US3882363A

US3882363A - Photocontrol with automatic light operated reset

Info

Publication number: US3882363A
Application number: US448861A
Authority: US
Inventors: John J Misencik
Original assignee: Westinghouse Electric Corp
Current assignee: Hubbell Inc
Priority date: 1974-03-07
Filing date: 1974-03-07
Publication date: 1975-05-06
Anticipated expiration: 1992-05-06

Abstract

A photocontrol is provided with manual interruption and automatic reset. In the photocontrol, a photosensitive resistor controls operation of a thermal switch which in turn controls power to a load. The load circuit is manually interrupted when a spring-loaded actuator is lodged between the thermal switch contacts. Reset is obtained when ambient light rises above a predetermined level and causes the thermal switch to deflect thereby releasing the actuator which is forced by a spring to its original position. The thermal switch contacts are then free to open and close in response to the rise and fall of ambient light level.

Description

O United States Patent 1 [111 3,882,363 Misencik May 6, 1975 4] PHOTOCONTROL WITH AUTOMATIC 3,416,117 12/1968 Grosse-Brauckmann 337/358 LIGHT OPERATED RESET [75] Inventor: John J. Misencik, Shelton, Conn. 52 j H T If orney, gen 0r zrme er [73] Assignee: Westinghouse Electric Corporation,

Pittsburgh, Pa. [57] ABSTRACT 22 F'] d: Mar.7 1974 1 1e A photocontrol is provided with manual interruption PP N05 448,861 and automatic reset. In the photocontrol, a photosensitive resistor controls operation of a thermal switch 52 US. Cl. 317/124- 219/502- 337/73- which tum comm Power a The 337/258 cuit is manually interrupted when a spring-loaded ac- 51 Int. Cl. HOlh 47/24 that is lodged between the thermal Switch Contacts [58] Field of Search u 219/502; 317/124; 337/3, Reset is obtained when amblent light rises above a 337/13 70 72 356 358 73 predetermined level and causes the thermal switch to deflect thereby releasing the actuator which is forced [56] References Cited by a spring to its original position. The thermal switch contacts are then free to open and close in response to UNITED STATES PATENTS the rise and fall of ambient light level. 2,875,348 2/1959 Kazan 219/502 X 3,048,833 8/1962 Bernheim 317/124 X 7 Claims, 3 Drawing Figures LIGHT g;

IO POWER SUPPLY LOAD r60 PHOTOCONTROL WITH AUTOMATIC LIGHT OPERATED RESET BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to photocontrol systems and more particularly to automatic resetting light sensitive switches.

2. Description of the Prior Art Photocontrol devices are well known in the art and are widely used in automatic control applications. Prior photocontrols generally employ a photosensitive resistor in combination with a current-sensitive or heatsensitive switching element to operate a circuit when the illumination level falls or rises. Typically, as ambient light rises above a specified level, the photosensitive resistor passes current in response to incident light which actuates a relay or an electronic switch. Alternatively, the current output is used to excite a heat generator, such as a carbon resistor, which in turn actuates a thermal switch. Then as ambient light falls below a specified level the switching element is de-energized and the control cycle is completed.

Such prior art arrangements are adequate for applications which require the load to be energized throughout the entire period of darkness, as for example, where streetlights are required to be on all night for safety purposes. But for other applications, such as home lighting systems, it is desirable for reasons of conveniencc and economy as well as safety to be able to manually interrupt the energized load at will before it is switched off automatically. This, of course, could be accomplished in conventional photocontrolled switch arrangements by utilizing an auxiliary switch in series with the load. but would necessarily defeat the automatic operation of the photocontrol.

Therefore, there is needed a simple photocontrolled switch which may be manually interrupted at will, and which will reset after being manually interrupted.

By way of further background, reference may be made to Kazan US. Pat. No. 2,875,348. Feb. 24, 1959. for a description of a thermal switch assembly of the general type to which the present invention applies. However, no prior art photocontrol is known with the automatic reset function provided by this invention.

SUMMARY OF THE INVENTION The present invention provides flexibility in the operation of photocontrolled switches. Despite the utility of prior art switches as mentioned above, it is desirable in certain applications to be able to manually disable the photocontrolled switch in such a manner that it will automatically reset in response to change in light level. Accordingly, the principal object of this invention is to provide a photocontrolled switch with simple means for interrupting the control sequence and with simple means for automatic resetting to photocontrolled operation in response to change in light level.

The invention provides these advantages in a system which includes a source of electrical power, an electrical load, and an electrical circuit which transfers power from the source to the load. Power is transferred in photocontrolled operation when illumination, which alternately increases and decreases with the passage of time, falls below a predetermined level. Means are provided for opening and closing the power transfer circuit indefinitely and without human supervision such that the power transfer circuit is closed as the illumination falls below a predetermined level and is opened as the illumination rises above the predetermined level. Manual interruption means are provided for opening the power transfer circuit and causing it to remain in circuit open condition during the period that the illumination remains below the predetermined level. Means are provided for automatic reset to photocontrolled operation such that the manual interruption means become disabled as the illumination rises above the predetermined level, thereby allowing the power transfer circuit to return to circuit closed condition without human supervision as the illumination subsequently falls below the predetermined level.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an elevation view, in section, of a preferred embodiment of the invention, including a schematic representation of a circuit in which it may be employed.

FIG. 2 is an enlarged view ofa portion of FIG. 1 illustrating a manually operated mechanical actuator.

FIG. 3 illustrates a second embodiment of a manually operated mechanical actuator.

DESCRIPTION OF THE PREFERRED EMBODIMENT Throughout the description which follows like reference characters refer to like elements on all Figures of the drawing.

A preferred embodiment of the present invention is illustrated in FIG. 1 which shows a photosensitive device 20 connected in series electrical circuit relationship with a power supply 10 and a heat generating resistor 31. Heat generated in the resistor 31, which is controlled by the light received by photosensitive device 20, is utilized to operate a thermal switch 30 for controlling the power transferred from the power supply 10 to a load 60. When the light, indicated by arrows 21, impinging upon the photosensitive device 20 reaches a certain predetermined level, the thermal switch 30 closes an electrical circuit and current flows from power supply 10 through the photosensitive device 20 and the heat generating resistor 31 and back to the power supply 10.

The photosensitive device 20 is arranged to receive light from a specified source whose intensity alternately increases and decreases with the passage of time. In order to control the operation of a thermal switch 30, photosensitive device 20 passes current from power supply 10 to heater resistor 31 when incident light exceeds a predetermined level. In its ideal configuration photosensitive device 20 has infinite resistance to the flow of current in the absence of incident light and zero resistance in the presence of a predetermined level of light. It should be understood that while these limits may not be realizable in practice, the required function may be satisfied by a conventional cadmium sulfide photocell which exhibits relatively small resistance in the presence of light and relatively large resistance in the absence of light.

The thermal switch assembly 30 includes a heater resistor 31 which is disposed in a thermally coupled relationship with a bimetal strip 32, which is designed to flex in response to heat. The switch assembly 30 comprises a stationary contact 34 and a contact 33 carried by the bimetal strip 32. The

contacts

34 and 33 are opened and closed by the flexing of the bimetal strip 32 to connect or disconnect the load 60 with the power supply 10.

The bimetal strip 32 is arranged in cantilever fashion with one end attached to a housing 50 while the other end carries the electrical contact 33 and a latching portion 35. The first electrical contact 33 is carried by the bimetal strip 32 and is disposed to engage the second electrical contact 34, the second electrical contact 34 being mounted on the housing 50.

A heater resistor 31 is connected in parallel circuit relationship with the load 60 and both the heater resistor 31 and the load 60 are energized by the power supply 10. This apparatus is operative without regard to the magnitude or character of the load 60, but the heater resistor 31 must be of relatively high resistance to generate sufficient heat from the available control current to cause the bimetal strip 32 to flex and operate the

contacts

33 and 34. Further. the current rating of the photosensitive device 20 should exceed the maximum current required by the heater resistor 31 to actuate the bimetal strip 32.

During normal photocontrolled operation the predetermined light level is detected by the photosensitive device 20 which passes current from the power supply in response to the incident light. As light received by photosensitive device increases, the resistance of photosensitive device 20 diminishes thereby allowing greater current flow through the heater resistor 31. In-

creased current flow through the heater resistor 31 generates heat which causes the temperature of thermally coupled bimetal strip 32 to rise. When actuating temperature which corresponds to the predetermined light level is reached the bimetal strip 32 bends away from heater resistor 31, and in doing so disengages contact 33 from contact 34 thus deenergizing load 60. As the light level subsequently decreases, the resistance of photosensitive device 20 increases to the point that sufficient current is no longer passed to heater resistor 31 to maintain the bimetal strip 32 above its actuating temperature; thus. contact 33 is moved by the bimetal strip 32 as it relaxes to engage contact 34 and thus load 60 is energized. This sequence is repeated indefinitely as the illumination received by the photosensitive device 20 alternately increases and decreases about the predetermined reference level. It should be noted that because of the time required to heat the bimetal strip 32 to actuating temperature and for the bimetal strip 32 to deflect away or move toward the heater resistor 31, the photocontrol will respond only to light levels which are sustained above or below the predetermined level for a period of time greater than the switching time of the bimetal strip 32. Thus light fluctuations which occur more rapidly will have no effect on the photocontrol.

A manually operable mechanical actuator assembly is provided for opening the

contacts

33 and 34 at any desired time, and the actuator 44 locks the contacts in open circuit position until the level of the light received by the photocontrol device 21 reaches a predetermined level. When the light reaches the predetermined level the actuator 44 is returned to its original, or non-locking position.

The mechanical actuator assembly 40 includes a coiled spring 42 which is attached to housing 50 and surrounds an actuating arm 43 of a pushbutton 41. The housing 50 aligns the actuator 44 with the latching portion 35 of the bimetal strip 32 so that the latching portion 35 of the bimetal strip 32 engages the actuator 44 tor 44 and the latching portion 35 are both nonconducting members fashioned from suitable insulating material.

in photocontrolled operation actuator 44 is fully retracted against housing 50 and makes no physical contact with bimetal strip 32 or latching member 35 so that

contacts

33, 34 may open and close freely in response to the received light level. However. when it is desired to override normal photocontrolled operation, actuator 44 is manually positioned between housing 50 and bimetal strip 32 by pushing on the pushbutton 41 until the latching portion 35 interlocks with actuator cavity 45. In this position of the actuator 44 the

contacts

33, 34 are held in circuit open position and load 60 is de-energized. The actuator 44 is held in place between latching portion 35 and housing 50 by the compressive force exerted by the bimetal strip 32 as it is displaced from its relaxed, circuit closed position. In this position of the actuator 44, the coiled spring 42 is fully compressed and exerts a constant retracting force against the pushbutton 41 which lies flush within the actuator recess 52 of housing 50, but is not strong enough to overcome the binding force exerted by bimetal strip 32 as it holds actuator 44 in its interlocked position with latching portion 35.

Interruption of the circuit to the load 60 is maintained until such time as light received by the photosensitive device 20 rises to a level sufficient to cause the heat generating resistor 31 to generate heat which in turn causes the bimetal strip 32 to flex upward and disengage the latching portion 35 from the cavity 45 in the actuator 44. The compressive force exerted by bimetal strip 32 against the actuator 44 diminishes as the bimetal strip 32 is heated to actuating temperature. Automatic reset is obtained when the bimetal strip 32 deflects away from the heater resistor 31 and latching portion 35 is lifted out of the actuator cavity 45 thus allowing the coiled spring 42 to force the actuator 44 to its fully retracted position. While the actuator 44 rests in its fully retracted position.

thermal switch contacts

33, 34 open and close without interference according to the rise and fall of ambient light received by the photosensitive device 20.

In FIG. 3 a second embodiment of a manually operated actuator assembly 40 is illustrated. This configuration is distinguished by the construction of a pushbutton 41 which eliminates the need for the coiled spring 42 shown in FIG. 2. Here, the pushbutton 41 is generally cylindrical in form and lies within a cylindrical recess 52. Pushbutton 41 has sufficient mass to move the actuator 44 to its fully retracted position solely by the force of gravity when the photocontrol is installed with the actuator assembly 40 arranged in an upright posi rupted, the actuator 44 is held in place between the,

latching portion 35 and the housing 50 by the compressive force exerted by the bimetal strip 32. In this position of the actuator 44, the mass of pushbutton 41 exerts a constant retracting force against the actuator 44, but is not strong enough to overcome the binding force exerted by the bimetal strip 32 as it holds the actuator 44 in its interlocked position with the latching portion 35. The retracting force of gravity exerted against the mass of pushbutton 41 is, however. sufficient to overcome the frictional forces exerted by the walls of housing channel 51 against actuator arm 43 and of actuator recess 52 against the surface of the cylindrical pushbutton 41 so that the actuator 44 is moved to its fully retracted position by the force of gravity as latching portion 35 is lifted out of the actuator cavity 45.

While there has been shown and described what is at present considered to be the preferred embodiment of the invention, modifications thereto will readily occur to those skilled in the art. It is not desired, therefore, that the invention be limited to the specific arrangement shown and described.

I claim:

1. A photocontrol comprising:

a photosensitive device which passes current when excited by a predetermined light level;

a heat generator which is energized by said photosensitive device;

a bimetal member which moves in response to heat received from said heat generator;

a pair of electrical contacts, one of said contacts being carried by said bimetal member, said contact carried by said bimetal member being moved when light received by said photosensitive device falls below a predetermined level to engage said other electrical contact to close an electrical circuit including a power source and moves when light received by said photosensitive device rises above a predetermined level to disengage said other electrical contact to open said electrical circuit; and

means for locking said pair of contacts in circuit open position, said means being actuated by a predetermined light level to permit said contacts to move to circuit closed position.

2. The photocontrol of claim 1 wherein said means for locking said contacts comprises:

an actuator having a latching portion which is movable to a first position in which said pair of electrical contacts are free to open or close according to the rise or fall of the light level, said actuator being movable to a second position in which said actuator latching portion interlocks with said bimetal member causing said pair of contacts to be held in circuit open position; and

means for releasing said actuator from the second position when light received by said photosensitive device rises above a predetermined level.

3. The photocontrol of claim 2 wherein the means for moving said actuator from the first position to the second position comprises a pushbutton affixed to the free end of said actuator.

4. The photocontrol of claim 2 including means for moving said actuator to said first position after said actuator has been released by said predetermined light level received by said photosensitive device.

5. The photocontrol of claim 4 wherein the means for moving said actuator from the second position to the first position comprises a resilent member affixed to the free end of said actuator which deforms as said actuator moves to the second position, said resilient member being adapted to urge said actuator to the first position as said resilient member recovers its original shape.

6. The photocontrol of claim 5 wherein said resilient member comprises a coiled spring.

7. The photocontrol of claim 4 wherein the means for moving said actuator from the second position to the first position comprises an actuator having sufficient mass to move said actuator to its first position by the force of gravity after said actuator has been released by said predetermined light level received by said photosensitive device.

Claims

1. A photocontrol comprising: a photosensitive device which passes current when excited by a predetermined light level; a heat generator which is energized by said photosensitive device; a bimetal member which moves in response to heat received from said heat generator; a pair of electrical contacts, one of said contacts being carried by said bimetal member, said contact carried by said bimetal member being moved when light received by said photosensitive device falls below a predetermined level to engage said other electrical contact to close an electrical circuit including a power source and moves when light received by said photosensitive device rises above a predetermined level to disengage said other electrical contact to open said electrical circuit; and means for locking said pair of contacts in circuit open position, said means being actuated by a predetermined light level to permit said contacts to move to circuit closed position.

2. The photocontrol of claim 1 wherein said means for locking said contacts comprises: an actuator having a latching portion which is movable to a first position in which said pair of electrical contacts are free to open or close according to the rise or fall of the light level, said actuator being movable to a second position in which said actuator latching portion interlocks with said bimetal member causing said pair of contacts to be held in circuit open position; and means for releasing said actuator from the second position when light received by said photosensitive device rises above a predetermined level.