Magnetically retained connecting cable incorporating magnetically operated switch

A connecting and sensing device and a method for its use in a system for electrically monitoring physical security, including a magnetically operated switch, such as an encapsulated magnetic reed switch, and a quantity of ferromagnetic material located in a fixed position relative to the magnetically operated switch. The switch is connected electrically to an alarm system control circuit and is physically restrained by a flexible cable or the like. An actuating magnet may be attached either to an object whose unauthorized removal is to be detected, or to a fixed object. The actuating magnet is held within a holder including a cavity which permits the magnetically actuated switch and ferromagnetic material to be placed in a predetermined location wherein a magnetic field of a desired polarity and strength produces a desired condition in the magnetically operated switch. The switch is retained in the desired location relative to the actuating magnet by the magnetic attraction between the actuating magnet and the ferromagnetic material. Unauthorized removal of the object being monitored by the use of the sensor results in the ferromagnetic material and the magnetically operated switch being pulled away from the actuating magnet, causing the switch to produce an electrically detectable change of state.

BACKGROUND OF THE INVENTION 
The present invention relates to improvements in sensors for use in 
physical security alarm system circuits, and particularly to a 
magnetically retainable connector cable incorporating a magnetically 
operated switch for incorporation in an alarm system for detection of 
unauthorized removal of an object from its proper location. 
It has long been known to use magnetically operated proximity switches in 
security systems to detect unauthorized opening of doors, windows, gates, 
and the like. Typically, a magnetically operated switch such as a magnetic 
reed switch is fixedly mounted on a stationary structure and a permanent 
magnet is appropriately mounted on the movable window, door, or gate. When 
the movable object is in a predetermined position, the magnet actuates the 
switch, appropriately opening or closing an electrical circuit connected 
to an alarm system control device designed to respond appropriate. The 
usefulness of such previously known magnetically operated switch 
assemblies has depended upon the ability to mount an actuating magnet in a 
position where it will reliably actuate a magnetically operated switch 
whenever the door, gate, etc., is in an appropriate position. Such a 
system depends, however, on the door, etc., returning predictably to a 
position which must usually be within about an inch of a reference 
location. 
In many instances, it is desirable to have an electrical indication 
available to an alarm system control device whenever a valuable movable 
object is removed from its authorized location. For example, freight 
containers, trailer trucks, construction equipment, boats, and the like 
are frequently left unattended in open lots or alongside unattended piers 
where there is no need for them to be precisely located. It would be 
possible to provide connector cables incorporating special plugs, with 
corresponding jacks or sockets being provided on the movable articles to 
be protected, to complete an electrical circuit to an alarm system. Such 
plugs and sockets would be susceptible to short-circuits or corrosion of 
their contact points caused by exposure to the weather, however, and they 
would therefore present a serious problem of poor reliability. 
Encapsulated magnetic reed switches have been used in intrusion alarm 
system sensor circuits in order to avoid exposure of switch contacts or 
electrical connector contacts to the weather, but as previously explained, 
the previous use of such magnetically operated switch assemblies has 
required an actuating magnet carried on a movable object to be relatively 
precisely located with respect to the magnetically operated switch. 
Previously known magnetically operated switch devices are therefore not 
readily useable to protect objects which are floating on water. Nor are 
all such devices well adapted for use on overhead doors, whose tracks 
often permit up to an inch or more of movement, on fence gates which often 
move in the wind, or to protect heavy equipment which must be left on a 
construction site between work shifts, in unpredictable positions. 
In addition to being reliable, despite imprecise location or movability of 
the protected object, and despite exposure to the weather, a theft 
detection device needs to be easily operable and to be resistant to 
damage. Furthermore, such a device, if it includes a magnetically operated 
switch, needs to be resistant to deception, as by the use of hand-held 
magnets or by unauthorized removal of the actuating magnet, along with the 
switch assembly, from the object whose theft is to be detected by the 
device. 
What is needed, therefore, is an improved electrical cable and connecting 
device for use in conjunction with a security alarm control system which 
is capable of reliable operation to detect removal of a portable or mobile 
object from its proper location without being susceptible to weather, and 
which does not require the object protected to be precisely located or 
completely stationary. 
SUMMARY OF THE INVENTION 
The present invention provides an improved connecting and sensing device 
for detecting unauthorized movement or theft of objects, especially 
portable and mobile objects, from their authorized locations. The device 
of the present invention includes a magnetically operated electrical 
switch device connectable to a theft detection alarm system circuit by 
flexible electrical conductors, preferably contained in an armored cable, 
and an actuating magnet which completes a physical connection between the 
object to be protected and an alarm control system, while magnetically 
actuating the switch device to a predetermined condition. In accomplishing 
such a physical connection the actuating magnet may optionally be fixedly 
attached to an object which is to be protected by the device, or it may be 
fixedly attached to a stationary object. 
Provision is made to locate the magnetically operated switch device in a 
particularly desired place relative to the actuating magnet. Hence, the 
actuating magnet is preferably located withn a socket, while the 
magnetically operated switch is contained within a switch housing which 
fits slidably within the socket. A quantity of ferromagnetic material is 
attached to the outer end of the switch housing so that the switch housing 
may be magnetically held in the socket by the actuating magnet. 
Preferably, the socket and the switch housing are cylindrical and the 
ferromagnetic material is in the form of a soft iron collar attached to 
one end of the switch housing, while the electrical conductors are 
connected through the other end of the switch housing. 
A preferred magnetically operated switch for use in the device of the 
invention is a magnetic reed switch contained within the switch housing 
but located spaced slightly away from the soft iron collar attached to the 
end of the switch housing. When the switch housing is inserted into the 
socket far enough to bring the soft iron collar into proximity with the 
actuating magnet, a magnetic field is induced in and around the soft iron 
collar by the actuating magnet. This induced field causes the magnetic 
reed switch to actuate magnetically when the switch housing is located 
fully inserted in the socket. In a preferred embodiment, the socket is 
deep enough so that removal of the switch housing from the socket results 
in the magnetically operated switch moving far enough out of the magnetic 
field of the actuating magnet to allow the switch to become unactuated. 
When the device is in use the magnetic attraction between the actuating 
magnet and the soft iron collar retains the switch housing in its proper 
location within the socket. The magnetic force of attraction is sufficient 
to resist ordinarily expected forces such as those exerted on the 
conductor cable by vibration, wind, and normal motion of a movable object 
such as a boat at its mooring place, when an adequate length of cable is 
provided to accomodate normally expected motion. 
The actuating magnet may be secured in a desired location on a flat surface 
by fastening a mount holding only the actuating magnet in the desired 
location, while an outer housing which defines the socket fits over the 
magnet preventing access to the mount securing the magnet itself without 
prior removal of the outer housing. Removal of the outer housing in a 
mistaken understanding that its removal would also effect removal of the 
magnet results in displacement of the switch housing containing the 
magnetically operated switch from the actuating magnet's field. 
Consequently, the magnetically operated switch will become unactuated, 
providing an indication of an alarm situation to the alarm control system. 
To enhance the resistance of the device to tampering, a small biasing 
magnet may be located within the switch housing in a position close to the 
magnetically operated switch, thus magnetically actuating the switch 
whenever the switch housing is not located in a suitably strong, properly 
polarized magnetic field. The biasing magnet is situated relative to the 
magnetically operated switch so that its field opposes and balances that 
of the actuating magnet, as felt by the magnetically operated switch when 
the switch housing is properly located in the socket associated with the 
actuating magnet. The magnetically operated switch is therefore unactuated 
when the switch housing is properly located within the socket. The device 
of the invention is thus usable to provide a magnetically balanced 
open-loop alarm system circuit. In this form of the device, as well, the 
actuating magnet retains the switch housing within the socket by 
attracting the ferromagnetic material associated with the switch housing. 
It is therefore a principal objective of the present invention to provide a 
reliable electrical switch assembly for use in a security system theft 
detection circuit. 
It is another objective of the present invention to provide a connecting 
and sensing device for an electrical theft detection circuit of an alarm 
system which is not susceptible to adverse weather conditions. 
It is yet a further objective of the present invention to provide a method 
for detecting unauthorized movement of an object, including the steps of 
magnetically actuating a switch in an alarm circuit, magnetically 
retaining the switch in proximity to an actuating magnet, pulling the 
switch away from the actuating magnet in response to unauthorized movement 
of the object, and electrically detecting separation of the switch from 
the actuating magnet. 
It is an important feature of the present invention that it includes a 
magnetically operated switch contained in a switch housing and an 
actuating magnet located within a socket, adapted for receiving the switch 
housing, which requires removal of the magnetically operated switch from 
the field of the actuating magnet when the switch housing is removed from 
the socket. 
It is another important feature of the present invention that it includes a 
magnet holder assembly including a magnet mount for mounting the actuating 
magnet to the protected object, and a separate outer housing, defining the 
socket, which protectively covers the fasteners retaining the magnet 
mount, so that the magnetically operated switch is removed from the magnet 
field of the actuating magnet when the outer housing is removed from the 
object being protected. 
It is a principal advantage of the present device that it provides 
apparatus and a method in which a magnetically operated switch can be used 
to detect unauthorized movement of objects which need not be located as 
precisely as was necessary for use of previously known magnetically 
operated devices for this purpose. 
The foregoing objectives, features and advantages of the present invention 
will be more readily understood upon consideration of the following 
detailed description of the invention taken in conjunction with the 
accompanying drawings.

DETAILED DESCRIPTION OF THE INVENTION 
Referring now to FIG. 1 of the drawings, a connecting and sensing device 10 
embodying the present invention is shown being used to prevent undetected 
removal of a bicycle 12 from its proper location. Electrical conductors 
contained in a cable 14 connect the device 10 electrically to a control 
system 18 of an alarm system. Referring now also to FIG. 2, the cable 14 
of the connecting and sensing device 10 is preferably an armor protected 
cable, which contains at least a pair of electrical conductors 20 and 22, 
connected to a magnetically operated switch such as the encapsulated 
magnetic reed switch 24. The magnetic reed switch 24 includes a pair of 
flexible reed contacts 26 and 28 which are of an electrically conductive 
ferromagnetic material. 
The magnetically operated switch is fixedly located within a switch housing 
30 which may be of a cylindrical tubular shape and may be made of a 
suitably tough and rigid plastics material. Within the switch housing 30 
the encapsulated magnetic reed switch 24 and an end of the cable 14 may be 
securely fixed in place by a room temperature vulcanizing potting 
material. A quantity of a ferromagnetic material such as a soft iron 
collar 32 is fixedly attached to the switch housing 30, relatively close 
to the magnetic reed switch 24, and preferably at the outer end 34 of the 
switch housing 30. The reed contacts 26 and 28 and the collar 32 are all 
of ferromagnetic material having high permeability and low retentivity, so 
that magnetic fields are easily induced in them, yet quickly dissipate 
upon their removal from a magnetic field. 
An actuating magnet 36 is fixedly located within a magnet holder 38. The 
magnet holder 38 is generally cylindrical in shape, and includes external 
threads 40 along its length and a flange 42 located at an outer end 
thereof. A nut 44 may be held on the outside of the magnet holder 38 by 
the threads 40 to retain the magnet holder in a location extending 
inwardly through a structural member such as a wall 46, leaving the flange 
42 exposed. A threaded bore 54 is provided at the inner end 48 of the 
magnet holder 38 to receive a threaded bolt (not shown) for the same 
purpose, if desired. 
The actuating magnet 36 is located within a cavity such as a socket 50 
defined within the magnet holder 38, where it is fixed in place, as by 
adhesives. The socket 50 corresponds to the size of the switch housing 30, 
and is open through the flange 42 of the magnet holder 38, permitting the 
switch housing 30 to be slidably received therein with the collar 32 
adjacent to an end 52 of the actuating magnet 36. 
The cable 14, at a suitable distance from the switch housing 30, is fixedly 
secured within a bore 54 extending lengthwise through the magnet holder 38 
generally parallel with the socket 50. The conductors 20 and 22 extend 
rearwardly unarmored from the inner end 48 of the magnet holder 38, to 
connect the sensing device 10 of the present invention to the alarm 
control system 18. 
For example, the magnet holder 38 may be about 6 to 8 inches long and 1 
inch in diameter with the flange 42 being 11/2 inches in diameter. The 
socket 50 may be about 3/8 inch in diameter, with the switch housing 30 
being slightly smaller in diameter to provide an easily slidable fit. The 
switch housing 30 may be about 21/2 inches long and the collar 32 may be 
about 1/4 inch long, when a magnetic reed switch 24 is used as the 
magnetically operated switch of the device. The distance between the 
collar 32 and the switch 24 depends on the strength of the actuating 
magnet and the field strength needed to operate the switch 24. 
A connecting and sensing device 58 which is another embodiment of the 
present invention is disclosed in FIGS. 3 and 4. A magnet holder 60 of the 
device 58 includes a magnet mount 62. The magnet mount 62 defines a bore 
64 for receiving an actuating magnet 66 so that an end 68 is flush with a 
front face 70 of the magnet mount 62. An ear 72 extends from the front 
face 70 of the magnet mount 62 and includes a hole 74 for receiving a 
fastener such as a screw 76 to fasten the magnet mount 62 to a flat 
surface 78 of an object whose unauthorized removal is to be detected by 
the sensor 58. 
An outer housing 80, which is part of the magnet holder 60, includes a 
cavity 82 permitting the outer housing 80 to surround the magnet mount 62 
and be fastened to the same flat surface 78 to which the magnet mount 62 
is secured by the screw 76. A pair of flanges 84 and 86, located 
respectively along opposite sides of the outer housing 80, include holes 
88 for receiving fasteners to attach the outer housing 82 to the same 
surface 78 of the object being protected by the sensor 58, with the outer 
housing 80 covering the magnet mount 62. A tubular socket 90 is defined in 
the outer housing 80, with its longitudinal axis approximately parallel 
with the surface 78, in a location aligned with the bore or cavity 64. 
A switch housing 92 protectively contains a magnetically operated switch 
such as an encapsulated magnetic reed switch 94 which is electrically 
connected by a flexible cable 96 including electrical conductors (not 
shown), to a control circuit of an alarm system (not shown). As with the 
previously described switch housing 30, a collar 98, similar to the collar 
32, is fixedly attached to an outer end 100 of the switch housing 92. The 
socket 90 is of an appropriate size and shape to receive the switch 
housing 92, with the collar 98 adjacent to the end 68 of the actuating 
magnet 66 when the outer housing 80 is installed surrounding the magnet 
mount 62, as may be seen in FIG. 4. 
FIG. 5 discloses a connecting and sensing device 106 which is yet another 
embodiment of the present invention. The sensing device 106 includes a 
simple tubular cylindrical magnet holder 108. A radial flange 110 
including a pair of screw holes 112 is located at one end of the magnet 
holder 108 to enable it to be fastened easily to a portable object through 
the use of fasteners such as screws 114. An actuating magnet 116 is 
adhesively secured in the magnet holder 108, which defines an interior 
tubular socket 118 which may be approximately 1/4 inch in diameter and 3/4 
inch deep as measured between the end 120 of the actuating magnet 116 and 
the outer face of the flange 110. 
A switch housing 122 is of a correspondingly small size and is slidably 
receivable within the socket 118. A soft iron or other ferromagnetic 
collar 124 fixedly attached at one end of the housing 122 may be 3/16 inch 
in length. A small encapsulated magnetic reed switch 126 or other 
magnetically operated switch is retained within the interior of the switch 
housing 122 by suitable potting material, while electrical conductors 128 
and 129, connected with the terminals of the reed switch 126, extend 
outwardly from the end of the switch housing opposite the collar 124. 
Because of its small size the sensing device 106 is particularly well 
adapted for use with portable, pilferable items of high value such as 
television receiver sets and the like which are commonly provided in 
publicly accessible places. 
Operation of the connecting and sensing devices 10, 58 and 106 of the 
present invention will be better understood by referring additionally to 
FIGS. 6 and 7 which show, in a simplified, partially schematic manner, the 
way in which such a device operates. In FIG. 6 an encapsulated magnetic 
reed switch 130 of the normally open type is associated with a quantity of 
ferromagnetic material 132 which is equivalent to the collars 32, 98, and 
124. An actuating permanent magnet 134 provides a magnetic field which 
attracts the ferromagnetic material 132. Since the ferromagnetic material 
132 is fixedly located with respect to the reed switch 130, magnetic 
retention of the ferromagnetic material 132 adjacent to the end of the 
actuating magnetic 134 also physically retains the reed switch 130 in a 
known location relative to the actuating magnet 134. When the 
ferromagnetic material 132 is adjacent to the actuating magnet 134, a 
magnetic field, indicated schematically by lines of force 135, is induced 
in the ferromagnetic material 132, and extends around it and the reed 
switch 130, inducing a further magnetic field concentration in the 
magnetic reeds 136 and 138 of the switch 130, causing them to attract one 
another and flex into physical and electrical contact with one another. 
This closes the electrical circuit through the reed switch 130, so long as 
the ferromagnetic material 132 is located properly within a sufficiently 
strong magnetic field, such as that of the actuating magnet 134. 
Thus, when the switch housings of the previously described sensors 10, 58 
and 106 embodying the present invention are located within the sockets 50, 
90 and 118 of the respective magnet holders, so that the ferromagnetic 
collars 32, 98 and 124 are adjacent to the respective actuating magnets, 
the switches will be in a magnetically actuated state. This state of 
magnetic actuation can be detected electrically by a properly designed 
control circuit such as that of the alarm control system 18, when the 
device is electrically connected thereto. Removal of the switch housing of 
any of the above-described connecting and sensing devices from the socket 
(not shown in FIGS. 6 and 7, but functionally equivalent to the sockets 
50, 90 and 118) of the associated magnet holder, however, moves the 
respective reed switch and ferromagnetic material such as the collar 132 
so far from the magnetic field, such as that of the actuating magnet 134, 
that there is no longer a sufficiently strong induced magnetic attraction 
between the magnetic reeds 136 and 138 to maintain contact, and the 
elastic bias of the reeds 136 and 138 separates them from one another, 
breaking the electrical circuit, before the switch housing can be removed 
fully from the socket in which the actuating magnet is located. This 
operation is ensured by use of ferromagnetic material which has a high 
enough magnetic permeability to ensure that the field of an actuating 
magnet 135 extends through the ferromagnetic material 132 and induces a 
sufficiently strong field in the vicinity of the reed switch 130, and by 
ensuring that the magnetic retentivity of the ferromagnetic material 132 
is low enough so that the magnetism induced in the ferromagnetic material 
132 will be dissipated before the ferromagnetic material 132 and reed 
switch 130 have been completely withdrawn from the socket adjacent to the 
actuating magnet 134. 
The sensing device of the present invention may be installed in association 
with an alarm system circuit in several ways. First, the alarm system may 
be installed in a building, and the connecting and sensing device 10 of 
FIGS. 1 and 2 may be used by looping the cable 14 through or around a 
portion of the object to be protected against unauthorized removal, as 
shown with the bicycle 12 in FIG. 1. Alternatively, the alarm system might 
be mounted permanently on a movable object such as a motorcycle, and the 
cable 14 might be wrapped around an immovable object such as a lamp post 
when parking such a motorcycle. 
The magnet holder 60 is adapted to be mounted against a flat surface such 
as a surface 78 on the exterior of a freight container or a trailer truck 
box, while the cable 96 is connected to an alarm system permanently 
installed in an area where freight containers or the like are routinely 
parked. Unauthorized movement of a freight container once the switch 
housing 92 has been inserted into the socket 90 would be detected when 
movement of the container resulted in the cable 96 pulling the switch 
housing 92 from the socket 90, causing the switch 94 to become 
magnetically unactuated. An attempt to circumvent the sensing device by 
removing the magnet holder 60 from the freight container or trailer truck 
would also result in magnetic unactuation of the switch 94, since the 
magnet mount 62 is separately attached beneath the outer housing 80. 
Removal of the outer housing 80 from the freight container would cause 
displacement of the magnetically actuated switch 94 away from the 
actuating magnet 68 resulting in interruption of the magnetic actuation of 
the switch 94. 
Similarly, the switch housing 122 could be electrically and physically 
connected to a permanently installed alarm system. Removal of a portable 
object to which the magnet holder 108 is attached would result in the 
switch housing 122 being withdrawn from the magnet holder 108, causing the 
magnetic reed switch 126 to become unactuated. 
A higher-security embodiment of the sensing device of the invention, which 
is more difficult than the previously-described devices to circumvent with 
the use of additional magnets, is shown in a sectional view in FIG. 8. A 
switch housing 150, shown fragmentarily, includes a single-pole, 
double-throw, encapsulated magnetic reed switch 152 having a pair of reed 
contacts 154 and 156 which are of a ferromagnetic electrically conductive 
material, and a third reed 158 which is of a substantially non-magnetic 
electrically conductive material. The magnetic reed contact 154 is 
normally biased by its own elasticity into physical and electrical contact 
with the non-magnetic reed 158, in the absence of a magnetic field. A 
small biasing magnet 160, however, provides a magnetic field of sufficient 
strength to magnetically actuate the reed switch 152, bringing the 
magnetic reed contacts 154 and 156 into electrical contact with one 
another, in the absence of an opposing magnetic field of equal strength 
created by an external magnet such as the actuating magnet 158. A quantity 
of ferromagnetic material having high permeability and low retentivity, 
such as a soft iron collar 162, is fixedly attached to the switch housing 
150 and performs the same functions of physical retention and magnetic 
force field conduction as the ferromagnetic material 132 of FIGS. 6 and 7. 
A biasing magnet could be used similarly in any of the 
previously-described sensor devices 10, 60 or 106 according to the present 
invention, within the limitations of the physical size of the respective 
switch housing 30, 92 or 122. 
In the higher security device shown in FIG. 8, insertion of the switch 
housing into an appropriate socket results in a magnetic field being 
induced in the collar 160 by the magnetic field of the actuating magnet 
158. However, the actuating magnet 158 is stronger than the biasing magnet 
160 and is located in its magnet holder oriented to produce an opposite 
magnetic field felt by the magnetic reed contacts 154 and 156 with 
strength approximately equal to that of the magnetic field of the biasing 
magnet 160. This produces a net magnetic field in the vicinity of the 
magnetic reeds 154 and 156 which is too small to maintain magnetic 
actuation of the magnetic switch 152, and the reed 154 will be elastically 
moved into contact with the non-magnetic reed 158, producing an 
electrically detectable indication that conditions are normal. Attempts to 
use a hand-held magnet to imitate the actuating magnet, however, are 
unlikely to succeed, since too strong a magnetic field will overcome the 
biasing magnet 160 and close the magnetic reed contacts 154 and 156. 
It will be appreciated that, besides magnetic reed switches, other types of 
magnetically operated switches will also be usable in a sensing device 
according to the invention. For example, Hall effect magnetically operated 
semiconductor switching devices, or mercury-bellows type magnetically 
operated switches would also be useable herein. 
The terms and expressions which have been employed in the foregoing 
specification are used therein as terms of description and not of 
limitation, and there is no intention, in the use of such terms and 
expressions, of excluding equivalents of the features shown and described 
or portions thereof, it being recognized that the scope of the invention 
is defined and limited only by the claims which follow.