Abstract:
A method and apparatus for protecting a low voltage system, such as an alarm system, is described. The method and apparatus includes power line surge protector and a plurality of low-voltage surge protectors housed within a common cabinet. The low-voltage surge protectors are mounted in connectors that provide physical support as well as electrical connections. These electrical connections are routed to a set of input and output terminals by a printed circuit board that also provides support for the connectors and terminals. The combination of power line surge protectors and low-voltage surge protectors may help reduce damage to equipment such as an alarm system during power surges, perhaps caused by electrical storms or heavy electrical equipment being operated nearby. Because of the radio frequency noise emanating from the power line and the power line surge protector, a shield is provided that reduces the amount of noise that is transferred to the low-voltage signal paths.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     This invention relates to a method and apparatus for shielding low voltage equipment.  
         [0003]     2. Description of the Prior Art  
         [0004]     Security systems often comprise a network of initiating circuits such as smoke detectors, glass break detectors and intrusion detection switches. Often, they also comprise a network of notifying circuits such as strobe lights, horns and the like. Most often, these devices are connected to the alarm system by a dedicated wiring system using low voltages to signal between units. Furthermore, the alarm system is often connected to a phone line or network connection to communicate status and alarms to remote locations. And, of course, the alarm system needs power to operate, usually home or business AC line voltage, perhaps 120V or 220V. All of these wired connections act as antenna and conduit to power surges that might occur due to many reasons such as electrical storms or turning on/off heavy equipment and the like. These power surges introduce the risk of damage to the alarm system, whereby; a surge on one of the elements may destroy the entire alarm system.  
         [0005]     In the past, several discrete products were deployed to protect the alarm system. One system may have been deployed to protect the initiating circuits; another for the notifying circuits; and another for the power. Additionally, if network connections or phone connections are made to the alarm system, discrete network surge protectors and phone line protectors may be deployed.  
         [0006]     What is needed is an integrated system to protect the alarm system from external power surges, electrostatic discharge, lightning and other hazardous forces.  
       SUMMARY OF THE INVENTION  
       [0007]     For the purposes of this application, the term alarm system will refer to any alarm system, perhaps contained within a premise, and connected to low-voltage initiating circuits and/or low-voltage notifying circuits and/or a phone line.  
         [0008]     In one embodiment, an apparatus for protecting a low-voltage network is described including a metal chassis. Within the metal chassis is a surge protector that has power input terminals, power output terminals and a surge protection circuit. The surge protection circuit passes power from the power input terminals to the power output terminals while reducing the transmission of potential power surges emanating from the power input terminals to the power output terminals. Also housed within the metal chassis is a low-voltage connection circuit board that has a shield, a plurality of low-voltage input terminals, a plurality of low-voltage output terminals and a low-voltage surge protector connector. The low-voltage connection circuit has printed circuit paths that are configured to connect the plurality of low-voltage input terminals and the plurality of low-voltage output terminals to the low-voltage surge protector connector. Additionally, there is a plurality of plug-in low-voltage surge protectors also housed within the chassis, each having a connector that mates with the low-voltage surge protector connector.  
         [0009]     In another embodiment, a means for protecting a low-voltage network is disclosed, including a means for enclosing and a means for providing a low-voltage connection circuit board that has a plurality of low-voltage input connectors, a plurality of low-voltage output connector and a plurality of low-voltage protection module connectors. Also, there is a means for protecting a plurality of low-voltage signals from power surges that includes a plurality of low-voltage surge protectors each having a connector for mating with one of the plurality of low-voltage protection module connectors. Also included is a means for shielding the plurality of low-voltage signals from radio frequency noise, comprising a printed circuit layer substantially covering most of the bottom of said low-voltage connection circuit board.  
         [0010]     In another embodiment, a method of protecting a low voltage network is disclosed. The method includes providing a power line surge protector having a power line input, a power line output and a power line surge protection circuit, providing a plurality of low voltage surge protectors each having a male low-voltage surge protector connector and mounting the plurality of low voltage surge protectors on a low-voltage connection circuit board that has a plurality of low-voltage input terminals, a plurality of low-voltage output terminals and a plurality of female low-voltage surge protector connectors for mating with the male low-voltage surge protector connector. Also included is shielding the low-voltage connection circuit board from said power line surge protector and enclosing the plurality of low-voltage surge protectors, the low-voltage connection circuit board and said power line surge protector within a metal chassis. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     The invention can be best understood by those having ordinary skill in the art by reference to the following detailed description when considered in conjunction with the accompanying drawings in which:  
         [0012]      FIG. 1  illustrates a front view of an embodiment of the present invention.  
         [0013]      FIG. 2  illustrates internal components of an embodiment of the present invention.  
         [0014]      FIG. 3  illustrates a view of an embodiment of a surge protector of the present invention with the top cover removed.  
         [0015]      FIG. 4  illustrates a front view of an embodiment of the present invention.  
         [0016]      FIG. 5  illustrates a view of the bottom view of a low-voltage circuit board according to an embodiment of the present invention.  
         [0017]      FIG. 6  illustrates a schematic view of an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]     Reference will now be made in detail to the presently preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings.  
         [0019]     Throughout the following detailed description, the same reference numerals refer to the same elements in all figures.  
         [0020]     Referring to  FIG. 1 , a front view of the present invention, the system is enclosed in a metal chassis  105 , preferably metal such as aluminum, copper or steel, with a hinged cover  110 . The chassis may be painted or not, or may be enclosed by an outer shell made of, perhaps, an insulative material such as plastic without veering from the present invention. Furthermore, the inside of the metal chassis may be insulated to prevent loose wires from shorting to the metal chassis. This insulation may be, for example, plastic or an insulating paper such as Fiberfax® or NOMEX®. Shown is a power line surge protector  120  with power input terminals  125 , power output terminals  130  and dry contact terminals  135 . The surge protector may be a typical surge protector used to protect electrical equipment that is connected to its power output terminal from power line surges received on its power input terminals. The set of dry contact terminals  135  may be used to convey the status of the surge protector to a remote location.  
         [0021]     Continuing with  FIG. 1 , two low-voltage protection modules ( 140  and  150 ) are shown. These low-voltage protection modules ( 140  and  150 ) plug into a low-voltage connection circuit board  155 . In general, for this application, consider low-voltage to represent any voltage lower than the line voltage input, in many cases, lower than 120V AC. For example, many alarm companies use different voltages that are lower than 120V to detect and control. The low-voltage connection circuit board  155  has connectors (not shown) for connecting to and supporting the low-voltage protection modules ( 140  and  150 ), low-voltage input terminals  160 , low voltage output terminals  165  and printed circuit paths connecting the low-voltage input terminals  160  to the connectors for the low-voltage protection modules ( 140  and  150 ) and connecting the low-voltage output terminals  165  to the connectors for the low-voltage protection module. In general, the low-voltage protection modules  140 / 150  protect circuits such as alarm circuits that operate at low-voltages such as voltages of 12V or less. Shown in  FIG. 5  is a shield  590  that is a printed circuit board layer of the low-voltage connector circuit board. This shield runs substantially across the entire bottom surface of the low-voltage connector circuit board  155  and helps prevent interference such as radio frequency noise that emanates from the power line surge protector  120  from reaching the low-voltage circuits. In another embodiment, the shield may be an insulated metallic material such as copper or aluminum foil attached to the bottom of the low-voltage connector circuit board. Furthermore, a sheet of plastic or a fire resistant insulating paper such as Fiberfax® or NOMEX® may be placed between the power line surge protector  120  and the low-voltage protection connection circuit board  155  to reduce the possibility of a loose power line wire coming into contact with a low-voltage circuit.  
         [0022]     Referring to  FIG. 2 , a view of the internal components of an embodiment of the present invention is shown without the metal chassis. Shown is the power line surge protector  120  with power input terminals  125 , power output terminals  130  and dry contacts  135 .  
         [0023]     Also shown in  FIG. 2 , is a low-voltage connection circuit board  155  with low-voltage input terminals  160 , low-voltage output terminals  165  and female connectors  210  for making electrical contact with a mating male connector  220  on the low-voltage protection modules ( 140  and  150 ). The low-voltage protection modules may be physically held in place by the female connectors  210  or in other embodiments may be supported by other means such as a retainer clip or the like. There are no electrical connections between the low-voltage connection circuit board  155  and the power line surge protector  120 , but because both are mounted within the same metal chassis  105 , there is a potential for radio frequency energy to pass from the power line surge protector  120  through the air or through the metal chassis  105  and into the low-voltage connection circuit board  155 , possibly interfering with the low-voltage signaling that is being protected. To reduce this potential, the low-voltage circuit board  155 , provides a shield  590  running substantially the full surface area of the low-voltage connection circuit board  155 . The shield  590  may be a layer of the low-voltage connection circuit board  155  or, in some embodiments, may be a discrete metal shield that is attached to the bottom of low-voltage circuit board  155 , perhaps copper or aluminum foil, preferably insulated so as to not create a short between other components mounted on low-voltage circuit board  155 .  
         [0024]     Referring to  FIG. 3 , an exploded view of an embodiment of a power line surge protector  120  of the present invention with the top cover removed is shown with cover removed. In this embodiment, the power line surge protector components are mounted to a power line surge protector circuit board  310 , with surge protector inputs  325 , surge protector outputs  330  and dry contacts  335 . When the cover is installed, the power line surge protector inputs  325  connect to power input terminals  125 , the power line surge protector outputs  330  connect to power output terminals  130  and dry contacts  335  connect to dry contact terminals  135 .  
         [0025]     Referring to  FIG. 4 , a front view of an embodiment of the present invention is shown. The system is enclosed in a metal chassis  105 , preferably metal such as aluminum, copper or steel, with a hinged cover  110 . The chassis may be painted or not, or may be enclosed by an outer shell made of, perhaps, an insulative material such as plastic without veering from the present invention. Shown is a power line surge protector  120  with power input terminals  125 , power output terminals  130  and dry contact terminals  135 . The power line surge protector may be a typical surge protector used to protect some electrical equipment that is connected to its power output terminal from power line surges received on its power input terminals. Also shown is a set of dry contact terminals  135  that may be used to convey the status of the surge protector to a remote location.  
         [0026]     Continuing with  FIG. 4 , six low-voltage protection modules ( 410 ,  420 ,  430 ,  440 ,  450  and  460 ) are shown. These low-voltage protection modules plug into a low-voltage connection circuit board  470 . The low-voltage connection circuit board  470  has connectors (not shown) that accept the low-voltage protection modules, low-voltage input terminals  475 , low voltage output terminals  480  and printed circuit paths connecting the low-voltage input terminals  475  to the connectors for the low-voltage protection modules ( 410 ,  420 ,  430 ,  440 ,  450  and  460 ) and connecting the low-voltage output terminals  470  to the connectors for the low-voltage protection module. Not shown is a shield that is a printed circuit board layer of the low-voltage connector circuit board. This shield runs substantially across the entire bottom surface of the low-voltage connector circuit board and helps prevent interference, such as radio frequency noise emanating from the power line surge protector, from reaching the low-voltage circuits. In another embodiment, the shield may be an insulated metallic material such as copper or aluminum foil attached to the bottom of the low-voltage connector circuit board.  
         [0027]      FIG. 5  shows a view of the bottom of the low-voltage connection circuit board  155 , according to an embodiment of the present invention. In this, the bottom layer of the low-voltage connection circuit board  155  has pins  560  for holding the low-voltage input connector ( 160 ) terminals, pins  565  for holding the low-voltage output connector ( 165 ) terminals and pins  510  for holding the connectors ( 210  not shown) that mates with the low-voltage protection modules ( 140  and  150 ). Shown is a ground plane  590  that is connected to the signal ground pins of the low-voltage input connector  160  and connected to the signal ground pins of the low-voltage output connector  165 . The ground plane  590  covers a substantial portion of the bottom surface of the low-voltage circuit board  155 . This ground plane forms a shield that helps prevent radio frequency radiation from passing from the metal chassis  105  into the low-voltage circuits that are being protected. Also visible are two of the low voltage protection modules  140  and  150  that are installed in the connector  210  (not shown) that mates with the low voltage protection modules.  
         [0028]      FIG. 6  shows a schematic diagram  600  of the present invention. Power input comes from a power source, perhaps building wiring passing  120 V or  220 V AC power and enters the system on, perhaps, three wires  690 , perhaps a hot, neutral and ground path. The power wires  690  are connected to terminals on the power line surge protector  625 . The power line surge protector  625  helps prevent power surges present at the building power source, from passing through to the alarm system  675 , which is connected to the surge protector  625  by, perhaps, three wires  695 , again, perhaps a hot, neutral and ground path.  
         [0029]     The alarm system  675  has low-voltage inputs that are connected to a low-voltage surge protector  630  that are, in turn, connected to various detection elements; in this case a smoke detector  640  and a glass break detector  650 . The alarm system  675  has low-voltage outputs also connected to another low-voltage surge protector  620 , in turn, connected to a signaling element, in this case a horn  660 . The low-voltage surge protectors help prevent power surges that emanate from the detectors and notifying devices from passing through to the alarm system, thereby helping prevent failure of the entire alarm system due to power surges, perhaps those caused by electrical storms and the like. This example shows only a few of the possible initiating circuits (smoke detector  640  and glass break detector  650 ) and notifying circuits (horn  660 ) that may be connected to the alarm system  675 . Many other types of protection circuits may be used, including, for example, a phone line surge protector, a two pair hybrid line protector, an initiating circuit protection module and a notifying circuit protection module. Additionally, often the alarm system  675  may communicate with dispatch stations or other alarm systems through phone lines or network lines that are also susceptible to power surges. The phone line connection  680  from the alarm system  675  is connected to a low-voltage phone line protection circuit  610  that is, in turn connected to a phone line  670 . In this example, three low-voltage surge protectors are shown, but any number may be enclosed in the same metal chassis  105 . Additionally, the low-voltage surge protector  630  is shown having two independent surge protector circuits, one for the smoke detector  640  and another for the glass break detector  650 . In other embodiments any number of independent low-voltage surge protector circuits and connectors may be provided in each low-voltage surge protector.  
         [0030]     Equivalent elements can be substituted for the ones set forth above such that they perform in substantially same manner in the same way for achieving the same result.  
         [0031]     It is believed that the system and method of the present invention and many of its attendant advantages will be understood by the foregoing description. It is also believed that it will be apparent that various changes may be made in the form, construction and arrangement of the components thereof without departing from the scope and spirit of the invention or without sacrificing all of its material advantages. It is the intention of the following claims to encompass and include such changes.