Patent Publication Number: US-7218194-B2

Title: Tamperproof magnetic switch assembly

Description:
FIELD OF THE INVENTION 
   The present invention is directed toward magnetic switches that may be used as part of alarm systems to detect relative movement between a first and a second member such as a door and doorframe. More specifically, the present invention provides an improved magnetic switch assembly especially designed to defeat attempted unauthorized external manipulation. 
   BACKGROUND OF THE INVENTION 
   Security alarm systems often use magnetic switches attached to doors and windows for detecting unauthorized openings. One type of magnetic switch utilized is a reed switch. However, these switches are subject to unauthorized manipulation through use of, for example, an external magnet. Specifically, a compact high energy magnet may be positioned in proximity to the reed switch, which will then be operated (to either open or close depending on the control scheme). Once accomplished, an intruder can open the door or window without triggering the alarm system. 
   A number of magnetic switches have been proposed in the past to overcome the inherent limitation and serious deficiencies of reed switches including, U.S. Pat. Nos. 5,997,873; 5,530,428; 5,332,992; 5,673,021; 5,880,659; and 6,506,987. These switches typically include a pair of spaced apart switch elements with a shiftable body (e.g., a spherical ball) movable between a first position where the ball is in simultaneous contact with both switch elements and a second position out of simultaneous contact with the switch elements. An alarm circuit may be electrically coupled to the switch elements so as to detect movement of the body. However, these switches may still be manipulated by an externally applied magnetic force. 
   Other systems have been presented that also offer limited protection from external magnetic manipulation including, U.S. Pat. Nos. 6,506,987; 6,603,378; and 6,803,845. While the switch arrangements in these patents represent an improvement in the field, these switch arrangements suffer from some inherent problems. For example, while offering a degree of security against external magnetic fields in one plane, these switches may still be defeated by introducing an external magnetic force in one of several or in multiple planes. Another problem presented by these switches is that they are prone to misalignment, causing problems with accurate functioning of the system. In addition, these switches may be highly sensitive to the material to which they are mounted. For example, if these switches are mounted to a steel base, a portion of the magnetic field strength may be drawn away negatively affecting system performance. 
   What is desired then, is a system and method that will provide an improved magnetic switching device that is essentially undefeatable by application of an externally applied magnetic field. 
   It is further desired to provide a system and method that provides an improved magnetic switching device that may not be defeated with the application of an external magnetic field in one of several or multiple planes. 
   It is still further desired to provide a system and method that provides an improved magnetic switching device that reduces sensitivity to system misalignment. 
   It is yet further desired to provide a system and method that provides an improved magnetic switching device that is relatively insensitive to the material to which they are mounted. 
   SUMMARY OF THE INVENTION 
   These and other objects are achieved by the provision of an improved magnetic switching arrangement that detects relative movement between first and second members such as doors/door frames and are typically used to detect when one of the members is moved from a first position in close proximity with the second member, to a second position where the one member is moved to a remote position. The switch arrangement includes, a switch assembly, for mounting to the first member, the switch assembly having first and second switch elements in spaced relationship to each other, an electrically conductive body shiftable between a first position where the body is in simultaneous contact with both of the switch elements, and a second position where the body is not in contact with both of the switch elements. The switch assembly further includes a first magnetically attractive component adjacent the contacts in the first structural member and a second magnetically attractive component for mounting to the second member. The first and second attractive components are selected and located so that, when the first and second structural members are in the first, adjacent position, the body will be shifted to a position out of simultaneous contact with said first and second switch elements by virtue of a magnetic attraction between the body and the second attractive component. When the first and second members are in the second, remote position, the body will be shifted to a position into simultaneous contact with both of said switch elements by virtue of a magnetic attraction between the body and the first attractive component. 
   It is contemplated that the shiftable switch body may be permanently magnetized and the first and second attractive components may be complementary magnets or formed of steel or other magnetically susceptible material. Alternately, the first and second attractive components may be permanently magnetic whereas the shiftable body is formed of steel or other material, which is magnetically attractive to the components. 
   The improved magnetic switching arrangement further comprises in one advantageous embodiment, a magnetic flux director or concentrator. The director provides a lower reluctance path for an applied magnetic field thereby acting to “absorb” these fields from the surrounding space. These fields leave the director in regions of varying flux density around its space as a consequence of the material composition and design of the device. The fields emanate from the surfaces of the director with varying but relatively uniform energy levels. This field couples to the surrounding switches and/or bias rings within their narrow actuation angle creating localized balanced magnetic circuits. When the circuit is unbalanced due to the movement of the actuator or the introduction of an externally applied field the switches change state. 
   For example, the second attractive component may be provided as a relatively large permanent magnet that overcomes the attractive force of the relatively small first attractive component. Even though the flux director acts to reduce the magnetic flux applied to the shiftable switch body, there is still enough magnetic flux due to the relatively large size of the second attractive component that reaches the shiftable switch body, which overcomes the attractive force of the first attractive component. Therefore, in order to affect the shiftable switch body one would have to use a relatively large magnet that produces a magnetic field at least as strong as the second attractive component. This however, cannot be accomplished for a number of reasons. First, the relative spacing between the first and second members is relatively small, e.g. the door and doorframe will be provided with a relatively close fit. In this manner, a potential intruder is prevented from inserting the relatively large and bulky magnet required to shift the switch body due to the flux director, between the first and second members (e.g. between the door and doorframe). While a very low profile magnet and therefore a relatively weak magnet may be inserted, the switch is prevented from actuating. 
   A second reason it that if the potential intruder were to position the relatively large and powerful magnet on the surface of one of the members in order to actuate the switch body, a tamper switch will be actuated causing an alarm condition. Multiple tamper switches may be positioned to actuate upon the application of a magnetic field in virtually any plane in which the magnetic field component is located. Therefore, magnetic flux may only be applied in one plane from the outside of the device; however, the spacing is very small preventing a potential intruder from actuating the switch body. The presence of a large drive magnet makes it very difficult to permanently place a defeat magnet in the plane of operation. The high field strength of the drive magnet will likely attract the defeat magnet and dislodge it from the defeat actuation surface. 
   The provision of the flux director also minimizes the problem of misalignment associated with prior art devices. This is because the flux director has a tendency to gather in and channel any attractive force directed at the flux director. Additionally, the flux director helps to desensitize the switching device to the composition of the mounting surface due to the fact that magnetic flux is gathered and concentrated within a relatively narrow angle for actuation of the shiftable body. This means that, even if the overall magnetic field strength is affected due to the mounting material composition, such as for instance, steel, the system will still function properly because of the concentrated and directed magnetic field. 
   Also provided in the improved magnetic switching arrangement in another advantageous embodiment is a return flux director, which may be used to gather return magnetic flux and direct it back to the second attractive component. This further reduces and/or eliminates the problems associated with misalignment and further desensitizes the arrangement to the composition of the members. 
   Still further provided in another advantageous embodiment are various biasing rings that are positioned to encircle the shiftable switch body to provide for increased repeatability of the switching device. The biasing rings are provided to ensure that the switch body will actuate at substantially identical applied signal levels. It is also contemplated that multiple shiftable bodies (e.g. main and auxiliary switch contact arrangements) may effectively be utilized in connection with the flux director. The location of the biasing rings may further be varied depending upon the location of the multiple magnetic switches. Additionally, multiple attractive components may effectively be utilized to further increase system performance and repeatability. 
   Accordingly, in one advantageous embodiment, a magnetic switching device for detecting relative movement between a first and a second member is provided comprising, a switch assembly for mounting to the first member. In this embodiment the switch assembly includes, a first switch element and a second switch element, the second switch element positioned apart from the first switch element, an electrically conductive shiftable body, a first attractive component, and a flux director positioned in proximity to the shiftable body. The shiftable body is provided such that it is movable between a first position where the shiftable body is in simultaneous contact with the first and second switch elements, and a second position where the shiftable body is out of simultaneous contact with the first and second switch elements. The magnetic switching device further comprises a second attractive component for mounting to the second member. The director provides a lower reluctance path for an applied magnetic field thereby acting to “absorb” these fields from the surrounding space. The magnetic fields emanating from the director couples to the surrounding switches and/or bias rings, which when used comprise the first attractive component within their narrow actuation angle. In addition, the first and second attractive components are positioned such that when the first and second members are in proximity to each other in a proximal position, the magnetic flux directing device allows a threshold level of magnetic flux to be applied to the shiftable body so that the shiftable body is moved to one of the first or second positions, and when the first and second members are moved out of proximity to each other in a distal position, the shiftable body is moved to the other of the first or second positions. 
   In another advantageous embodiment a magnetic switching device for detecting relative movement between a first and a second member is provided comprising, a switch assembly that has an electrically conductive shiftable body that shifts between simultaneous contact with two switch elements and non-simultaneous contact with the two switch elements based upon applied magnetic fields generated by first and second attractive components. In this advantageous embodiment the switch assembly further includes a flux director positioned in proximity with the shiftable body. The director provides a lower reluctance path for an applied magnetic field thereby acting to “absorb” these fields from the surrounding space. The magnetic fields emanating from the director couples to the surrounding switches and/or bias rings, which when used comprise the first attractive component within their narrow actuation angle. In addition, the first and second attractive components are positioned such that when the first and second members are in proximity to each other in a proximal position, the magnetic flux directing device allows a threshold level of magnetic flux to be applied to the shiftable body so that the shiftable body is moved to one of the first or second positions, and when the first and second members are moved out of proximity to each other in a distal position, the shiftable body is moved to the other of the first or second positions. 
   In still another advantageous embodiment, a magnetic switching device for detecting relative movement between a first and a second member and for sending a signal indicative of the relative movement to a control panel is provided comprising, a switch assembly that has an electrically conductive shiftable body that shifts between simultaneous contact with two switch elements and non-simultaneous contact with the two switch elements based upon applied magnetic fields generated by first and second attractive components. The switch assembly further including, the first and second attractive components being positioned such that when the first and second members are in proximity to each other in a proximal position, the magnetic flux directing device allows a threshold level of magnetic flux to be applied to the shiftable body so that the shiftable body is moved to one of the first or second positions, and when the first and second members are moved out of proximity to each other in a distal position, the shiftable body is moved to the other of the first or second positions. The magnetic switching device further comprises, a resistor network positioned in the magnetic switching device for sending, via a set of control leads, a signal indicative of the relative movement between a first and a second member to the control panel. 
   Other objects of the invention and its particular features and advantages will become more apparent from consideration of the following drawings and accompanying detailed description. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  illustrates a magnetic switch depicted in use for protecting a door; 
       FIG. 2  depicts the construction and operation of the magnetic switch when the door is closed according to  FIG. 1 ; 
       FIG. 3  is a sectional view similar to  FIG. 2 , but illustrating the operation of the magnetic switch when the door is open; 
       FIG. 4  is a block diagram of one advantageous embodiment of the present invention utilizing the magnetic switch according to  FIG. 1 ; 
       FIG. 4A  is a side view showing the flux director according to  FIG. 4 . 
       FIG. 4B  is an edge view showing the flux director according to  FIG. 4 . 
       FIG. 4C  is a end view showing the bias ring(s) according to  FIG. 4 . 
       FIG. 4D  is an edge view showing the bias ring(s) according to  FIG. 4 . 
       FIG. 5  is a block diagram of another advantageous embodiment of the present invention according to  FIG. 4 ; 
       FIG. 5A  is a block diagram illustrating another advantageous embodiment of the present invention according to  FIG. 5 ; 
       FIG. 5B  is a block diagram illustrating yet another advantageous embodiment of the present invention according to  FIG. 5 ; 
       FIG. 5C  is a block diagram illustrating yet another advantageous embodiment of the present invention according to  FIGS. 4 and 5 . 
       FIG. 6  is a block diagram of another advantageous embodiment of the present invention according to  FIG. 4 ; 
       FIG. 6A  is a block diagram of still another advantageous embodiment of the present invention according to  FIG. 6 ; and 
       FIG. 7  is a schematic illustrating the positioning of a resistor network in the switch assembly. 
   

   DETAILED DESCRIPTION OF THE DRAWINGS 
   Turning now to the drawings,  FIG. 1  illustrates a magnetic switch  10  (dashed lines) shown used with a doorframe  12  and door  14 . Electrical leads  16 ,  18  are operatively coupled with the switch  10 . While FIG.  2  illustrates a contact that is normally open when the door is in the secure position, it is contemplated that a normally closed contact when the door is in the secure position is equally applicable. 
   The switch  10  includes a switch assembly  20  secured to frame  12 , as well as a second attractive component  22 , which is mounted to door  14 . The switch assembly  20  may include a housing  24  having a circumscribing annular sidewall  26 , an integral concavo-convex bottom wall  28  and a top cover  30 . Preferably, the integral sidewall and bottom wall  26 ,  28  presents a circumscribing flange  32  and is formed of a suitable non-magnetic, electrically conductive material, such as for instance, cupro-nickel alloy. The top cover  30  includes an outboard flange  34  adapted to mate with flange  32 , and a central glass or ceramic nonconductive plug  38 . The flange  34  may also be formed of a suitable non-magnetic, electrically conductive material. 
   The assembly  20  also includes an elongated substantially upright first switch element  40  which as shown extends downwardly through plug  38  to a point spaced above bottom wall  28 , the latter having an annular contact surface  42  which serves as the second switch element. 
   A shiftable body  44  is located within housing  24  and is formed of electrically conductive material. Preferred configurations of body  44  include substantially spherical balls as well as cylinders. 
   The overall assembly  20  further includes a first attractive component  45  associated with housing  24 . In the illustrated embodiment, the component  45  is situated slightly below housing  24  and is laterally offset relative to the central axis of the housing. 
   The top cover  30  is welded to sidewall  26  at the facing contact between the flanges  32  and  34 , thereby creating a hermetically sealed internal chamber  46 . It is preferred that the chamber  46  be filled with an inert gas such as for example, argon. 
   As illustrated, the housing  24  and first attractive component  45  may be located within a mounting box  48  positioned within an appropriately sized recess in frame  12 . However, such a mounting arrangement is not essential. 
   The second attractive component  22  is mounted to door  14 , for example, near the top of the door. When the door  14  is closed relative to frame  12 , it will be seen that the component  22  is directly in juxtaposition to housing  24 . When the door  14  is opened, the component  22  is shifted away from the housing  24 . 
   The materials used in fabricating the first and second attractive components  45 ,  22  and body  44  can be varied, so long as the operational principles of the switch  10  are maintained. For example, and in preferred forms, the body  44  may be formed of a permanently magnetized material. Suitable materials include an appropriate samarium-cobalt alloy with a thin (usually about 0.001–0.002″) outer coating of nickel for wear purposes or neodynium iron boron. In such an instance, the attractive components  45  and  22  may be formed of steel (e.g., partially annealed steel) or of complementary magnetized material relative to the body  44 . Alternately, the first and second components  45 ,  22  may be formed of permanently magnetized material while the body  44  is formed of any material, which is magnetically attracted to the first and second components. As explained in more detail hereafter, the goal in selecting the materials for the components  45  and  22  and body  44  is to assure that the body  44  may be appropriately magnetically shifted when the door  14  is moved between the closed and open positions thereof. 
   Specifically, and referring to  FIG. 2 , it will be seen that, when the door  14  is closed relative to frame  12 , the body  44  is shifted laterally by virtue of a magnetic attraction between the second attractive component  22  and the body  44 , so as to hold the body  44  in the  FIG. 2  position out of simultaneous contact with the switch elements  40 ,  42 . Of course, in this orientation, the magnetic attraction between component  22  and body  44  is greater than and overcomes the magnetic attraction between body  44  and first attractive component  45 . The offset position of the component  45  augments this differential attraction relative to body  44 . 
   When the door  14  is open so that second attractive component  22  is remote from the switch assembly  20 , the body  44  is magnetically shifted to the  FIG. 3  position thereof, i.e., in simultaneous contact with the switch elements  40 ,  42 . As will be readily understood, this shifting is effected because of the magnetic attraction between the body  44  and first attractive component  45 . 
   The relative magnetic strengths or susceptibilities of the first and second components  45 ,  22  relative to body  44  must be considered in the design of switch  10 . That is, the magnetic attraction generated between the body  44  and component  22  when the door  14  is closed must be significantly stronger than the countervailing magnetic attraction between the body  44  and the first component  45 . 
   Turning now to  FIG. 4 , an advantageous embodiment of the improved magnetic switching arrangement is illustrated. This configuration includes switch  10  and further includes flux director  60 . 
   Flux director  60  provides a lower reluctance path for an applied magnetic field thereby acting to “absorb” the field from second attractive component  22 . The field leaves the director in regions of varying flux density around its space as a consequence of the material composition and design of the device. The field couples to, for example, body  44  (which may comprise a door contact or switch) within its relatively narrow actuation angle creating a localized balanced magnetic circuit. However, when the circuit is unbalanced due to movement of the actuator or the introduction of an externally applied field, body  44  changes state due to interaction with magnet  45  that comprises a first attractive component in this embodiment, creating an alarm condition. The presence of a large drive magnet makes it very difficult to permanently place a defeat magnet in the plane of operation. The high field strength of the drive magnet will likely attract the defeat magnet and dislodge it from the defeat actuation surface. It is contemplated that additional door contacts or switches may be provided as desired. 
   Also illustrated in  FIG. 4  is the internal resistor network  82 , which will be discussed in greater detail in connection with  FIG. 7 . While the internal resistor network  82  is shown located with the components mounted to the first member  12 , it is contemplated that the internal resistor network  82  may further be located with the components mounted to second member  14 . 
     FIGS. 4A and 4B  illustrate one advantageous embodiment of flux director  60  including preferable dimension ranges in inches.  FIG. 4A  illustrates a side view of flux director  60 , while  FIG. 4B  shows a range of thickness measurements for flux director  60 . It is contemplated that flux director  60  typically will comprise a ferrous material, but may comprise any magnetically permeable material including for example but not limited to, nickel. 
   Also shown in  FIG. 4  is auxiliary switch  66 , which is similar in operation to main switch  64 . It should be noted that these switches (main switch  64 , auxiliary switch  66 , etc.) may be selected having any desired logic, whether normally open or normally closed and is should not be viewed as a limitation of the present invention. In one embodiment, auxiliary switch  66 , includes body  44 ′ and magnet  45 ′, which comprises a first attractive component and may be used to switch a variety of system components as desired. Alternatively, both main switch  64  and auxiliary switch  66  may be provided with biasing rings  68 ,  68 ′, which are positioned to surround body  44 ,  44 ′ and comprise the first attractive components. One or more bias rings  68 ,  68 ′ may be positioned around body  44 ,  44 ′ as desired. Bias rings  68 ,  68 ′ are provided to increase switching repeatability such that for an applied signal level or magnetic field strength, body  44 ,  44 ′ will always actuate. 
     FIGS. 4C and 4C  illustrate one advantageous embodiment for bias rings  68 ,  68 ′ including preferable dimension ranges in inches.  FIG. 4C  depicts and view looking down the end of the bias ring with a preferable inside diameter (ID) provided.  FIG. 4D  is a side view of the bias ring providing both a preferable outside diameter (OD) measurement, and a measurement of the thickness (T) of the ring. The thickness (T) of the bias rings typically will range from about 0.01 inches to about 0.2 inches. It is contemplated that bias rings  68 ,  68 ′ typically will comprise a highly permeable material, such as for example but not limited to, iron, nickel and/or combinations thereof. 
   Also provided is tamper switch  70 ,  70 ′. One or more tamper switches may be provided to indicate the application of an applied external magnetic field. If a potential intruder were to apply an external magnetic field to assembly  20  in a plane other than from the direction of the second attractive component  22 , the applied external magnetic field would cause tamper switch(es)  70 ,  70 ′ to actuate causing an alarm condition. 
   Also provided in  FIG. 4  is pry tamper switch  72 , which will indicate whether assembly  20  has been moved relative to first member  12 , also, providing an alarm upon activation. 
     FIG. 5  is an illustration of yet another advantageous embodiment of the present invention similar to that described in connection with  FIG. 4  but further including return flux director  62 . Return flux director  62  is constructed and operates similar to flux director  60  in that applied magnetic flux is gathered and channeled as desired. In this case, magnetic flux is directed back to second attractive component  22 . Return flux director  62  has a tendency to increase the magnetic field strength between switch assembly  20  and second attractive component  22 . This increased field strength further desensitizes the assembly  20  to the composition of first member  12  and second member  14 . In addition, misalignment problems are further reduced, and the operational gap is increased. 
     FIG. 5A  is an alternative embodiment according to  FIG. 5  in which another second attractive component  22 ′ is positioned adjacent to the return flux director  62 . Providing another second attractive component  22 ′ opposite in polarity to second attractive component  22  allows the magnetic circuit to close more tightly, increasing the flow of magnetic flux through the circuit. This in turn allows the distance between the members to be increased while maintaining a high level of circuit performance. 
     FIG. 5B  illustrates still another advantageous embodiment of the present invention, which is similar to that show in  FIG. 5A , but further includes shim(s)  80  that may be used with and/or position adjacent to second attractive component  22 ′. The shim material of shim may comprise in one advantageous embodiment, a material having relatively good permeability and high saturation characteristics, including for example the material of the bias rings. While the shim(s)  80  is shown as only adjacent to second attractive component  22 ′, it is contemplated that shim(s)  80  could extend across both second attractive component  22  and  22 ′. 
   While shim(s)  80  and second attractive component  22 ′ are shown with the component located on the second member  14 , it is contemplated that they may further be located with the parts located on first member  12  or in both locations as illustrated in  FIG. 5C  with shim  80  positioned on first member  12  adjacent to shiftable body  44 . 
   It is still further contemplated that the switch and/or magnet assembly  20  may be provided with a metal back plate(s)  74  for compensation purposes. Also, high permeability shims may be used in connection with second attractive component  22 . The shim material of shim may comprise in one advantageous embodiment, that of bias rings or other high permeability material. 
     FIG. 6  is yet another illustration of an advantageous embodiment of the present invention including flux director  60  and two second attractive components  22 ,  22 ′ positioned in second member  14 . This embodiment again provides an increased magnetic field strength between the first and second members. It is also contemplated that the two second attractive components  22 ,  22 ′ may be installed having opposite polarity at each end of switch assembly  20 . It is also contemplated that many of these embodiments may be effectively used together in various combinations to increase overall system performance and repeatability as desired for a given application. 
     FIG. 6A  is still another advantageous embodiment of the present invention including two second attractive components  22 ,  22 ′ and return flux director  62  provided in the shape of a rectangular bar located below the two second attractive components  22 ,  22 ′. Again the two second attractive components  22 ,  22 ′ are provided as opposite polarity magnets and the optional return flux director  62  further increases flow of magnetic flux in the circuit increasing system performance and allowing the distance between the members to be increased if necessary. 
     FIG. 7  is an illustration of one particularly advantageous embodiment which includes the internal resistor network  82  according to the various embodiments previously described herein. Typically it has been standard practice in industry to terminate the electrical leads ( 86 ,  88 ) that are connected to a door switch  64  with resistors (R 1 ) and (R 2 ) at a monitoring panel  84  for the alarm system. When for example, the unit is in the secure position the door switch  64  is closed and the resistance at the monitoring panel  84  may equal (R 1 ). When however, the unit is not secure the door contact is open and the total resistance at the monitoring panel  84  will then be equal to (R 1 )+(R 2 ). Without resistor the indicated resistance is either 0Ω (secure) or infinite Ω (not secure). Again, it is contemplated that many differing switching logic configurations may be used. This configuration is merely provided as an example of one such configuration and is not meant to be a limitation on the invention. 
   A problem with this arrangement is here identified. If an intruder shorts the electrical leads ( 86 ,  88 ) somewhere along the path from the switch to the monitoring panel  84  the total resistance would always read 0Ω. The monitoring panel  84  then would interpret this as the unit is constantly secure allowing an intruder to bypass the security. However, positioning the resistors (R 1 ) and (R 2 ) inside of the door switch unit eliminates the intruder&#39;s ability to bypass the system. This is because if the potential intruder where to short electrical leads ( 88 ,  92 ), rather than reading resistance (R 1 ) or “secure”, the system will read 0Ω or fault, which can activate an alarm condition. 
   Other benefits of this arrangements is that it eliminates the additional labor costs associated with installing the resistors (R 1 ) and (R 2 ) in the control panel  84  as these are already factory installed in the device itself, and eliminates any potential error the installer may make in connecting the resistors (R 1 ) and (R 2 ) to the system. 
   It should further be noted that, even though the internal resistor network  82  is shown ( FIG. 4 ) located with the components mounted to the first member  12 , it may also be positioned adjacent to the components mounted to second member  14 . 
   Although the invention has been described with reference to a particular arrangement of parts, features and the like, these are not intended to exhaust all possible arrangements or features, and indeed many other modifications and variations will be ascertainable to those of skill in the art.