CA2301432C - Improved taut wire security system - Google Patents

Abstract

A taut wire security system and sensing apparatus having a sensor post with a number of individually mounted sensor modules. Each sensor module has a pivotally mounted sensor pin, and includes a sensor device for detecting movement of the sensor pin. A post controller associated with the sensor post scans each of the sensor modules connected to the post individually to determine if an alarm condition exists. The sensor devices include hall effect sensors for detecting motion of their respective sensor pin.

Description

IMPROVED TAUT WIRE SECURITY SYSTEM
This invention relates to a taut wire security system, and in particular to a sensing apparatus for sensing intrusions along a taut wire security fence.
Known taut wire security fences typically consist of a plurality of detection zones, with each detection zone comprising a pair of spaced anchor posts, a plurality of taut wires tensioned between the anchor posts by anchoring means, and a sensor post located between the anchor posts having mounted thereon a multiplicity of sensors, each of which is coupled to a taut wire. An inherent limitation of this type of known fence is that it is relatively insensitive to intrusions which occur close to the anchor post, i.e. such fences have a "dead zone" associated with each anchor post.
This problem is overcome by the taut wire security fence and sensing apparatus disclosed in U.S. patent No. 4,829,287 (Kerr et al) and U.S. patent No.
5,103,207 (Kerr et al). The fence sensing apparatus disclosed by Kerr et al comprises a plurality of detector posts, each of which includes anchor/sensor devices which both anchor the taut wire under tension and act as intrusion sensors. Although the security fence and sensing apparatus disclosed in the above patents possess a number of advantages over other systems, they require that a detector post be substantially disassembled in order to replace one or more of the anchor/sensor devices that comprise the detector post. Furthermore, such systems do not allow for remote individual monitoring of each of the anchor/sensor devices, so it is not possible to remotely identify which of a plurality of anchor/sensor devices of a detector post has failed when such failure occurs.
Furthermore, the sensing elements used disclosed in the above patents require physical contact between a sensing pin and the sensing element, which makes it difficult to isolate the sensing element from environmental affects.
Often times taut wire security systems will be, by their nature, located in hostile areas where it is desirable to effect repairs of any faulty components as quickly as possible in order to reduce the danger of an intrusion event occurring during any down time, and furthermore to reduce the amount of time that any service personnel are subject to the possibility of hostile attack.
Additionally, it is desirable that the replacement of faulty components can easily be carried out so that extensively trained personnel are not required to replace such components.
It is therefore desirable to provide an improved taut wire security fence having sensing apparatus which include anchor/sensor devices which can be easily and quickly replaced. It is also desirable to provide such a security system in which each of a plurality of anchor/sensor devices can be remotely monitored in order to individually identify which anchor/sensor device needs to be replaced without the need for personnel to perform any physical tests at the actual sensor post location. It is also desirable to provide a sensing element which is physically isolated from the sensor pin in order to allow the sensing element to be isolated from environmental affects.
The present invention is directed towards an improved sensing apparatus for use with a security fence including a plurality of taut tension wires.
According to one aspect of the invention, there is provided a sensing apparatus for use with a taut wire security system having a plurality of taut trip wires, comprising an elongate sensor housing post adapted to be rigidly anchored to the ground and a plurality of sensor modules individually removably mounted to the housing post. Each of the sensor modules has a pivotally mounted sensor pin with a forwardly extending end provided with a connector for attaching thereto a taut trip wire, and a sensing device for detecting motion of the sensor pin in response to force applied to the outwardly extending end thereof and generating a signal in response to the motion. The sensing apparatus includes a controller in communication with the sensor modules for detecting the signals generated by the sensing devices and generating an alarm. Preferably, releasable mounting clips mount the sensor modules to the sensor housing post. Conveniently, the controller can be operable to perform scan cycles during which it successively monitors each of the sensor modules individually. The sensing devices may each include magnetic means positioned in the pivot pin, and a Hall Effect sensor for monitoring the relative location of the magnetic means and outputting an electrical signal representative thereof.
According to a further aspect of the invention, there is provided a sensing apparatus for use with a taut wire security system including a plurality of trip wires, comprising an elongate sensor post adapted to be rigidly anchored to the ground, a plurality of sensor modules mounted to the sensor post, and a controller.
The sensor modules each have a pivotally mounted sensor pin having a first end provided with a connector for attaching thereto a taut trip wire, and a sensing device for detecting motion of the sensor pin in response to force applied to the outwardly extending end thereof and generating a sensor signal in response to the detected motion. The controller performs scan cycles in which it successively communicates with each of the sensor modules to individually monitor the sensor signals generated by the sensing devices thereof and provide an alarm if one or more of the sensing devices generate sensor signals indicating an alarm condition.
According to another aspect of the invention, there is provided a sensing apparatus for use with a taut wire security system including a plurality of taut trip wires, comprising an elongate sensor post adapted to be rigidly anchored to the ground, a plurality of sensor modules mounted to the sensor post and a controller.
The sensor modules each have a pivotally mounted sensor pin having an outwardly extending end provided with a connector for attaching thereto a taut trip wire, and an inwardly extending end having a magnet mounted therein, and a sensing device having a Hall Effect sensor for detecting motion of the sensor pin in response to force applied to the outward extending end thereof and generating a sensor signal in response to the motion. The controller is in electrical communication with the sensing devices and operable to generate an alarm if one or more of the sensing devices generate sensor signals indicating an alarm condition.

According to still a further aspect of the invention, there is provided a taut wire security system comprising a plurality of security fence sections and a central monitoring station. Each section comprises a plurality of taut wires extending between two upwardly extending detector posts anchored to the ground. Each of the detector posts includes a plurality of sensor modules mounted thereto each having a pivotally mounted sensor pin having a first end connected to one of the taut wires, and a sensing device for detecting the position of the sensor pin and generating sensor signals indicative of the position. Each detector post also includes a post controller in communication with the sensor modules and operative to monitor the sensor signals generated by each of the sensor devices and generate an alarm signal when the sensor signals indicate an alarm condition, the alarm signal including identification information for the post controller and the sensor module which generated the sensor signals indicating an alarm condition.
The central monitoring station is in communication with each of the post controllers to receive the alarm signals therefrom.
In the drawings:
Figure 1 is a plan view showing a section of a taut wire security fence system in accordance with the present invention;
Figure 2 is a partial perspective view of a sensing apparatus in accordance with the present invention;
Figure 3 is a block diagram of the controlling components of the taut wire security fence of Figure 1;
Figure 4 is a side view of a sensing apparatus in accordance with the present invention;
Figure 5 is a sectional top view of a sensor module mounted on a sensor post housing;
Figure 6 is a back view of the sensor module of Figure 5;
Figure 7 is a sectional top view of a sensor module mounted on a sensor post housing, showing an end-of line connection;

-$-Figure 8 is a perspective view of the sensor module of Figure 5 mounted to the sensor post housing;
Figure 9 is a circuit diagram of a sensing device of the sensing module of the present invention;
Figure 10 is a block diagram of a post controller of the present invention;
Figure 11 is a circuit diagram of a control circuit of the post controller of Figure 10;
Figure 12 is a circuit diagram of an isolation circuit of the post controller of Figure 10;
Figure 13 is a timing diagram showing exemplary timing of selected signals that are present during operation of the sensing apparatus of the present invention;
Figure 14 is a flow chart of the operation of a Reset and Scan Control Module of the post controller;
Figure 15 is a flow chart of the operation of a Sensor Post Scanning Module of the post controller;
Figure 16 is a flow chart of the operation of a Message Handler Module of the post controller; and Figure 17 is a front view of a monitor of a central monitoring station of the present invention.
With reference to Figure l, there is shown a plan view of a section of a taut wire security system, indicated generally by reference numeral 10 in accordance with the present invention. The taut wire security system 10 includes a series of horizontal taut trip wires 12 which are strung horizontally between detector posts 14. Separator posts 16 may be located between detector posts 14 to keep the taut wires 12 suitably spaced from each other.
With reference to Figure 2, each detector post 14 includes an elongate, vertically extending sensor post 18 and a support post 20. The sensor post 18 includes an elongate sensor housing post 22 to which are removably and individually attached a plurality of sensor modules 24. Each of the sensor modules 24 has a sensor pin 26 that is mounted to pivot in the horizontal direction.
Taut wires 12 are attached to the sensor pins 26 by tension springs 28 and ratchet tensioners 30. The support post 20 may conveniently comprise a cylindrical pipe set in a concrete base 32 which may be buried to provide additional stability to the detector posts 14. The sensor post 18 is preferably mounted to the support post 20 by a plurality of mounting brackets 34, which can be U-bolts.
Each of the sensor modules 24 includes a sensor for detecting motion of the sensor pin in response to force applied to the sensor pin, and generating an electrical signal that is indicative of such force. With reference to Figure 3, the sensors of the sensing modules 24 for each sensor post are electrically connected to a post controller, with each sensor post having its own post controller 36.
All of the post controllers for the taut wire security system are connected to a central monitoring station 38, and a central power supply 40.
The taut wire security system 10 is an intrusion detection system for protecting perimeters. The horizontal taut wires 12 are monitored for motion caused by such acts as cutting or climbing, which generates an alarm which is reported graphically and audibly at the central monitoring station 3 8.
The various components of the taut wire security system 10 will now be described in greater detail. Referring to Figures 1 and 2, sections of taut wire 12 run continuously from detector post 14 to detector post 14 without bends or breaks in the wires. The taut wires 12 are generally strung parallel to the ground with an inter-wire spacing between 2" and 6". The wires are supported by both the separator posts 16 and the detector posts 14.
Within each section of the security system, one end of the taut wires 12 are secured by tensioners 30, and springs 28 to sensor modules 24 of a sensor post 18.
The tensioners act like winches and are used to set the tension in the wire.
The other end of the wires are wrapped into loops 42 and secured by springs 28 to sensor modules on a different sensor post. It will be appreciated that Figure shows the taut wires 12 for two separate taut wire sections, with the looped ends _7_ 42 of the wires of one of the sections connected by springs 28 to the sensor modules 24, and the ends of the other section of taut wires 12 connected by tensioners 30 and tension springs 28 to sensor modules 24. Thus, the sensor pin 26 of each sensor module is acted on by the taut wires 12 of two sections of security fence. The taut wires 12 are tensioned such that each sensor pin 26 will be generally centered when no external forces are being applied to the taut wires connected to such pins.
The separator post 16 is a vertical support used to maintain a uniform wire spacing and to translate a vertical displacement of a taut wire 12 into longitudinal motion of the wire. A suitable separator post design is shown in U.S. patent No.

5,103,207 issued April 7, 1992 to Kerr et al.
With reference to Figures 4-8, the sensor post 18 of the present invention will now be described in greater detail. As noted above, the sensor post 18 includes a plurality of sensor modules 24 which are individually mounted to the sensor housing post 22. Figure 4 illustrates a sensing apparatus of the present invention, comprising a total of n sensor modules 24 mounted to sensor housing post 22, the sensor modules being designated as 24~,~-24~"~. The sensor modules 24~,~ to 24~n~ are arranged sequentially in daisy chain fashion with each sensor module being electrically connected to the one below it with a ten conductor ribbon cable 44 for carrying power, switching signals and sensor output. The top sensor module in the sequence, module 24~,~, and the bottom module in the sequence, sensor module 24~"~ are each connected by ribbon cables 46 and 48, respectively, to the post controller 36. The cables 44, 46 and 48 preferably run inside the sensor housing post 22 such that they are protected from the environment.
Figure 5 shows a top sectional view of one of the sensor modules 24 as mounted to sensor housing post 22. Sensor housing post 22 includes an elongate, upwardly extending back wall 50 and spaced-apart sidewalls 52 and 54. The back wall 50, and sidewalls 52, 54 define an elongate upwardly extending channel 56 _g_ into which each of the sensor modules 24~,~ to 24~n~ extends. As can be seen in Figure 5, the sensor modules 24~,~ to 24~n~ do not extend completely to the back wall 50, and thus a vertically extending passageway is provided along the back of the housing channel 56 through which the ribbon cables 44, 46 and 48 can pass.
Longitudinal outwardly extending flanges 58 and 60 are provided along the length of the sidewalls 52 and 54 to provide engagement surfaces for mounting clips 62 which are used to secure the sensor module 24 to the sensor housing post 22. The sensor housing post 22 is preferably constructed from extruded aluminum.
Each sensor module 24 includes a sensor body 64, which conveniently can be formed from extruded aluminum. The sensor body 64 has a front wall 66 that has an aperture formed through it for the sensor pin 26. The senor body 64 also includes spaced-apart sidewalk 68 and 70, which define, along with the front wall 66, an interior 72 of the sensor body 64. Preferably, a vertically extending pivot pin channel 74 is formed on the interior surface of the front wall 66 for receiving a pivot pin 76 which pivotally mounts the sensor pin 26 to the sensor body 64.
The sensor pin 26 is pivotally mounted by the pivot pin 76 such that it has an outwardly extending end 78 which can pivot horizontally as indicated by line 80.
The opposite end of the sensor pin 26 extends inwardly into the interior of the sensor body 64. Two magnets 82 with reversed polarity relative to each other are located in the inwardly extending end of the sensor pin 26.
The sensing module 24 further includes a sensing device 84 for sensing movement of the sensor pin 26. In particular, the sensing device 84 includes a Hall Effect sensor 86 which is mounted on a circuit board 88. The Hall Effect sensor 86 is located in the proximity of magnets 82 and is sensitive to changes in the magnetic field that occur due to movement of the sensor pin 26. The sensing device 84 includes additional electrical circuitry which will described in greater detail below. The circuit board 88 may conveniently be mounted in opposed grooves 90 that are provided along the sidewalls 68, 70 of the sensor body 64.
A
top end cap 103 (see Figures 7 and 8) formed from aluminum preferably extends across the top of the sensor body 64, and a bottom cap, also formed from aluminum, preferably extends across the bottom of the sensor body 64, thereby sealing the interior of the sensor body 72 from external elements. The interior 72 of sensor module 24 is preferably filled with a dielectric grease to assist in preventing water or other environmental irritants from entering the interior of the sensor body 72 and interfering with the operation of the sensing device 84.
The aperture through which the sensor pin 26 passes is preferably sealed by a neoprene grommet 92 which permits horizontal movement of the sensor pin 26, but restricts water from entering through the aperture.
In order to allow the sensing module 24 to be attached to the sensor housing post 22, L-shaped connecting flanges 94 are provided on each of the sidewalls 68 and 70. The L-shaped connecting flanges 94 define rearwardly opening channels for receiving the front ends of the sidewalls 52 and 54 of the sensor housing post 22. Two quick release mounting clips 62 are used to secure the sensing module 24 to the sensor housing post 22. The mounting clips 62, which are preferably made from spring quality stainless steel, have opposed ends 96 and 98 which are connected together by an intermediate portion 100. In use, one of the opposed ends 96 of one clip engages a ridge provided along the corner of L-shaped flange 94 of side wall 68 of the sensor body, and the other opposed end 98 engages the flange 60 on sidewall 54 of the sensor housing post 22. In a similar manner, the other clip 62 is used to secure the other side of the sensor module 24. Each of the sensing modules 24~~~ to 24~"~ are secured by two clips 62, which can easily be snapped on and snapped off of the sensor modules and the sensor housing post 22 in order to facilitate quick installation and removal of the individual sensor modules 24~,~ - 24~"~.
As can be seen in Figures 5 and 6, rearwardly extending header connectors 102A and 102B are provided on the backside of the circuit board 88. The electrical connectors 102A and 102B allow the ribbon cables 44 to be connected to the sensor modules 24. As can be seen in Figure 6, the connector 102A is located close to the upper portion of the sensor module 102, and the other connector 102B is located close to the lower portion of the sensor module 24.
The connectors 102A and 102B each preferably include recessed pins 104. Each of the ribbon cables 44, 46 and 48 preferably includes an electrical connector 106 having a plurality of pin receptacles for receiving the pins 104. Thus, the ribbon cables can be easily connected to and disconnected from the sensor modules 24 simply by inserting a friction fit connector 106 into a header connector 102A or 102B. As the cables 44 plug into header connectors 102A and 102B which are located on the backside of the sensor modules, in the interior of the sensor housing post 22, the cables are protected from direct exposure to the environment. The use of "plug-in", "pull-out" quick release connectors allows non-skilled personnel to individually quickly remove and replace faulty sensor modules.
As suggested above, the sensors are connected in daisy-chain fashion by the ribbon cables 44. In one preferred embodiment, the ribbon cables 44 are each 7" in length, which is long enough to span the distance between sensor modules for a wide range of taut wire spacing. In one preferred embodiment, each of the sensor modules 24 has a height of approximately 2", such that the spacing between taut wires is approximately 2" when the sensor modules 24 are located one above the other. Spacers (which can take the form of sensor bodies without any other components) can be placed in between the sensor modules in order to increase taut wire spacing if desired.
With reference to Figure 7, the connection detail for connecting springs 28 to sensor pin 26 will now be explained in greater detail. The outwardly extending end of the pin 26 preferably includes an outwardly opening threaded hole 79 for receiving a bolt 81. The bolt 81 passes through the ends of the springs 28 to secure them to the pin 26.
Figure 7 also illustrates the use of an anchoring device 93 which can be used when a particular sensor post is the last sensor post in a row of sensor posts.
For an end-of the-line sensor post, a single taut wire will be connected to sensor pin 26. The anchor device 93 counter balances the taut wire, thus allowing sensor modules 24 to be used, without modification, on the end-of the-line sensor post. In order to facilitate use of the anchor device 93, the sensor body 64 is configured so that sideways opening channels 97 are provided between outwardly extending portions of the front wall 66 and the rest of the sensor body. The anchor device 93 includes one tension spring 28 and an L-shaped securing member 95, arranged in a generally U-shaped configuration. One end of the spring 28 is attached to a first end 99 of the securing member 95, and the other end of the spring 28 is attached by bolt 81 to the sensor pin 26. A second end 101 of the securing member 95 is slidably received within one of the channels 97.
Referring now to Figure 9, a circuit diagram of a preferred embodiment of a sensing device 84 is shown. Each of the sensing modules 24~,~ to 24~"~ has its own sensing device 84. As noted in Figure 9, the first and second header connectors 102A and 102B are each ten pin connectors. For each of the sensor modules 24~,~ to 24~"_,~, the bottom connector 102B is connected by a ribbon cable section 44 to the top connector 102A of the next lowest sensor module 24~2~ to 24~"~, respectively. The top connector 102A of the first sensor module 24~,~
is connected directly to the post controller 36 by ribbon cable 46, and the bottom connector 102B of the last sensor module 24~"~ is connected directly to the post controller 36 by ribbon cable 48. The ribbon cables 44 connect like numbers i.e.
pin 1 of connector 102A of module 24~n~ is electrically connected to pin 1 of connector 102B of module 24~"-1~, and so on.
The sensor post 18 is arranged so that the post controller 46 can perform scan cycles during which it sequentially monitors the sensing devices 84 of each of the sensing modules 24~1~ to 24~n~. Preferably, the sequential monitoring is performed in alternate upward and downward scan cycles in which the post controller propagates through the sensor modules from top to bottom, and then bottom to top, alternatively.

As shown in Figure 9, the sensing device 84 of each sensor module includes a Hall Effect Sensor 86; transistors 108 and 110; J-K flip flops 112A
and 112B (which can be packaged together on a dual flip flop chip having local power circuitry 112C); resistors 114, 116, 118, 120 and 122; capacitor 124; and diode 126.
Each sensor device 84 is powered by a 5 volt power supply provided by the post controller 36. When a particular sensing device 84 is selectively monitored by the post controller 36, power is supplied to its Hall Effect Sensor 86, which causes the Hall Effect Sensor 86 to output an analog voltage proportional to the magnetic field intensity that it senses. This analog signal, which is indicative of the position of the sensor pin 26 associated with the sensing device 84, is output on the SIG signal line of the sensor device 84. The SIG signal lines of each of the sensor devices 84 are connected together to form a common conductor for communicating analog Hall Effect sensor output signals to the post controller.
In order to allow the multiple sensor modules to share a common signal line, the post controller and sensor modules are configured so that the sensor modules each use the signal line during a unique time slot during the scan cycle. Thus, each sensing module 24~, ~ to 24~"~ effectively has an "on" state when power is supplied to its Hall Effect Sensor 86, and an "ofp' state during which no power is supplied to its Hall Effect Sensor. Transistor 108, and J-K flip flops 112A and 112B control the operation of the Hall Effect Sensor such that the sensing device 84 operates in the following manner. When a signal is asserted on the SRST (sensor reset) line, the Hall Effect Sensor 86 will be forced off. The SRST line is common to all of the sensor modules 24~,~ to 24~n~, and allows the post controller 36 to simultaneously reset all the sensing devices 84 that make up the sensor post 18.
Each sensing device 84 can be turned on either by 1 ) asserting a signal on its SUP (sensor up) line and pulsing the SCLK (sensor clock) line, or by 2) asserting a signal on the SDOWN (sensor down) line and pulsing the SCLK line.
When the sensing device 84 is turned on in the first manner noted above (i.e.
as a result of a signal on its SUP line), its JK Flip Flop 112B will assert the UPEND
line of the sensing device (which is connected to the SUP line of the next highest module in the sequence). When the sensing device 84 is turned on by the second manner noted above (i.e. as a result of a signal on its SDOWN line) its JK
Flip Flop 112A asserts the DEND line of the sensing device (which is connected to the SDOWN line of the next lowest sensor module in the sequence). Once sensing device 84 has been turn on by either of the above two events, it is turned off by the occurrence of the next pulse on the SCLK line. Such a configuration allows the "on" state to propagate sequentially across the sensing modules 24~,~ to 24~"~ in either the "up" direction or in the "down" direction with each SCLK clock signal.
As will be explained in greater detail below, transistor 110 and resistor 114 provide a means by which the post controller can verify correct operation of the sensor modules 24~,~ to 24~"~.
The post controller 36 is a micro-controller-based unit which is preferably housed in a fiberglass enclosure mounted on the support post 14. As noted above, the post controller is connected to the top and bottom sensor modules by ribbon cables, which carry the switching signals for controlling the sensor modules 24~,~
to 24~"~. The post controller 36 puts out signals to switch on the sensor modules one at a time sequentially until the entire sensor post 18 is read, first top to bottom, then bottom to top. The controller 36 not only detects and communicates alarms, but also determines and reports faulty sensors and mis-wiring, over a twisted pair network to the central monitoring station 38, preferably using the LonTalk (trademark) network protocol.
With reference to Figure 10, the post controller 36 preferably comprises three main circuits, namely a control circuit 126, an isolation circuit 128, and a local power supply circuit 130. Conveniently, the control circuit, isolation circuit and power supply circuit can each be implemented on separator circuit boards connected together by a back plane. The power supply circuit 130 converts 120 VAC or 240 VAC, received over the system bus from system power supply 40, to two isolated 5 volt supplies, one of which supplies the sensor modules 24~, ~ -24~"~, and the other of which supplies the local circuitry of the post controller 36.
Figure 11 illustrates one preferred embodiment of the control circuit 126, and Figure 12 illustrates one preferred embodiment of the isolation circuit 128.
The isolation circuit 128 provides electrical isolation for all signal lines that must be linked between the control circuit 126 and the sensor modules 24~,~ -24~"~. In particular, the isolation circuit 128 includes an A to D convertor U13 for converting analog signals received from the sensor modules into digital signals that are provided to the control circuit 126. Optic isolators U3-U10 optically isolate signals passing through the isolation card 128 to and from the control circuit 126.
The control circuit 126 includes a twisted pair control module U 15 which contains a micro-controller that controls the sensing device logic and interprets sensing device feedback. The control module U 15 also contains a transceiver, which sends and receives information over the security system network to and from the central monitoring station 3 8. The control module U 15 contains the software for controlling the operation of the sensor post, and stores parametric information, such as an identity number for the post controller, the number of sensor modules attached to the sensor post, and the sensing device sensitivity. The control module U 15 monitors the Hall Effect signal generated by the sensor devices on a sensor module by sensor module basis and determines if a signal goes outside of a preset sensitivity window for a predetermined number of signal readings. If so, the control module U 15 reports an alarm with the sensor module position (numbering down from the top of the sensor post), the identity of the sensor post, the current signal reading and the expected signal reading. The acceptable signal reading range is determined at system start-up and is periodically updated to overcome environmental effects. The wider the range of the sensitivity window, the less sensitive the fence is to motion.
With reference to Figures 12 and 9, Table 1 below sets out the connection details between the isolation circuit 128 of the post controller and the sensor modules of the sensor post 18. In particular, the first column lists the signal lines of the isolation circuit. The second column identifies the respective lines of the sensor device 84 of the sensor module 24~,~ to which the indicated isolation circuit lines are connected by means of ribbon cable 46. The third column indicates the signal lines of the sensor device 84 of the top sensor module 24~"~ to which the indicated signal lines of the isolation circuit are attached via ribbon cable 48.
Table 1: Connection Details Between Isolation Circuit and Sensor Modules Isolation Circuit Sensor Module 24,1; Sensor Module 24,"~
SCLK SCLK SCLK
SRST SRST SRST
SUP SUP
SDOWN SDOWN
VNU VNU
VND
SIG SIG SIG
DEND DEND
UPEND UPEND
The sensing device 84 of each of the sensor modules 24~,~ - 24~"~ includes a resistor 114 and transistor 110 for providing feedback to the post controller concerning proper switching operation. In particular, the resistor 114 of each sensing device 84 provides one link in a resistive ladder of 100 ohm resistors.
Both ends of the resistive ladder are connected to the post controller. From both ends, a Wilder current sink (shown generally by reference numeral 132 in Figure 12) sinks 1mA of current. Whenever a sensing device 84 is on, its transistor places a 5 volt voltage in series with its resistor 114. Thus, in the case of a upward scan, the voltage on the VNU line at the isolation circuit will be a function of the number of sensor modules that are located between the sensor module that is currently being monitored, and the bottom sensor module 24~"~. For example, if the fourth sensor module from the bottom is being monitored during an upward scan, the resistive ladder will have a total resistance of the series combination of four resistors 114, and such information can be interpreted by the control module U

so that it can identify the specific sensor module that it is currently monitoring.
Conveniently, the resistor 114 of each of the sensing devices 84 can have a resistance of 100 ohms, such that with a Wilder current source of 1 mA the addition of each resistor to the resistive ladder will result in approximately an incremental 0.1 volt drop. As the post controller sequentially moves up the post, the voltages observed at the Wilder current sink steps incrementally, and the post controller registers a number of 0.1 volt drops corresponding to the number of sensor modules that have already been monitored during the scan cycle. Thus, in the case of an upward scan, the voltage on the VNLJ line acts as location index, and in the case of a downward scan, the voltage on the VND line acts as location index. The information is used by the post controller to verify that the sensor module switching is proceeding correctly. In the event that the voltage index drops in the middle of a post scan, to a level that indicates there are no sensors "on", the post controller reports a maintenance alarm to the central monitoring station with the post identity, and the identity of the affected sensor module. Similar maintenance alarms are reported in the event that the voltage index stops changing during the scan, which indicates that a sensor has not turned "ofp' Figure 13 illustrates a exemplary timing diagram showing the digital output signals SRST, SCLK and SUP of the post controller 36, and the analog input signals VNLT and SIG to the post controller 36 during an upward scan of the bottom seven sensor modules 24~"~ - 24~".~~ of the sensor post 18. Plotted line 134 indicates the incremental decreases nV in the index signals VNU as the post controller works its way up the sensor modules 24~"~ to 24~~~~. By keeping track of the magnitude of the index signal VNU, (and VND in the case of a downward scan) the post controller 36 is provided with feed-back that permits it to identify which sensor module it is currently monitoring. The post controller 36 also keeps track of which sensor module it is communicating with by counting SCLK pulses.
The feed-back provided by the VNLJ and VND index signals allows the post controller 36 to verify that the sensor modules are switching in the expected manner and allows identification of faulty sensor.
With reference to Figure 13, and the flow charts shown in Figures 14, 15 and 16, the control software of the post controller will now be described in greater detail.
Figure 14 illustrates the steps of a reset and scan control module136 of the control software. Figure 15 illustrates the steps in a sensor post scanning module 138 of the software, and Figure 16 illustrates the steps performed by a message handler module 140 of the software.
The post controller 36 is configured such that the control module U15 begins the reset and scan control software module 136 upon power on, or after it has been reset (step 142). 'The control module U15 can be reset remotely from the central monitoring station 38 or locally by placing a conductor across jumper J3 of the control circuit 126.
Subsequent to a power on or reset occurring, light emitting diode LED2 is turned on (step 144) to provide a visual indication that the post controller is active. Next, the control module checks to see if it can properly communicate with the AID converter U13 (steps 146 and 148). In the event that it is unable to communicate with the A/D converter, the control module will report a hardware initialization error (step 1 SO) to central monitoring station 3 8, and will thereafter inhibit scanning and only process incoming messages (step 152).
In the event that the communications check between the control module U 15 and the AID converter U 13 yields positive results, the control module U

will reset its scan count to zero (step 154). A baseline reset flag is then set to indicate that new baselines are not required (step 155). (As will be discussed in greater detail below, baselines are values obtained and stored by the post controller in respect of the sensor modules 24~,~ to 24 ~"~ against which future sensor device signal readings are compared to determine if an intrusion alarm has occurred). A scan timer is then set to 100 ms (step 156). The control module then checks to see if the scan timer has expired, or if the number of scan cycles is less than three (step 158). If the scan timer has not expired and the number of scan cycles is three or greater, then the control module will check for messages (step 160) by implementing message handler module 140. However, if the scan timer has expired, or the number of completed scan cycles since power on or post controller reset is less than 3, then the control module will chose a scan direction, either up or down, whichever is the opposite of the last scan performed (step 162), and then implement the sensor post scanning module 138 (step 164). It will be noted that the reset and scan control module 136 is configured to ensure that two scan cycles are performed prior to implementing message checking step 160 .
This is to allow the post controller 36 to initialize by obtaining initial readings from each of the sensor modules 24~,~ to 24~"~ for both an upward scan cycle and a downward scan cycle.
With reference to Figure 15, the scan post module 138 will now be explained. As a first step in scan post module 138, the post controller 36 turns off all sensor modules 24~1~ to 24~"~ by pulsing the SRST (sensor reset) line (step 168).
The post controller then checks the voltage index (VNU during an up scan, or VND during a down scan) to see if any sensors modules are on by comparing the voltage index to a predetermined threshold value, which in one preferred embodiment is 0.8 volts. In the event that any of the sensor modules are on (i.e.
index signs VNLJ or VND>0.8V), then the post controller 36 reports a maintenance alarm to the central monitoring station 38 (step 170) during the first cycle in which the problem is discovered.
The post controller 36 then prepares to turn on the first sensor module by asserting the SUP line of sensor module 24~"~ (in the event of an upward scan), or by asserting the SDOWN line of sensor module 24~,~ (for a downward scan) (step 172). The sensor post then turns on the first sensor module in the scan cycle by pulsing the SCLK (sensor clock) line. After providing a clock pulse on the SCLK
line, the post controller resets the SUP or SDOWN line (depending on whether or it is performing an upward or downward scan) to ensure that the initial sensor in the scan cycle will turn off with the next SCLK pulse (step 174).
The post controller will then check to see if the initial sensor module in the scan cycle has indeed been turned on by checking to see if the voltage index VNU
exceeds a predetermined threshold in the case of an upward scan, or the voltage index VND exceeds a predetermined threshold in the event of a downward scan.
In the event that the post controller 36 determines the initial sensor module has not been turned on and that it has not previously reported such a problem, it will send a maintenance report to the central monitoring station 38 indicating that the sensor module has failed to turn on (step 176). The post controller then will check to see if all the sensor modules are off by checking to see if the appropriate voltage index VNU or VND is less than a predetermined threshold (step 178). In the event that all sensors are off, the post controller will send a report to the central monitoring station advising that all sensor modules are off (step 180), abort the scan cycle (step 182), and return to the reset and scan control software module 136. In the event that a sensor module is on, the post controller 36 will proceed from step 178 to read the SIG line signal output from the Hall Effect Sensor for the sensor module that is currently on (step 184). In order to ensure that the sensor module being monitored is operating properly, the measured signal is evaluated to ensure that it falls within a predetermined range that the post controller would expect the signal from a properly operating sensor module to fall within. In the event that the measured signal falls outside the predetermined range, a maintenance alarm is sent to the central monitoring station (step 186). Such maintenance alarm will only be sent once for a specific sensor module.
The post controller then checks to see if the measured signal falls inside or outside of a predetermined non-alarm range (step 188). In particular, the post controller will compare the measured signal from the "on" sensor module to see if it falls outside of non-alarm range which is defined by a predetermined baseline plus/minus a predetermined sensitivity value. Preferably, the post controller maintains a scan history in which it stores, for each sensor module, the results of the comparison between the measured signal and the non-alarm range for the last sixteen scan cycles. Thus, as part of step 188, the post controller sets a flag in the scan history indicating whether the measured signal fell inside or outside of the non-alarm range. In the event that the number of scans since power on or reset of the post controller is greater than two and the measured signal from the sensor module has fallen outside of the non-alarm range for a predetermined number of scans, then the post controller will report an intrusion alarm to the central monitoring station 38 (steps 190 and 192). The intrusion report will include identification of the post, as well as the particular sensor module which has triggered the alarm. The post controller 36 will then inhibit subsequent intrusion alarms for the alarm generating sensor, module so that it does not repeatedly send intrusion alarm signals to the central monitoring station once the central monitoring station has been notified of the problem (step 194). The fact that the post controller bases its decision to report an intrusion alarm on the measured signal from more than one scan minimizes number of false alarms due to transient elements such as wind.
After determining if an intrusion alarm must be reported, and reporting the intrusion alarm if necessary, the post controller 36 sets the baselines for the sensor modules 24 ~~~ to 24~n~ if required (step 196). In particular, the post controller 36 checks to see if a baseline reset flag has been set to indicate that a baseline reset is required, and if so resets the baselines for each of the sensor modules 24~,~ -24~"~, on a sensor module by sensor module basis, to the greater Hall Effect Sensor signal reading taken for each of the respective sensors during the last two scan cycles. As noted below the baseline reset flag is controlled by the central monitoring station 38.

Next, the post controller executes the message handler module 140 (step 198). After checking for messages, the post controller checks to see if it is at the final sensor in its scan sequence. If so, it checks to ensure that, in the case of an upward scan, that the UPEND line of the sensor module 24~,~ has been activated, and in the case of a downward scan that the DEND line of the sensor module 24~~~
has been activated. If not it will report, during the first scan cycle in which it detects the problem, a maintenance alarm to the central monitoring station (step 200).
The post controller 36 will then turn off the current sensor module and switch to the next sensor module, by pulsing the SCLK line (step 202) after which it determines if the scan is complete by comparing a counter that it keeps of scanned sensor modules against the total number of sensor modules in the sensor post (step 204). In the event that the scan is complete, the post controller checks to see if all of the sensor modules are off by determining if the appropriate voltage index signal VNU or VND is below a predetermined threshold value, and generates a maintenance alarm the first time that it determines that all sensors are not off at the conclusion of a scan cycle (step 206). After performing step 206, the post controller exits the scan module 138 and returns to the reset and scan control module 136 (step 208).
In the event that the scan cycle is not complete, after performing step 204, the post controller 36 checks to ensure that at least one sensor module is on by comparing the appropriate voltage index VNL1 or VND to ensure that it exceeds the predetermined "on" threshold (step 210). In the event that no sensor modules are on, the post controller reports a maintenance alarm to the central monitoring station the first time it detects such an error (step 212), and aborts the scan cycle, thereby returning to the reset and scan control module 136 (step 214).
In the event that a sensor module is on, the post controller 36 checks to see that the appropriate index voltage VNLT or VND has advanced by one sensor module, and reports a maintenance alarm the first time that it detects that the voltage index has not advanced by the appropriate amount (step 216). Once the sensor post controller 36 has determined whether the voltage index has advanced by the appropriate amount, it then proceeds to measure the signal for the current sensor module (step 184) and repeats the steps 186-216 noted above until the scan cycle is either completed (step 208) or aborted (step 214).
With reference to Figure 14, upon exiting the sensor post scanning module 138, and returning to the reset and scan control module 136, the post controller checks to see if the scanning module 138 was exited either because the scan was aborted, or because the scan cycle was properly completed (step 218). In the event that the scan was aborted, the post controller immediately attempts to perform the scan cycle in the opposite direction to which it was being performed in, and accordingly it sets the scan flag to the opposite of what it was set at, and proceeds with returning to the sensor post scanning module 138 (step 220). It will be understood that an aborted scan is most likely the result of faulty sensor or failed electrical connection (perhaps the result of a cut ribbon wire), and by reversing the scan direction the post controller is able to complete the scan cycle from the opposite direction, thereby working around the faulty sensor module or failed electrical connection. After performing a reverse direction scan, if required, or if such a scan were not required, the post controller 36 checks to see if the scan cycle which it just performed was the second scan cycle since reset or power-on occurred (step 222). In the event that it is the second scan, the post controller performs an initialization routine in which it sets the base line value for each of the sensor modules 24~1~ to 24~"~ based upon the measured values for the sensor modules obtained during the first two scan cycles (which will include an up scan cycle and a down scan cycle). In particular, the base line for each sensor module is set to the higher of the up or down reading for that particular sensor module during the first two scan cycles (step 224). After completing step 222 (and step 224 if necessary) the post controller increments the scan counter by one, and sets the scan timer to 500 ms (steps 226 and 228), after which it returns to step and repeats the steps noted above.
It will thus be appreciated that after the post controller is reset or powered on, it performs an initialization routine during which it performs an up scan and a down scan to obtain base line values for each of the sensor modules. After the initialization routine is complete, the post controller will execute the message handler module 140 to check for messages (step 160). The post controller will continue to check for messages until the scan timer expires, after which it will execute the sensor post scanning module (steps 162 and 164). Thus, under normal operation, a scan cycle will be performed approximately every 500 ms.
With reference to Figure 16, the message handler module 140 will now be described. T'he first step performed in the message handler module 140 is to determine if any messages have been received by the post controller 36 from the central monitoring station 38 (step 219). If no messages have been received, the post controller returns to the previous module that it was running (step 231 ). If a message has been received; the post controller checks to see if the message type is to "assign a new post number" (step 233). If so, the post controller checks to see if the logical address in the message data matches that of the post controller (step 235). If so, the post controller resets its post number to that specified in the message data (step 237), otherwise it discards the message (step 239), and returns to the previous software module. If the message type is not a new post number assignment, the post controller determines if the message is addressed specifically to it (rather than to another one of the post controllers) (step 230). If the message is not addressed to it, the post controller discards the message (step 228) and returns to the previous software module. If the message is directed towards the post controller, it launches one or more of a number of possible sub-routines based on the message type (step 232). As indicated in Figure 15, the message can be of several different types. One possible message type is a "heart beat"
message in which the central monitoring station 3 8 simply sends a request to the post controller to identify itself, and to which the post controller responds by sending its post number (step 234). Heart beat messages allow the central monitoring station 3 8 to pole each of the post controllers that are connected to it to ensure that they are active and in communication with the central monitoring station.
The central monitoring station 38 can also send a baseline reset message to which the post controller 36 responds by setting the baseline reset flag (step 236) so that the next time step 196 of the sensor post scanning module 13 8 is executed, the post controller will reset baselines for each of the sensor modules 24~,~ -24~n~
by setting each sensor module baseline to the highest reading obtained from that sensor for the last two scan cycles. Periodically resetting the baselines allows the post controller to adjust for changes in temperature and other conditions that may occur during operation of the security fence, and in one exemplary embodiment a baseline reset signal is sent approximately every ten minutes.
The central monitoring station 38 can also send out a sensitivity value update signal to the post controller to set the sensitivity window surrounding the baseline values, thereby defining the non-alarm range for each of the sensor modules (step 238). The controller can also transmit a reset message to the post controller 36, thereby causing post controller to restart its reset and scan control module at step 142 (step 240). The post central monitoring station 38 can also send a set intrusion scan signal to configure the number of readings required to fall outside of the non-alarm threshold range to result in an intrusion alarm being reported (step 242). The set intrusion scan data is used by the post controller in step 190 of the sensor post scanning module 138.
In order to configure the post controller, the central monitoring station 3 8 can send a "number of sensors" signal advising the post controller of the number of sensor modules mounted to its sensor post 18 (step 244).
The central monitoring station 3 8 can also send a "post status request"
message, in response to which the post controller 36 will respond with various parameters concerning the sensor post, such as for example its post number and the number of sensor modules it has (step 246).

The post controller 36 can also send out a sensor status request signal (to which the post controller 36 will respond by sending sensor module parameters and data, which can include for example the current baseline for each of the sensor modules) (step 248). The sensor parameters, such as the baseline can be compared by the central monitoring station 38 against predetermined values to determine and identify potential maintenance problems.
In one preferred embodiment, the central monitoring station 38 is implemented using a personal computer, which is connected by a network to each of the post controllers 36. The central monitoring station 38 monitors each of the post controllers 36 and is configured to generate audible and/or visual alarms in the event that the central monitoring station receives either a maintenance or intrusion alarm from one of the post controllers. Alarms can be reset and silenced by authorized system operators. All system events, such as start-up, alarm resets and sensitivity adjustments are logged to a hard drive of the central monitoring station 38. With reference to Figure 17, in a preferred embodiment the central monitoring station 38 is configured to display a plan view 250 of the protected site on a monitor 252. The plan view includes identification of each of the separate zones ( i.e. sections) of the security fence. In such a preferred embodiment, when an alarm is received at the central monitoring station it triggers an audible alarm and flashes the zone where the alarm has occurred on the plan view 250. The sound of the audible alarm and the color of the flashing zone will depend on whether the alarm is a maintenance alarm or an intrusion alarm.
It will be appreciated that not all of the features of the preferred embodiment disclosed above need be adopted in a sensor post apparatus. For example, in some embodiments strain gauges could be used in place of the Hall Effect Sensors as sensing elements. Of course, as strain gauges require physical attachment of the sensing element to the sensor pin, it would be more difficult to isolate strain gauges from environmental effects than Hall Effect Sensors. In some embodiments, the sensor modules may not be individually removable from the sensor post.
It will be appreciated that the circuitry disclosed above in respect of the sensor devices and the post controller could take a wide variety of different configurations and still perform the same function. Accordingly, the circuit diagrams in Figures 9, 1 l and 12 are merely one preferred embodiment of a number of possible embodiments: of such circuits. The following table provides a list of exemplary components for the circuits of Figures 9, 11 and 12, which will function to allow up to 40 separate sensor modules on a post:
TABLE 2:
Reference No. Comt~onent Value-Model #
86 Hall Effect Sensor Honeywell ~ 55495A
102A,102B dual row straight-pin headers with shroud 112 A, B,C dual J-K flip-flop package Motorolla ~ 4027 114 resistor 100 SZ t 1 116, 11$, 120, 122 resistors 4.7 K each 124 capacitor 0.1 ~cF
U15 twisted pair control module Echelon ~ 55020-lo~/~r-lOF
with flash memory Atmel ~ AT29C512=90J 1 TABLE 2:
Reference No. Comt~onent Value-Model #

Ul low voltage inhibitor U2A-U2E inverters, hex Schmitt triggers S3, S4 surge arrestors C 1 capacitor 220 pF

C11 capacitor .l,u F 50 V

R1, R2 resistors 330 S2 C3,C4,CS,C12,C13 capacitors .l,u F 50 V

C2 capacitor 39 pF

R3, R5 resistors 3.92K 1% 1/4 W

~i R4, R6 resistors 120 S~

R7 resistor 18K 1/4W

Rg resistor 330 SZ

R9 resistor 560 SZ

RN 1 (RN 1 A-RN resistor network 7x330 SZ
1 G) RN2 (RN2A-RN2G) resistor network 7x560 S2 RN3 (RN3A-RN3E) resistor network 5 x 47K

RN4 (RN4A-RN4E) resistor network 5 x 47K

U3-U10 optic isolators U 11, U 12 inverter, hex Schmidt triggers U13 10 bit, 11 channel AID MC 145050P
converter As will be apparent to those skilled in the art in the light of the foregoing disclosure, many alterations and modifications are possible in the practice of this invention without departing from the spirit or scope thereof. The foregoing description is of the preferred embodiments and is by way of example only, and is not to limit the scope of the invention.

Claims (27)

1. A sensing apparatus for use with a taut wire security system having a plurality of taut trip wires, comprising:
an elongate sensor housing post adapted to be rigidly anchored to the ground, a plurality of sensor modules individually removably mounted to said housing post such that each individual sensor module can be demounted from said housing post without moving the other sensor modules, each of said sensor modules having a pivotally mounted sensor pin with an extending end provided with a connector for attaching thereto a taut trip wire, and a sensing device for detecting motion of said sensor pin in response to force applied to the extending end thereof and generating a signal in response to the motion;
a plurality of mounting clips removably mounting said sensor modules to said sensor housing post; and a controller in communication with said sensor modules for detecting the signals generated by said sensing devices and generating an alarm.

2. The sensing apparatus of claim 1 wherein each of said sensor modules has a sensor body with an interior and a front wall having an aperture therethrough, said sensor pin being pivotally connected to said sensor body by a pivot pin and extending forwardly through the aperture, a rearwardly extending end of said sensor pin and said sensor device being located in the interior of said sensor body.

3. The sensing apparatus of claim 2 wherein said sensor housing post has a back wall with spaced apart side walls extending forwardly therefrom, said back wall and side walls defining an elongate channel, at least a portion of the interior of each said sensor bodies being located within the elongate channel of said housing post when said sensor modules are mounted thereto.

4. The sensing apparatus of claim 3 wherein an elongate outwardly extending flange is provided along each of the sensor housing post sidewalk, and each of said sensor bodies has a pair of opposed sidewalk each having an outwardly extending flange thereon, said flanges providing anchoring surfaces for said mounting clips.

5. The sensing apparatus of claim 4 wherein said mounting clips are formed from resilient material, and each include an intermediate portion connecting first and second spaced apart opposed clip ends, one of said ends engaging the flange of one of the sensor post sidewalk, the other of said ends engaging the flange of one of the sensor body sidewalk of one of the sensor modules, each of said sensor modules being mounted to said sensor post housing by two of said mounting clips.

6. The sensing apparatus of claim 3 wherein each of said sensor modules includes opposed sidewall portions spaced closer together than the sensor post sidewalk, each sidewall portion having formed thereon an outwardly extending connecting flange defining a rearwardly opening channel into which is slidably received a part of one of the sensor post sidewalk.

7. The sensing apparatus of any one of claims 2 to 6 wherein the interiors of said sensor bodies are filled with a dielectric grease to minimize penetration of external elements therein.

8. The sensing apparatus of any one of claims 1 to 7 wherein said sensor modules are electrically connected to receive and send signals to said controller in a daisy chain configuration wherein each sensor module is connected by electrical cable to an adjacent sensor module, with at least one of the sensor modules being connected by electrical cable to the controller.

9. The sensing apparatus of any one of claims 1 to 8 wherein the sensing devices each include a Hall Effect sensor for monitoring the relative location of a magnetic means located in the pivot pin and outputting an electrical signal representative thereof.

10. The sensing apparatus of claim 9 wherein said Hall Effect sensors are electrically connected to provide sensor signals to the controller along a common conductor, said controller and said sensor modules being operable to perform scan cycles during which the controller individually and successively monitors the Hall Effect sensor of each of said sensor modules, the controller successively causing each said Hall Effect sensor to momentarily turn on and generate on the common conductor a signal indicative of sensor pin location.

11. A sensing apparatus for use with a taut wire security system including a plurality of trip wires, comprising:
an elongate sensor post adapted to be rigidly anchored to the ground;
a plurality of sensor modules mounted to the sensor post, each having (a) a pivotally mounted sensor pin having a first end provided with a connector for attaching thereto a taut trip wire, and a second end, and (b) a sensing device for detecting motion of the sensor pin in response to force applied to the first end thereof and generating a sensor signal in response to the detected motion; and a controller performing scan cycles in which it successively communicates with each of said sensor modules to individually monitor the sensor signals generated by the sensing devices thereof and provide an alarm if one or more of the sensing devices generate sensor signals indicating an alarm condition.

12. The sensing apparatus of claim 11 wherein the controller stores a predetermined baseline reference value for each of the sensing devices and compares the stored baseline reference values with the sensor signals generated by the sensing devices during each scan cycle to determine if movement of any sensor pins has occurred.

13. The sensing apparatus of claim 12 wherein the controller is operative to occasionally reset the stored baseline reference values based on recent sensor signals generated by the sensing devices.

14. The sensing apparatus of any one of claims 11 to 13 wherein the controller is operative to detect and identify faulty sensor devices by comparing the sensor signals generated by the sensing devices to predetermined criteria.

15. The sensing apparatus of any one of claims 11 to 14 wherein said sensing devices are connected sequentially by electrical cables, with the first sensing device in the sequence being directly connected by electrical cable to the controller, and each of the second to penultimate sensing devices being connected by electrical cables to the previous sensing device in the sequence.

16. The sensing apparatus of claim 15, wherein each sensing device is configured to transmit a unique voltage index signal to the controller when.
being monitored thereby, the controller being configured to identify each sensing device based on its unique voltage index signal.

17. The sensing apparatus of claim 16 wherein the last sensing device in the sequence is also directly connected by electrical cable to the controller, and the controller is configured to perform forward scan cycles in which it individually monitors the sensing devices starting from the first sensing device and ending with the last sensing device, and reverse scan cycles in which it individually monitors the sensing devices starting from the last sensing device and ending with the first sensing device.

18. The sensing apparatus of claim 17 wherein each of said sensing devices includes a resistor, said sensing devices being connected to each other such that the resistors thereof form a chain of serially connected resistors, said sensing devices each having switch means for placing a voltage on the chain of serially connected resistors at the sensing device when the sensing device is being monitored, the potential at an end of said resistor chain providing said voltage index signals.

19. The sensing apparatus of claim 18 wherein the controller is responsive to the voltage index signals to detect when the electrical connection between adjacent sensors is broken and modify the scan cycles to avoid the broken electrical connection.

20. The sensing apparatus any one of claims 11 to 19 wherein magnets are positioned on the second ends of the sensor pins, and the sensing devices each include a Hall Effect sensor for monitoring the position of the sensor pin associated therewith and generating an electrical signal indicative of its position.

21. The sensing apparatus of claim 20 wherein said Hall Effect sensors are electrically connected to provide sensor signals to the controller along a common conductor, said controller being operable to individually and successively monitor the Hall Effect sensor of each of said sensor modules during said scan cycles by successively causing each said Hall Effect sensor to momentarily turn on and generate on the common conductor said electrical signal.

22. The sensing apparatus of any one of claims 11 to 21 wherein the sensing apparatus comprises part of a security system having a plurality of the sensing apparatus, the controller of each sensing apparatus being connected to a central monitoring station which is operative to receive alarm and identification information from each of the controllers.

23. A sensing apparatus for use with a taut wire security system including a plurality of taut trip wires, comprising:
an elongate sensor post adapted to be rigidly anchored to the ground;
a plurality of sensor modules mounted to the sensor post, each having (a) a pivotally mounted sensor pin having a first end provided with a connector for attaching thereto a taut trip wire, and a second end having a magnet mounted therein, and (b) a sensing device having a Hall Effect sensor for detecting motion of the sensor pin in response to force applied to the first end thereof and generating a sensor signal in response to the motion; and a controller in electrical communication with each of said sensing devices and operable to generate an alarm if one or more of said sensing devices generate sensor signals indicating an alarm state.

24. The sensing apparatus of claim 23 wherein said Hall Effect sensors are electrically connected to provide sensor signals to the controller along a common conductor, said controller and said sensor modules being operable to perform scan cycles during which the controller individually and successively monitors the Hall Effect sensor of each of said sensor modules, the controller successively causing each said Hall Effect sensor to momentarily turn on and generate on the common conductor a sensor signal indicative of sensor pin position.

25. A taut wire security system comprising:
a plurality of security fence sections, each section comprising a plurality of taut wires extending between two upwardly extending detector posts anchored to the ground, each of said detector posts including (a) a plurality of sensor modules mounted thereto each having a pivotally mounted sensor pin having a first end connected to one of said taut wires, and a sensing device for detecting the position of the sensor pin and generating sensor signals indicative of the position;
and (b) a post controller in communication with the sensor modules and operative to monitor the sensor signals generated by each of said sensor devices and generate an alarm signal when the sensor signals indicate an alarm condition, the alarm signal including identification information for the post controller and the sensor module which generated the sensor signals indicating an alarm condition; and a central monitoring station in communication with each of the post:
controllers to receive the alarm signals therefrom.

26. The taught wire security system of claim 25 wherein each post controller determines and stores baseline values against which to compare the sensor signals generated by the sensor devices monitored thereby to determine if an alarm condition exists.

27. The taut wire security system of claim 26 wherein the central monitoring station is operative to send out periodic polling signals to the post controllers, and the post controllers are operative to respond to the polling signals by sending information about the baseline values stored thereby to the central monitoring station.