Abstract:
The present invention is a thermally activated electrical switch for use in simulating human activity. The invention is features dual heat sources enclosed in a thermally isolated chamber within the invention. Since the activation of the switch is dependent upon the ambient temperature of the environment, it opens and closes at sufficiently random intervals to simulate human activity. Other embodiments include the use of photoelectric sensors and timers to further vary timing of the switch actuation.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS AND PATENTS 
     This Application claims priority based on prior Provisional Application No. 60/521,104, filed Feb. 21, 2004, which is incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to the field of electrical security timers and more particularly relates to a randomized timer that is thermally operated. 
     BACKGROUND OF THE INVENTION 
     Over the past 40 years, consumers, for the purpose of home security, have purchased millions of automatic switches, manufactured by several major manufacturers. More specifically, for the purpose of simulating human activity in dwellings and other buildings to deter burglars when the occupants of the dwelling or building are away. Typical switches are clock operated. All of these clock-operated switches are settable to turn the light on or off, either on the hour or the half hour, two or more times in a 24-hour period. This practice of using a timer has become so widespread that it has become common knowledge that if the lights in a house switch on or off on the hour or the half hour, or at the same time on successive nights, that this is an indication that the owners are away and the house is unoccupied, indicating that a timer is being used to simulate occupancy. Even the popular movie of the late 1990&#39;s, entitled “Home Alone” has as a theme, the burglars who checked the time that the lights came on to determine that the owners were away on vacation. 
     The predictability of the timing of these devices has rendered them virtually counter-productive as burglar deterrents, as they now serve as much to inform the burglars of the absence of the occupants. In addition to the electromechanical clock types described, solid-state equivalent units are also available, also having the same inadequacies as the electromechanical types, for the purpose intended. 
     Notwithstanding their obsolescence as effective burglar deterrents due to their well known predictability, still they are continuously sold in all department stores, hardware stores, chain stores, discount stores and variety stores throughout North America, because no preferred alternative has been made available. It is the purpose of this invention therefore, to make available such alternative to better fill the need. 
     All clock operated timers and also the solid-state equivalent types, have three functional inadequacies, which prevent them from being effective burglar deterrents. First, they are precisely predictable, because they operate at the same times, day after day. Second, they are vulnerable to power interruptions, which gets them “off-schedule” until manually reset by the owner, who may be away for days or weeks, or in the case of a vacation home, they can be off-schedule for months. Third, the setting of time of day, and programming the turning on and off of the lights is time consuming, complicated, and bothersome. 
     The present invention overcomes all three of the above inadequacies, as will be explained herein below. The present invention described herein controls the lights in a way that is completely unrelated to horological time. The present invention will never, or very rarely if ever, turn its load on or off at the same time as the previous day. The present invention is so unlikely to turn its load on or off at the same time as the previous day, that it is estimated by probability at one chance in approximately 500,000. 
     Second, because the present invention has no relationship to the horological clock, and has no horological schedule. Therefore, after a power interruption, and when the power is restored, the present invention continues turning its load on and off at intervals unrelated to horological timing, and therefore continues to serve the intended purpose just as effectively as if the power interruption had not occurred. Third, the present invention eliminates the need for any setting of time of day and time-of-operation programming. In contrast, a single switch, set to “security” position in an instant, is all that is needed to enable the invention to function for its intended purpose. 
     The invention herein described is designed to be useful in three different embodiments as herein below described. In its basic simplest form, the user simply turns this invention on or off by a single manual switch. The invention may also be combined with a photoelectric sensor, which is well known in the art. In this embodiment the invention functions during the night, but not during the day. The invention may also be combined with a clock-operated switch, well known in the art, so as to function within selected hours only. In all three of the above embodiments the invention can be configured to plug directly into the wall outlet of the home, or fitted with a power cord and plug, and placed on any convenient table. It is available, therefore, as either “wall models” or “table models” for the convenience and preference of the user. 
     It is recognized, that the switching on and off of lamps, radios, and the like by electromechanical or electro-thermal means, as well as the timing of such switching, can be duplicated by solid state electronic means, using integrated circuits, triacs and other solid-state components. The duplication of the results of the invention by solid-state electronic means should be considered as the use of the present invention. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing disadvantages inherent in the known types of security switches this invention provides an improved thermally activated security switch. As such, the present invention&#39;s general purpose is to provide a new and improved security switch that will operate independently from horological time. 
     The present invention is a thermally activated device for the simulation of human activity in an unoccupied dwelling. In its most basic embodiment, the invention utilizes a thermally sensitive switch, which when in use is electrically connected to a standard household electrical receptacle. Two heat sources are adjacent the switch, a primary and secondary resistor. Secondary resistor is connected to the electrical source in a parallel relation to the switch, while the primary, and significantly larger, resistor is in series in relation to the switch, so that it is activated only when the switch is closed. Both resistors and the switch are housed in a thermally insulating switch housing, which is in turn housed within an exterior housing. Exterior housing features an electrical receptacle, an electrical interface and a primary bypass switch, allowing a user to bypass the thermal switch and maintain a continuous electrical current between the interface and receptacle. 
     In use, the device is plugged into a receptacle and a load, such as a lamp or television set, is plugged into the device&#39;s receptacle. For everyday use, the primary switch is left in a continuous “on” position, electrically bypassing the thermal switch. For security use, the primary bypass switch directs current to the thermal switch. Usually, the thermal switch is closed, but as the resistors raise the surrounding temperature in the thermally insulated housing, the thermal switch is opened. The surrounding temperature drops slowly as secondary resistor is still providing heat and the thermally insulated housing slows heat transfer away from the switch. Eventually, the temperature cools to the point that the thermal switch again closes and allows current through. 
     The more important features of the invention have thus been outlined in order that the more detailed description that follows may be better understood and in order that the present contribution to the art may better be appreciated. Additional features of the invention will be described hereinafter and will form the subject matter of the claims that follow. 
     Many objects of this invention will appear from the following description and appended claims, reference being made to the accompanying drawings forming a part of this specification wherein like reference characters designate corresponding parts in the several views. 
     Before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting. 
     As such, those skilled in the art will appreciate that the conception, upon which this disclosure is based, may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a circuit diagram of the present invention in open mode. 
         FIG. 2  is a circuit diagram of the present invention in continuous mode. 
         FIG. 3  is a circuit diagram of the present invention in security mode. 
         FIG. 4  is a cross sectional view of the thermally sensitive switch utilized in the invention in the open position. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With reference now to the drawings, and with note that as used in this specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the content clearly dictates otherwise, a preferred embodiment of the security switch is herein explained. As seen in  FIG. 1 , the switch, in its preferred embodiment, consists of three parallel circuits; all connected to a three-position manual control switch  12 , usually a Three Throw-Double Pole type, and power supply  10 . Continuous load circuit  26  is completed when switch  12  is in the continuously “on” position, shown in  FIG. 2 . In  FIG. 3 , the switch  12  is set on security mode, activating the indicator circuit  34 , with LED  16 , secondary heat circuit  30  and security circuit  28 . Secondary heat circuit  30  is a continuous circuit with small resistor  22  providing a constant heat source. Security circuit  28  contains a large resistor  20 , both acting as a primary heat source and having a smaller resistance than resistor  22 , and thermally sensitive switch  24 , which is normally closed. Resistance ratios are ideally that resistor  22  should have 10 to 15 times the resistance of resistor  20 . In the preferred embodiment, Resistor  20  has a resistance of 6,200 ohms and resistor  22  has a resistance of 75,000 ohms. Control circuit  32  connects security circuit  28  to load circuit  26  in series between the power supply  10  and switch  24 , ideally within enclosure  18  which contains both resistors  20 ,  22  and the switch  24 . 
     Referring to  FIG. 2 , the output load  14  would usually be a lamp, radio, or TV. With manual control switch  12  in the continuous position, the security circuit is bypassed so that power to the output load  14  is continuous. In  FIG. 3 , “Security” mode, input power is supplied to the output load  14  and to resistors  20  and  22 . Resistors  20  and  22  slowly heat thermally sensitive switch  24 , causing switch  24  to open, after a delay of over 15 minutes, turning off the output load  14  and resistor  20 . Secondary resistor  22  remains energized to slow the cooling of thermally sensitive switch  24 , which cools gradually until switch  24  closes again, repeating the periodic on-off cycles again and again until manual switch  12  is set to “Continuous” or “Off” by the user. Enclosure  18  isolates switch and resistors  20 ,  22  from the exterior environment, further ensuring that the cooling process is slowed down. Likewise, an external casing, enclosing the entirety of device components, further insulates the thermal switch  24  and resistors  20 ,  22 . 
     Optional thermal mass, or heat sink, including the material from which enclosure  18  is manufactured, added inside the enclosure of the timing module can be applied to slow both the heating cycle and the cooling cycle. The optional thermal mass can be the addition of any thermally conductive material, such as by inserting epoxy resin into the thermal module, or by the addition of a thick steel disc inserted inside the enclosure  18  on top of the thermally sensitive switch  24 . 
     The switch is activated by a bimetal disc  43  opening and closing the connection between the electrical contacts  48  in the switch  24 , shown in  FIG. 4 . Switch  24  comprises a movable arm  41 , held in place by retainer  46  and having additional contacts  48 , and a stationary arm  40 . The movable arm  41  operably connected to an actuating pin  45 , which is moved by the contortions of bimetal disc  43 . Bimetal disc  43  inherently has two metals with different expansion rates and thermal conductivity. Bimetal disc  43  is ideally made of brass and steel, though any combination of metals will suffice yielding different coefficients of thermal expansion and, therefore, varying thermal cycles. As such, one metal will expand more than the other, thus bending the disc  43  and moving the actuating pin  45  so that movable arm  41  connects and disconnects contacts  48 , opening and closing the circuit. In  FIG. 4 , Switch  24  is in the open position, as seen by the bulging bimetal disc  43  and slight open space (unnumbered) between movable arm  41  and contact  48 . In this embodiment of the switch  24 , the more expansive side of the bimetal disc  43  (ideally brass) is upward. However, the arrangement of the bimetal disc  43  in relation to the remainder of the switch  24  is dependant upon the arrangement of the remainder of the switch (i.e. the disc  43  may push the switch  24  open rather than pull it as shown) and will not remove the new configuration from the scope of the invention. Ideally, spacer  42  is provided to allow room for disc contortion and a sensing cap  44  closely covers the disc  43 , allowing for thermal interaction, and the rest of the switch assembly in case  49 . Also ideally, case  49  is riveted  51  to a terminal backing  50 . 
     Numerous additions may be made to the invention to increase utility. A timer override switch, common in the prior art, could be added as an override, preventing the switch  24  from actuating during inappropriate times. Likewise, a photoelectric resistor may be added for similar effect. Both of these devices are known in the prior art. 
     Although the present invention has been described with reference to preferred embodiments, numerous modifications and variations can be made and still the result will come within the scope of the invention. As an example, solid-state circuitry may be used to achieve the same effect as the resistors and other circuitry in this disclosure. No limitation with respect to the specific embodiments disclosed herein is intended or should be inferred.