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.
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.
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 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 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.
Turning now to the drawings,
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 in 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
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
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
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, 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
Also shown in
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
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.
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.
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 (R1) and (R2) inside of the door switch unit eliminates the intruder's ability to bypass the system. This is because if the potential intruder where to short electrical leads (88, 92), rather than reading resistance (R1) 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 (R1) and (R2) 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 (R1) and (R2) to the system.
It should further be noted that, even though the internal resistor network 82 is shown (
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.