the shaft l6, in the interior of the transparent tube II, is a bi-metallic element, generally indicated by 20. The bi-metallic element comprises two sections 2| and 22. The first section 2! is made of a thermostatic bi-metalllc metal with the high expansion metal on the out side and is dark colored, preferably black. The

' second elementZZ is also of bi-metallic metal, but has the high expansion metal on the inside and is light colored,preferablywhite. The two sections 2 l' and 22 are rigidly secured together at the center by any'suitable means such as machine screws'23, and. at the connection are separated by a short insulator strip'24. Obviously, the two sections of the bi-metallic element should be made of the same bi-metallic material in order that their rates of expansion will be identical and b'oth'should be of the same length so that Obviously, the first portion of the "element is notshaded, at least at the sides the angle of twisting should be identical for variations in ambient temperatures. It will be obvious the first section 2! will rotate in a clockwise direction with an increase of temperature, while the second element 22 will rotate counterclockwise with an increase in temperature. One end of the bi-metallic element 20, such as the free end of the first section 2|, is rigidly attached to the cap I2, or other part of the casing, such as by screw 25. The other end of the element 20, such as the free end of the second section 22, is rigidly afiixed to the shaft l6 by any suitable means such as collar 26, to which it is aflixed, as by screw 21, the collar being rigidly mounted on the shaft l6 by any suitable means not shown. The light colored end of the helix should be arranged under the hood and the dark colored portion should be unshaded, as shown.

The shaft 16 extends through the bearing l and base plate H), as shown in Figure 2. The end of the shaft I5 is flattened, as at 30 to form a cam. Associated with the cam portion 30 of the shaft I6 is an electrical switch which is moved between open and closed position by a slight movement of a bearing member 32 which contacts the cam portion 30 on shaft l6. Many suitable switches are manufactured on the market. but one that I have found very satisfactory is a Micro pin-type switch which is actuated by movement of the bearing member of .0003 inch. In a neutral position the bearing member 32 will contact the flat portion of the cam 30, in which case, customarily, it will be preferred that the switch be open. It will. be obvious that as the adsorption of heat from light twists the bi-metallic element thereby rotating the shaft IS, the hearing member 32 of the switch 3! will be moved by rotation of the shaft to close the switch 3!.

Enclosing the switch 3! and cam is a casing which preferably is tapped and threaded as at 4| to receive an electrical conduit, not shown. The cap 4!) can be removably attached to the base plate It! by any suitable means such as studs 42. In some installations it may be preferred to place an insulating plate 43 within the cap 40 and to attach electrical binding posts 44 and 45 thereto. These binding posts are adapted to receive the ends of electrical power lines, not shown. The switch is connected to the binding posts by spring members 46 and 41 which, when the cap and base plate are assembled engage the binding posts 44 and 45, respectively. Thus the binding posts 44 and 45 can be connected to suitable power leads while the cap is removed from the base plate. Then when the base plate H! and cap 40 are as sembled there is an automatic connection to the switch 4! through the spring contacts 46 and 41. It is believed that operation of my sun switch will be obvious. In the absence of sunlight the ambient temperature enclosing both sections of the bi-metallic element will be the same and the shaft Hi will be in a neutral position regardless of the ambient temperature. This is due to the fact that as the two sections of the oi-metallic element are of the same length, and have the same coeiiicient of expansion, but operate in opposite directions. ambient temperature changes thus will rotate the two sections equally in opposite directions, thereby neutralizing their rotational effect. Any expansion of the metals can exert a force in a longitudinal direction without changing the setting of the switch 42. However. when the sun shines upon the first section 2| of the bi-metallic element its darkened color adsorbs heat from the light. As the other section '22 of the bi-metallic element is both shaded and darkened the light will have no effect upon the second section. Thus the total effect of the bimetallic element will be to rotate it through a slight angle, which rotates the shaft [6 and its cam 30, thereby moving the pin 32 of the switch 3|. With the passing of the light the first section will cool relative to the second and rotate the shaft and cam 30 in a backward direction to again present the flattened surface 30 to the pusher rod 32.

It will be obvious to those skilled in the art that various modifications of my invention can be made without departing from the spirit and scope thereof. Accordingly, the appended claims are to be given a construction commensurate with the scope thereof and as broad as is permitted by prior art.

I claim:

1. A sun switch comprising a casing having a. transparent portion, a helical bi-metallic element of relatively small diameter in the transparent portion, one end of which has the high expansion side outside and the other side of which has the 5 high expansion on the inside of the helix, one

end of said helix being painted white and the other painted black, a rotatable and longitudinally displaceable shaft journaled in said casing, one end of said bi-metallic element being affixed to said casing and the other end of said bimetallic element being affixed to said shaft, a cam carried by said shaft and a switch operated by said cam.

2. The apparatus of claim 1 comprising also a hood shading the white portion of said bi-metallic element.

3. The apparatus of claim 1 comprising also an insulator separating the two ends of said helix.

4. A sun switch comprising a base plate, a transparent cylinder afiixed to said base plate, a cap on said transparent cylinder, a rotatable and longitudinally displaceable shaft axially aligned in said transparent cylinder, a two-sectioned helical bi-metallic element co-axially aligned with said shaft, one section of which has the high expansion side outside and the other section of which has the high expansion on the inside of the helix, one section of said helix being painted white and the other painted black, one end of said bi-metallic element being afflxed to said shaft and the other end thereof being rigidly secured with re spect to said base plate, a cam carried by said shaft and a switch operated by said cam.

5. A sun switch comprising a transparent casing, a helical bi-metallic element within said transparent casing, one end of which has the high expansion side outside and the other side of which has the high expansion on the inside of the helix, one end of said helix being light colored and the other dark colored, a hood superposed over the light portion of said bi-metallic element, one end of said helix being rigidly secured to said base casing, a longitudinally displaceable shaft keyed to the other end of said bi-metallic element, a cam carried by said shaft and a switch operated by said cam.

6. A sun switch comprising a casing having a transparent portion, a helical bi-metallic element within the transparent portion of said casing, one end of which has the high expansion side outside and the other side of which has the high expansion on the inside of the helix, one end of said helix being light colored and the other dark colored, a longitudinally displaceable cam keyed to one end of said bi-metallic element, the other end of said helix being rigidly secured to said casing and a switch operated by said cam.

7. A sun switch comprising a base plate, a transparent casing afiixed to said base plate, a, rotatable and longitudinally displaceable shaft axially aligned in said transparent casing, a twosectioned helical bi-metallic element in said casing coam'ally aligned with said shaft, the two sections being of equal length and equal coefficient of expansion, the first section of said element being painted black and having the high expansion side outside and the second section of said element being painted white and having the high expansion side on the inside of the helix, means aflixing one end of said element to said shaft, 15

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,461,523 Fransson July 10, 1923 1,641,170 Karlson Sept. 6, 1927

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