CA1273428A - Intrusion detection apparatus - Google Patents
Intrusion detection apparatusInfo
- Publication number
- CA1273428A CA1273428A CA000543720A CA543720A CA1273428A CA 1273428 A CA1273428 A CA 1273428A CA 000543720 A CA000543720 A CA 000543720A CA 543720 A CA543720 A CA 543720A CA 1273428 A CA1273428 A CA 1273428A
- Authority
- CA
- Canada
- Prior art keywords
- signal
- subsonic
- generating
- frequency
- response
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
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Classifications
-
- G—PHYSICS
- G08—SIGNALLING
- G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
- G08B13/00—Burglar, theft or intruder alarms
- G08B13/16—Actuation by interference with mechanical vibrations in air or other fluid
- G08B13/1654—Actuation by interference with mechanical vibrations in air or other fluid using passive vibration detection systems
- G08B13/169—Actuation by interference with mechanical vibrations in air or other fluid using passive vibration detection systems using cable transducer means
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- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Burglar Alarm Systems (AREA)
Abstract
ABSTRACT
Apparatus for detecting intruders in an off-limits area, such as a railway track bed, comprises vibration means and signal analyzing means. The vibration pick-up means picks up vibrations caused by intruder contact and generates an electrical signal correlatable with such vibrations. The signal analyzing means includes selecting means for selecting a subsonic portion of the signal, and measuring means for measuring one or more parameters of the subsonic portion and for generating an alarm signal. The vibration pick-up means preferably comprises a coaxial cable coupled to a row of contact plates each supported on resilient support means and tuned to resonate in response to subsonic driving frequencies caused by human beings falling onto or walking on the contact plates.
Apparatus for detecting intruders in an off-limits area, such as a railway track bed, comprises vibration means and signal analyzing means. The vibration pick-up means picks up vibrations caused by intruder contact and generates an electrical signal correlatable with such vibrations. The signal analyzing means includes selecting means for selecting a subsonic portion of the signal, and measuring means for measuring one or more parameters of the subsonic portion and for generating an alarm signal. The vibration pick-up means preferably comprises a coaxial cable coupled to a row of contact plates each supported on resilient support means and tuned to resonate in response to subsonic driving frequencies caused by human beings falling onto or walking on the contact plates.
Description
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FIELD OF THE INVENTION
This invention relates to apparatus for detecting intruders in an off-limits area and for generating an alarm signal in response thereto, and in particular, to apparatus for generating a signal for activating the braking system of an approaching train in response to passengers falling or jumping into the path of the train.
BACKGROUND OF THE INVENTION
In the case of train passenger platforms, it is not generally feasible to place an immovable physical barrier such as a fence between the platform and the train tracks, since passengers must necessarily cross the plane of such a barrier when entering and exiting trains. The inevitable result is that injuries and deaths occur when passengers fall from passenger platforms onto the tracks below into the path of an approaching train. The number of deaths caused by such incidents, be they accidents, suicides or murders, is surprisingly high. In the case of one subway system servicing a large metropolitan area in North America, passengers are hit and killed by subway trains on the average of about one passenger per week. Accordingly, there is at present a need to reduce the number of deaths and injuries caused by passengers falling from passenger platforms into the paths of approaching trains.
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Automatic emergency train stop systems have the potential to be more reliable and to have a better response time than manual systems employing a brakeman situated at the front of a train. Moreover, automatic emergency stop systems are essential in the case of fully automated driver-less trains, such as those used in some light rapid -transit systems. However, known automated emergency stop systems have not proved to be effective. For example, existing level crossing systems, utilizing floating boards resting on an array of microswitches which trigger depending upon the weight incident thereon, are very costly to maintain and prone to false alarms such as those caused by a gradual build up of snow. Other systems, relying upon light beams or microwaves, have been proposed for use as emergency stop systems for driver-less trains, but these systems in many cases must be turned off as the train approaches the station, or while the train is in the station, to prevent false alarms caused by the train itself and passengers entering and exiting the train. As a result, such light beam or microwave systems tend to be ineffective in preventing accidental deaths resulting, for example, from visually-impaired passengers mistaking the gaps between adjacent passenger cars for the open car doors. Prior art systems also tend to be relatively ineffective at distinguishing between intrusions caused by human beings and other objects.
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SUMMARY OE THE INVENTION
The present invention is directed towards apparatus for detecting intruders in an off-limi-ts area, and for generating an alarm system in response -thereto. Such apparatus comprises vibration pick-up means located in the off-limits area for picking up vibrations caused by an intruder coming into contact therewith and for generating an electrical signal correlatable with such vibra-tions, and signal analyzing means for analyzing the electrical signal generated by the vibration pick-up means, including selecting means for selecting a subsonic portion of the signal within a predetermined subsonic frequency range, measuring means for making a measurement of at least one preselected parameter of the subsonic portion of the signal and for generating an alarm signal depending upon the outcome of the measurement.
The vibration pick-up may comprise at least one flexibly mounted contact surface which vibrates in response to being con-tacted by an intruder, and conversion means coupled to the contact surface for converting mechanical vibrations of the contact surface into an electrical signal.
The contact surface is preferably suppor-ted on resilient support means, wherein the resiliency of the support means is selected such that the contac-t surface has a natural frequency within a pre-selected subsonic frequency range.
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Such subsonic frequency range is preferaby selected to include frequency nodes corresponding to human beings falling on and walking on the contact surface.
A preferred embodiment of the invention is directed towards apparatus for activating the braking system of an approaching train in response to intrusions into the path of the train by human beinqs. Such apparatus comprises a series of horizontally disposed contact plates mounted in the path of the train on resilient support means, a noisy coaxial cable mechanically coupled to the con-tact plates for moving in response to vibrations of the contact plates and for generating an elec-trical signal correlatable therewith, means for filtering and processing such signal, and means for generating an alarm signal.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described, by way of example only, with reference to the following drawings, in which like numerals refer to like parts, and which:
Figure 1 is a perspective view of a preferred embodiment of the intrusion detection apparatus of the present invention.
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~.~734~3 Figure 2 is an exploded perspective view of the vibration pick-up means of the preferred embodiment;
Figure 3 is a block diagram of one embodiment of the signal analyzing means of the present invention;
Figure 4 is a graph showing the frequency response of the signal analyzing means of the present invention; and Figure 5 is a circuit diagram of another embodiment of the signal analyzing means of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
As illustrated in Figure 1, the intrusion detection apparatus of the invention includes vibration pick-up means 2 and signal analyzing means 3. Vibration pick-up means 2 comprises two rows 4, 5 of vibratory contact plates 6, mounted in a generally horizontal orientation, and a coaxial cable 8 for converting vibrations of the plates into correlatable electrical signals coupled to each row of plates 6. Row 4 of plates 6 is situated between passenger platform 7 and running rail 9, and row 5 of plates 6 is situated between running rail 9 and running rail 11. Contact plates 6 are preferably thin, rectangular plates constructed from a hard material such as fibreglass reinforced rigid urethane foam. Cables 8 extend the length of rows 4,5, and are attached to each plate 6 of a particular row by .:.:: :. : - :- : :., . . -:
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cable clips 12. Each of contact plates 6 is independently mounted on resilient support means shown generally as 14, so as to move independently of each other.
Referring now to ~igure 2, resilient support means 14 includes rigid supports 15 upon which are mounted resilient blocks 16. Plate brackets 17 are mounted under the corners of contact plate 6 and are adapted to secure resilient blocks 16 to plates 6. Resilient blocks 16 are described in more detail below.
Coaxial cables 8 are "noisy" cables, i.e. badly made coaxial cables having a relatively loose centre conductor 18.
When such a cable is moved, centre conductor 18 moves relative to the outer conductor 19, creating an induced voltage signal. It has been found that this "noise" signal is correlatable with the vibration o* the cable; that is, if the cable is vibrated at a subsonic frequency, the "noise" signal includes a component at the same subsonic frequency. A large resistor is placed across the center and outside conductors 18, 19 of each of cables 8 so that induced voltage causes a current to flow through cable 8. A
coaxial cable is preferred because it produces a relatively reproducible electrical signal in response to physical movement of the cable, but alternatives, such as a twisted pair of wires running the length of the plates, could be used in place of a coaxial cable.
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The present inventor has recognized that when a humanbeing jumps or falls onto, walks on, or otherwise comes into relatively sharp and sudden contact with contact plates 6, vibrations are created. These vibrations tend to have a fairly broad-band frequency spectrum. However, the present inventor has analyzed this frequency spectrum, and has found that it invariably includes major frequency nodes in the sùbsonic frequency range, i.e. frequencies below about 15 Hz.
In particular, a human being dropping onto the contact plates 6 from a height of about l meter creates one frequency node at about 10-ll Hz and another at about 3 Hz. The lO Hz node is believed to be caused by the human being bouncing upon impact.
The frequency of this collision or "bounce" node frequency is dependent upon the speed of impact of the human being, which in turn is dependent upon the height of the passenger platform relative to the surface of the contact plates. The 3 Hz node is believed to reflect the inhomogeneous nature of a human being -upon impact, compressible flesh vibrates relative to incompressible bones, at a frequency of about 3 Hz. It might be therefore said that human beings have a natural frequency of 3 Hz, since human flesh vibrates at such frequency in response to a sudden impact. Thus it has been found that collisions between a human being and contact plates cause vibrations which include a collision frequency node dependant upon the height of the passenger platform and a natural frequency node of about 3 Hz.
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In addition, when a human being walks or runs on contact plates 6, an additional subsonic frequency node is created. In the case of walking, the node tends to be around 1-2 Hz, the walking frequency of a human being, because as a human being walks on the plates, a periodic thrust having a horizontal component is imparted to the contact plates. Obviously, typically running frequencies for human beings will be somewhat higher than walking frequencies.
In order to ensure that all of the above subsonic signature frequency nodes are picked up by (i.e. imparted to) vibration pick-up means 2, contact plates 6 must be capable of readily vibrating at such subsonic frequencies. In other words, the natural frequency of vibration pick-up means 2 itself must be in the subsonic range, so that resonance will occur when vibration pick-up means is subjected to driving forces in the subsonic range. This is achieved by mounting contact plates 6 on resilient support means 14, so that contacting plates are free to move a considerable distance back and forth in response to subsonic driving frequencies. It will be appreciated that considerable "displacement" of contact plates 6 is needed in order for the subsonic vibrations of interest to be imparted there, because if contact plates 6 were solidly mounted, the subsonic vibrations of interest would be mechanically attenuated, since the natural frequency of a solidly mounted plate would be well into the sonic range. In the preferred embodiment, ,, ' '~ ~
resilient blocks 16 are blocks of closed eell urethane foam about 1 3/8 inch in thickness, having a density enabling them to be compressible to about 3/8 inch. Thus the "displacement" of the resiliently mounted contact plates 6 is about 1 inch~ However, it will be appreciated that other types of resilient supports, such as springs with a suitable k constant, could be used instead of urethane blocks.
Referring now to Figure 3, signal analyzing means 3 of one embodiment of the present invention comprises filtering means 25, measuring means 26, and alarm generating means 35. Filtering means 25 amplifies the portion of the cable signal within the subsonic frequency range of interest and attenuates the portions of the cable signal outside such frequency range. Filtering means 25 comprises preamplifier 27, band pass filter 28, and line preamplifier 29. Preamplifier 27 is an operational amplifier whieh amplifies the cable signal by a factor of about 5 to 1, and whieh has a cut-off frequency of about 20 Hz. Band pass filter 28 attenuates those frequency components of the cable signal 21 which are outside the subsonic frequencies of interest, by a faetor of about 100 to 1. Line preamplifier 29 amplifies the output of band pass filter by a factor of about 40 to 1, and has a eut-off frequency of about 12 Hz.
7~L~S~3 Figure 4 illustrates the frequency response of filtering means 25, which acts like a low pass filter having a cut-off at about 7 or 8 Hz. It should be noted that filtering means 25 does not completely filter out the 10 Hz human collision frequency node, because this collision frequency node tends to be of considerably higher amplitude than the human natural frequency node at 3 Hz.
Referring again to Figure 3, filtered and amplified signal 30 is fed into measuring means 26, comprising Schmitt trigger 32 and pulse length separator 33. Schmitt trigger 32 reacts to the value of the slope of the leading edge of incoming signal 30. If the slope is above a pre-selected value, Schmitt trigger 32 triggers, i.e. it changes state from high to low value, or vice versa. Pulse length separator 33 measures the length of time that the Schmitt trigger 32 remains latched in a particular state. If the latching time is greater than a pre-determined time as discussed in detail below, an alarm signal 34 is generated by pulse length separàtor 33.
It should be noted that noisy coaxial cable 8 picks up not only the subsonic vibration signals of interest, but also various background signals in other frequency ranges, including a 60 Hz spike caused by nearby 60 cycle electrical equipment, a signal on the order of 600 Hz produced by the wheels of the ...... : .' -, . ~ , :
approaching -train interacting with the rails, and higher frequency audible signals caused by passengers talking. Thus, as noted above it is necessary to filter the cable signal by filtering means 25, with a view to removing signals outside the subsonic range of interest. However, band pass and cut-off filters are not perfect. Signals outside the cut-off frequency which are several orders of magnitude greater in amplitude than the signals of interest will be attenuated, but not completely eliminated. Therefore, filtered signal 30 will from time to time include high frequency spikes which trigger Schmitt trigger 32.
To avoid false alarms caused by such high frequency spikes, the output of Schmitt trigger 32 is monitored by pulse length separator 33. High frequency spikes are of very short duration, so they cause the Schmitt trigger 32 to stay latched for only a short period of time, whereas a true subsonic signal causes Schmitt trigger 32 to stay latched for a relatively long period of time. Therefore, pulse length separator 33 is designed to generate an alarm signal only i~ Schmitt trigger 32 stays latched for more than a pre-determined latching time. The latching time period is controlled by an adjustable resistor, which is field adjustable to suit the particular application. If a fast response time is necessary, as is the case with the emergency stop system of the preferred embodiment, the latching time should be made as short as possible without causing too many false alarms. It has been found that a latching time of about 1/4 second is a good compromise for many applications.
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Alarm signal 34 is then fed into alarm generating means 35, which may include a timer and relay drive 36, various relays 37 and an sonalert driver circuit 38. Timer and relay drive 36 includes a timer which latches for a relatively long set time of approximately 2 seconds, in response to the relatively short alarm signal 34, in order to produce an appropriate signal for driving relays 37.
The present invention may also include monitoring equipment, such as chart recorder for measuring the signals produced at various points in the circuitry. As shown in Figure 3, filtered and amplified signal 30 is split up and fed into chart recorder 40, which is used to calibrate the sensitivity of the system.
Figure 5 is a schematic diagram of the presently preferred embodiment of signal analyzing means 3. Vibration of cable 8 produces an electrical signal across resistor 22 which typically includes the subsonic frequency nodes of interest as well as higher frequency components including very high amplitude transients. The output of cable 8 is applied to operational amplifier 41, which converts the high impedence signal from cable 8 to a low impedence output signal. Operational amplifier 41 acts as an amplifier and filter in that it amplifies the subsonic frequency nodes of interest by a factor of up to 10 to 1 and .. ...
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attenuates higher frequency signals by a factor of up to 10 to 1.
Potentiometer 42 controls the gain of operational amplifier 41.
The output of operational amplifier 41 is supplied both to broken sensor circuit 60, explained in more detail below, and to low pass filter 43. Low pass filter 43 is a fourth order filter comprising four operational amplifiers 44, 45, 46 and 47, which are connected in series to give an attenuation factor of 24 db per octave. The cut off frequency of low pass filter 43 is about 8 Hz. Low pass filter 43 filters out all high frequency components of the signal, except for very high amplitude transients. The output of low pass filter 43 is applied to diode 48, which removes the positive voltage component of the signal.
Diode 48 is connected to transient suppressor circuit 49, comprising adjustable resistor 50 and capacitor 51, which removes the high amplitude, high frequency transients from the signal, because such transients are not of sufficient duration to discharge capacitor 51. The output of transient suppressor circuit 49, which now consists solely of the subsonic frequency nodes of interest, is supplied to visual display circuit 52 and to monostable circuit 53.
Monostable circuit 53 comprises a 555 monostable multivibrator 54, which triggers when the input signal drops below a given threshold voltage. Alarm duration circuit 55 adjusts the duration of the output of monostable multivibrator 54 . ;. ,: ::.. : : . i ~
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from 1 to 10 seconds. The output of monostable multivibrator 54 drives LED 56 and turns off a transistor 57, which is normally in an "on" state. Transistor 57 opens relay 58, which in turn drives alarm circuit 59. Transistor 57 is kept in a normally ~on" state, so that an alarm condition will be generated in the event of a power failure.
Broken sensor circuit 60 creates an alarm condition in the event that cable 8 is cut or otherwise broken. Broken sensor circuit 60 comprises comparator 61, one input of which is kept at a constant reference voltage by voltage divider 62. The other input of comparator 61 is connected to the output of operational amplifier 41. When cable 8 is cut, the amplitude of the output of operational amplifier 41 becomes greater than the reference voltage, causing comparator 61 to prcduce an output signal. This output signal drives LED 63 and turns off transistor 57, causing relay 58 to open.
In operation, when a passenger comes into contact with one or more of vibratory contact plates 6, such contact will create vibrations over a broad-band frequency spectrum. Included in that spectrum are certain subsonic frequency nodes characteristic of human intruders, as discussed above. These subsonic frequency nodes act to "drive" the vibratory contact plates. Because the natural frequency of the contact plates is close to the driving frequency, the plates will resonant at such ..
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~3 driving frequency. Since the coaxial cable is mechanically coupled to contact plates 6, the resonance of the contact plates will cause coaxial cable 8 to vibrate in unison. As the inner conductor of cable 8 moves relative to the outer conductor, and electrical signal having frequency nodes in the subsonic range, correlatable with the subsonic vibrations of the contact plates, is created. This electrical signal is first filtered by signal analyzing means 3 to remove, to the extent possible, all components of the cable signal outside a subsonic frequency range of interest. The amplitude of the filtered signal is then measured. If a true subsonic signal of sufficient amplitude is detected, signal analyzing means 3 will generate an output alarm signal indicative of an alarm condition. Otherwise, no alarm signal will be generated.
The response time of the subject intrusion detection apparatus is relatively fast, about 1/4 second. Accordinglyj when used as an emergency train stop system, use of the present invention has resulted in the capability of stopping a driver-less electric light rapid transit train, approaching a passenger platform at approximately 30 miles per hour in braking mode, within 40 meters. This would mean, in the case of a passenger platform of 80 meters in length, that if an intrusion into the train path occurs in the middle portion of the platform just as -the front of the train reaches the front of the platform, it would be possible to stop a train before it reaches the point -. : - . ........ . .
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P~3~3 of intrusion. It will be appreciated, however, that the s-topping distance will vary with the effectiveness of the train's braking system and other external factors.
The present invention is not limited to detecting only human intruders, but rather it is designed to detect other objects which are large enough to damage a train. The apparatus of the present invention can detect the presence of dogs and other relatively large animals on the tracks because a collision between such animals and contact plates 6 produces both natural frequency nodes and collision frequency nodes which are in the subsonic frequency range monitored by signal analy~ing means 3.
The presence on train tracks of various types of heavy inanimate objects, such as boulders, can also be detected by the subject -apparatus, even though these objects do not exhibit the phenomenom of body components vibrating relative to each other upon sudden impact, because such objects still exhibit a subsonic collision or bounce frequency dependant upon the height of the fall. Thus the apparatus of the present inven-tion could be adapted for installation on sections of tracks extending under overpasses several meters high, by tuning the apparatus to monitor a collision frequency correlatable with the height of the overpass.
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Furthermore, the intruder detection apparatus of the presen-t invention is not limited to emergency train s-top systems.
It could be used as an interface between the public and a variety of other off-limits areas which are not adapted to be secured by a physical barrier. For example, a series of contact plates could be laid down around the periphery of a docked ship and on the gang-plank, in such a way that unauthorized persons attempting to enter the ship would necessarily have to walk on the contact plates.
It will also be apparent that the embodiments of the invention disclosed herein could be computerized by digitizing the output of the coaxial cable or the output of the signal filtering means. This digitized signal could then be processed by microprocessor based signal processing means. For example, reference values for various parameters could be stored in the ROM (Read Only Memory) of a microcomputer, and then the microcomputer could be programmed to compare the current values of such parameter against the reference values thereof.
Accordingly, while the present invention has been described and illustrated with respect to the preferred embodiments, those skilled in the art will appreciate that numerous variations of the preferred embodiments may be made without departing from the scope of the invention, which is defined in the appended claims.
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FIELD OF THE INVENTION
This invention relates to apparatus for detecting intruders in an off-limits area and for generating an alarm signal in response thereto, and in particular, to apparatus for generating a signal for activating the braking system of an approaching train in response to passengers falling or jumping into the path of the train.
BACKGROUND OF THE INVENTION
In the case of train passenger platforms, it is not generally feasible to place an immovable physical barrier such as a fence between the platform and the train tracks, since passengers must necessarily cross the plane of such a barrier when entering and exiting trains. The inevitable result is that injuries and deaths occur when passengers fall from passenger platforms onto the tracks below into the path of an approaching train. The number of deaths caused by such incidents, be they accidents, suicides or murders, is surprisingly high. In the case of one subway system servicing a large metropolitan area in North America, passengers are hit and killed by subway trains on the average of about one passenger per week. Accordingly, there is at present a need to reduce the number of deaths and injuries caused by passengers falling from passenger platforms into the paths of approaching trains.
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Automatic emergency train stop systems have the potential to be more reliable and to have a better response time than manual systems employing a brakeman situated at the front of a train. Moreover, automatic emergency stop systems are essential in the case of fully automated driver-less trains, such as those used in some light rapid -transit systems. However, known automated emergency stop systems have not proved to be effective. For example, existing level crossing systems, utilizing floating boards resting on an array of microswitches which trigger depending upon the weight incident thereon, are very costly to maintain and prone to false alarms such as those caused by a gradual build up of snow. Other systems, relying upon light beams or microwaves, have been proposed for use as emergency stop systems for driver-less trains, but these systems in many cases must be turned off as the train approaches the station, or while the train is in the station, to prevent false alarms caused by the train itself and passengers entering and exiting the train. As a result, such light beam or microwave systems tend to be ineffective in preventing accidental deaths resulting, for example, from visually-impaired passengers mistaking the gaps between adjacent passenger cars for the open car doors. Prior art systems also tend to be relatively ineffective at distinguishing between intrusions caused by human beings and other objects.
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SUMMARY OE THE INVENTION
The present invention is directed towards apparatus for detecting intruders in an off-limi-ts area, and for generating an alarm system in response -thereto. Such apparatus comprises vibration pick-up means located in the off-limits area for picking up vibrations caused by an intruder coming into contact therewith and for generating an electrical signal correlatable with such vibra-tions, and signal analyzing means for analyzing the electrical signal generated by the vibration pick-up means, including selecting means for selecting a subsonic portion of the signal within a predetermined subsonic frequency range, measuring means for making a measurement of at least one preselected parameter of the subsonic portion of the signal and for generating an alarm signal depending upon the outcome of the measurement.
The vibration pick-up may comprise at least one flexibly mounted contact surface which vibrates in response to being con-tacted by an intruder, and conversion means coupled to the contact surface for converting mechanical vibrations of the contact surface into an electrical signal.
The contact surface is preferably suppor-ted on resilient support means, wherein the resiliency of the support means is selected such that the contac-t surface has a natural frequency within a pre-selected subsonic frequency range.
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Such subsonic frequency range is preferaby selected to include frequency nodes corresponding to human beings falling on and walking on the contact surface.
A preferred embodiment of the invention is directed towards apparatus for activating the braking system of an approaching train in response to intrusions into the path of the train by human beinqs. Such apparatus comprises a series of horizontally disposed contact plates mounted in the path of the train on resilient support means, a noisy coaxial cable mechanically coupled to the con-tact plates for moving in response to vibrations of the contact plates and for generating an elec-trical signal correlatable therewith, means for filtering and processing such signal, and means for generating an alarm signal.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described, by way of example only, with reference to the following drawings, in which like numerals refer to like parts, and which:
Figure 1 is a perspective view of a preferred embodiment of the intrusion detection apparatus of the present invention.
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~.~734~3 Figure 2 is an exploded perspective view of the vibration pick-up means of the preferred embodiment;
Figure 3 is a block diagram of one embodiment of the signal analyzing means of the present invention;
Figure 4 is a graph showing the frequency response of the signal analyzing means of the present invention; and Figure 5 is a circuit diagram of another embodiment of the signal analyzing means of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
As illustrated in Figure 1, the intrusion detection apparatus of the invention includes vibration pick-up means 2 and signal analyzing means 3. Vibration pick-up means 2 comprises two rows 4, 5 of vibratory contact plates 6, mounted in a generally horizontal orientation, and a coaxial cable 8 for converting vibrations of the plates into correlatable electrical signals coupled to each row of plates 6. Row 4 of plates 6 is situated between passenger platform 7 and running rail 9, and row 5 of plates 6 is situated between running rail 9 and running rail 11. Contact plates 6 are preferably thin, rectangular plates constructed from a hard material such as fibreglass reinforced rigid urethane foam. Cables 8 extend the length of rows 4,5, and are attached to each plate 6 of a particular row by .:.:: :. : - :- : :., . . -:
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cable clips 12. Each of contact plates 6 is independently mounted on resilient support means shown generally as 14, so as to move independently of each other.
Referring now to ~igure 2, resilient support means 14 includes rigid supports 15 upon which are mounted resilient blocks 16. Plate brackets 17 are mounted under the corners of contact plate 6 and are adapted to secure resilient blocks 16 to plates 6. Resilient blocks 16 are described in more detail below.
Coaxial cables 8 are "noisy" cables, i.e. badly made coaxial cables having a relatively loose centre conductor 18.
When such a cable is moved, centre conductor 18 moves relative to the outer conductor 19, creating an induced voltage signal. It has been found that this "noise" signal is correlatable with the vibration o* the cable; that is, if the cable is vibrated at a subsonic frequency, the "noise" signal includes a component at the same subsonic frequency. A large resistor is placed across the center and outside conductors 18, 19 of each of cables 8 so that induced voltage causes a current to flow through cable 8. A
coaxial cable is preferred because it produces a relatively reproducible electrical signal in response to physical movement of the cable, but alternatives, such as a twisted pair of wires running the length of the plates, could be used in place of a coaxial cable.
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The present inventor has recognized that when a humanbeing jumps or falls onto, walks on, or otherwise comes into relatively sharp and sudden contact with contact plates 6, vibrations are created. These vibrations tend to have a fairly broad-band frequency spectrum. However, the present inventor has analyzed this frequency spectrum, and has found that it invariably includes major frequency nodes in the sùbsonic frequency range, i.e. frequencies below about 15 Hz.
In particular, a human being dropping onto the contact plates 6 from a height of about l meter creates one frequency node at about 10-ll Hz and another at about 3 Hz. The lO Hz node is believed to be caused by the human being bouncing upon impact.
The frequency of this collision or "bounce" node frequency is dependent upon the speed of impact of the human being, which in turn is dependent upon the height of the passenger platform relative to the surface of the contact plates. The 3 Hz node is believed to reflect the inhomogeneous nature of a human being -upon impact, compressible flesh vibrates relative to incompressible bones, at a frequency of about 3 Hz. It might be therefore said that human beings have a natural frequency of 3 Hz, since human flesh vibrates at such frequency in response to a sudden impact. Thus it has been found that collisions between a human being and contact plates cause vibrations which include a collision frequency node dependant upon the height of the passenger platform and a natural frequency node of about 3 Hz.
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In addition, when a human being walks or runs on contact plates 6, an additional subsonic frequency node is created. In the case of walking, the node tends to be around 1-2 Hz, the walking frequency of a human being, because as a human being walks on the plates, a periodic thrust having a horizontal component is imparted to the contact plates. Obviously, typically running frequencies for human beings will be somewhat higher than walking frequencies.
In order to ensure that all of the above subsonic signature frequency nodes are picked up by (i.e. imparted to) vibration pick-up means 2, contact plates 6 must be capable of readily vibrating at such subsonic frequencies. In other words, the natural frequency of vibration pick-up means 2 itself must be in the subsonic range, so that resonance will occur when vibration pick-up means is subjected to driving forces in the subsonic range. This is achieved by mounting contact plates 6 on resilient support means 14, so that contacting plates are free to move a considerable distance back and forth in response to subsonic driving frequencies. It will be appreciated that considerable "displacement" of contact plates 6 is needed in order for the subsonic vibrations of interest to be imparted there, because if contact plates 6 were solidly mounted, the subsonic vibrations of interest would be mechanically attenuated, since the natural frequency of a solidly mounted plate would be well into the sonic range. In the preferred embodiment, ,, ' '~ ~
resilient blocks 16 are blocks of closed eell urethane foam about 1 3/8 inch in thickness, having a density enabling them to be compressible to about 3/8 inch. Thus the "displacement" of the resiliently mounted contact plates 6 is about 1 inch~ However, it will be appreciated that other types of resilient supports, such as springs with a suitable k constant, could be used instead of urethane blocks.
Referring now to Figure 3, signal analyzing means 3 of one embodiment of the present invention comprises filtering means 25, measuring means 26, and alarm generating means 35. Filtering means 25 amplifies the portion of the cable signal within the subsonic frequency range of interest and attenuates the portions of the cable signal outside such frequency range. Filtering means 25 comprises preamplifier 27, band pass filter 28, and line preamplifier 29. Preamplifier 27 is an operational amplifier whieh amplifies the cable signal by a factor of about 5 to 1, and whieh has a cut-off frequency of about 20 Hz. Band pass filter 28 attenuates those frequency components of the cable signal 21 which are outside the subsonic frequencies of interest, by a faetor of about 100 to 1. Line preamplifier 29 amplifies the output of band pass filter by a factor of about 40 to 1, and has a eut-off frequency of about 12 Hz.
7~L~S~3 Figure 4 illustrates the frequency response of filtering means 25, which acts like a low pass filter having a cut-off at about 7 or 8 Hz. It should be noted that filtering means 25 does not completely filter out the 10 Hz human collision frequency node, because this collision frequency node tends to be of considerably higher amplitude than the human natural frequency node at 3 Hz.
Referring again to Figure 3, filtered and amplified signal 30 is fed into measuring means 26, comprising Schmitt trigger 32 and pulse length separator 33. Schmitt trigger 32 reacts to the value of the slope of the leading edge of incoming signal 30. If the slope is above a pre-selected value, Schmitt trigger 32 triggers, i.e. it changes state from high to low value, or vice versa. Pulse length separator 33 measures the length of time that the Schmitt trigger 32 remains latched in a particular state. If the latching time is greater than a pre-determined time as discussed in detail below, an alarm signal 34 is generated by pulse length separàtor 33.
It should be noted that noisy coaxial cable 8 picks up not only the subsonic vibration signals of interest, but also various background signals in other frequency ranges, including a 60 Hz spike caused by nearby 60 cycle electrical equipment, a signal on the order of 600 Hz produced by the wheels of the ...... : .' -, . ~ , :
approaching -train interacting with the rails, and higher frequency audible signals caused by passengers talking. Thus, as noted above it is necessary to filter the cable signal by filtering means 25, with a view to removing signals outside the subsonic range of interest. However, band pass and cut-off filters are not perfect. Signals outside the cut-off frequency which are several orders of magnitude greater in amplitude than the signals of interest will be attenuated, but not completely eliminated. Therefore, filtered signal 30 will from time to time include high frequency spikes which trigger Schmitt trigger 32.
To avoid false alarms caused by such high frequency spikes, the output of Schmitt trigger 32 is monitored by pulse length separator 33. High frequency spikes are of very short duration, so they cause the Schmitt trigger 32 to stay latched for only a short period of time, whereas a true subsonic signal causes Schmitt trigger 32 to stay latched for a relatively long period of time. Therefore, pulse length separator 33 is designed to generate an alarm signal only i~ Schmitt trigger 32 stays latched for more than a pre-determined latching time. The latching time period is controlled by an adjustable resistor, which is field adjustable to suit the particular application. If a fast response time is necessary, as is the case with the emergency stop system of the preferred embodiment, the latching time should be made as short as possible without causing too many false alarms. It has been found that a latching time of about 1/4 second is a good compromise for many applications.
,. ....................... .. ..... . .
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Alarm signal 34 is then fed into alarm generating means 35, which may include a timer and relay drive 36, various relays 37 and an sonalert driver circuit 38. Timer and relay drive 36 includes a timer which latches for a relatively long set time of approximately 2 seconds, in response to the relatively short alarm signal 34, in order to produce an appropriate signal for driving relays 37.
The present invention may also include monitoring equipment, such as chart recorder for measuring the signals produced at various points in the circuitry. As shown in Figure 3, filtered and amplified signal 30 is split up and fed into chart recorder 40, which is used to calibrate the sensitivity of the system.
Figure 5 is a schematic diagram of the presently preferred embodiment of signal analyzing means 3. Vibration of cable 8 produces an electrical signal across resistor 22 which typically includes the subsonic frequency nodes of interest as well as higher frequency components including very high amplitude transients. The output of cable 8 is applied to operational amplifier 41, which converts the high impedence signal from cable 8 to a low impedence output signal. Operational amplifier 41 acts as an amplifier and filter in that it amplifies the subsonic frequency nodes of interest by a factor of up to 10 to 1 and .. ...
- : . ~- : .- :
~ ,, : .- - .
- ~:.. .. : -.. . , ., . .,: ,. , 3~
attenuates higher frequency signals by a factor of up to 10 to 1.
Potentiometer 42 controls the gain of operational amplifier 41.
The output of operational amplifier 41 is supplied both to broken sensor circuit 60, explained in more detail below, and to low pass filter 43. Low pass filter 43 is a fourth order filter comprising four operational amplifiers 44, 45, 46 and 47, which are connected in series to give an attenuation factor of 24 db per octave. The cut off frequency of low pass filter 43 is about 8 Hz. Low pass filter 43 filters out all high frequency components of the signal, except for very high amplitude transients. The output of low pass filter 43 is applied to diode 48, which removes the positive voltage component of the signal.
Diode 48 is connected to transient suppressor circuit 49, comprising adjustable resistor 50 and capacitor 51, which removes the high amplitude, high frequency transients from the signal, because such transients are not of sufficient duration to discharge capacitor 51. The output of transient suppressor circuit 49, which now consists solely of the subsonic frequency nodes of interest, is supplied to visual display circuit 52 and to monostable circuit 53.
Monostable circuit 53 comprises a 555 monostable multivibrator 54, which triggers when the input signal drops below a given threshold voltage. Alarm duration circuit 55 adjusts the duration of the output of monostable multivibrator 54 . ;. ,: ::.. : : . i ~
~'~7~
from 1 to 10 seconds. The output of monostable multivibrator 54 drives LED 56 and turns off a transistor 57, which is normally in an "on" state. Transistor 57 opens relay 58, which in turn drives alarm circuit 59. Transistor 57 is kept in a normally ~on" state, so that an alarm condition will be generated in the event of a power failure.
Broken sensor circuit 60 creates an alarm condition in the event that cable 8 is cut or otherwise broken. Broken sensor circuit 60 comprises comparator 61, one input of which is kept at a constant reference voltage by voltage divider 62. The other input of comparator 61 is connected to the output of operational amplifier 41. When cable 8 is cut, the amplitude of the output of operational amplifier 41 becomes greater than the reference voltage, causing comparator 61 to prcduce an output signal. This output signal drives LED 63 and turns off transistor 57, causing relay 58 to open.
In operation, when a passenger comes into contact with one or more of vibratory contact plates 6, such contact will create vibrations over a broad-band frequency spectrum. Included in that spectrum are certain subsonic frequency nodes characteristic of human intruders, as discussed above. These subsonic frequency nodes act to "drive" the vibratory contact plates. Because the natural frequency of the contact plates is close to the driving frequency, the plates will resonant at such ..
: ' ' ' . ' - ~ ~ " ' `:
~3 driving frequency. Since the coaxial cable is mechanically coupled to contact plates 6, the resonance of the contact plates will cause coaxial cable 8 to vibrate in unison. As the inner conductor of cable 8 moves relative to the outer conductor, and electrical signal having frequency nodes in the subsonic range, correlatable with the subsonic vibrations of the contact plates, is created. This electrical signal is first filtered by signal analyzing means 3 to remove, to the extent possible, all components of the cable signal outside a subsonic frequency range of interest. The amplitude of the filtered signal is then measured. If a true subsonic signal of sufficient amplitude is detected, signal analyzing means 3 will generate an output alarm signal indicative of an alarm condition. Otherwise, no alarm signal will be generated.
The response time of the subject intrusion detection apparatus is relatively fast, about 1/4 second. Accordinglyj when used as an emergency train stop system, use of the present invention has resulted in the capability of stopping a driver-less electric light rapid transit train, approaching a passenger platform at approximately 30 miles per hour in braking mode, within 40 meters. This would mean, in the case of a passenger platform of 80 meters in length, that if an intrusion into the train path occurs in the middle portion of the platform just as -the front of the train reaches the front of the platform, it would be possible to stop a train before it reaches the point -. : - . ........ . .
: . .. . .
, . ", .
P~3~3 of intrusion. It will be appreciated, however, that the s-topping distance will vary with the effectiveness of the train's braking system and other external factors.
The present invention is not limited to detecting only human intruders, but rather it is designed to detect other objects which are large enough to damage a train. The apparatus of the present invention can detect the presence of dogs and other relatively large animals on the tracks because a collision between such animals and contact plates 6 produces both natural frequency nodes and collision frequency nodes which are in the subsonic frequency range monitored by signal analy~ing means 3.
The presence on train tracks of various types of heavy inanimate objects, such as boulders, can also be detected by the subject -apparatus, even though these objects do not exhibit the phenomenom of body components vibrating relative to each other upon sudden impact, because such objects still exhibit a subsonic collision or bounce frequency dependant upon the height of the fall. Thus the apparatus of the present inven-tion could be adapted for installation on sections of tracks extending under overpasses several meters high, by tuning the apparatus to monitor a collision frequency correlatable with the height of the overpass.
.
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Furthermore, the intruder detection apparatus of the presen-t invention is not limited to emergency train s-top systems.
It could be used as an interface between the public and a variety of other off-limits areas which are not adapted to be secured by a physical barrier. For example, a series of contact plates could be laid down around the periphery of a docked ship and on the gang-plank, in such a way that unauthorized persons attempting to enter the ship would necessarily have to walk on the contact plates.
It will also be apparent that the embodiments of the invention disclosed herein could be computerized by digitizing the output of the coaxial cable or the output of the signal filtering means. This digitized signal could then be processed by microprocessor based signal processing means. For example, reference values for various parameters could be stored in the ROM (Read Only Memory) of a microcomputer, and then the microcomputer could be programmed to compare the current values of such parameter against the reference values thereof.
Accordingly, while the present invention has been described and illustrated with respect to the preferred embodiments, those skilled in the art will appreciate that numerous variations of the preferred embodiments may be made without departing from the scope of the invention, which is defined in the appended claims.
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Claims (20)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. Apparatus for detecting intruders in an off-limits area and for generating an alarm signal in response thereto, comprising:
(a) vibration pick-up means located in the off-limits area for picking up vibrations caused by an intruder coming into contact therewith and for generating an electrical signal correlatable with such vibrations, the vibration pick-up means comprising a flexibly mounted contact surface which vibrates in response to being contacted by an intruder, and conversion means coupled to the contact surface for converting mechanical vibrations of the contact surface into an electrical signal, and (b) signal analyzing means for analyzing the electrical signal generated by the vibration pick-up means, including selecting means for selecting a subsonic portion of the signal within a predetermined subsonic frequency range, and measuring means for making a measurement of at least one pre-selected parameter of the subsonic portion of the signal and for generating an alarm signal depending upon the outcome of said measurement.
(a) vibration pick-up means located in the off-limits area for picking up vibrations caused by an intruder coming into contact therewith and for generating an electrical signal correlatable with such vibrations, the vibration pick-up means comprising a flexibly mounted contact surface which vibrates in response to being contacted by an intruder, and conversion means coupled to the contact surface for converting mechanical vibrations of the contact surface into an electrical signal, and (b) signal analyzing means for analyzing the electrical signal generated by the vibration pick-up means, including selecting means for selecting a subsonic portion of the signal within a predetermined subsonic frequency range, and measuring means for making a measurement of at least one pre-selected parameter of the subsonic portion of the signal and for generating an alarm signal depending upon the outcome of said measurement.
2. The apparatus as defined in claim 1, wherein the contact surface comprises at least one contact plate.
3. Apparatus as defined in Claim 2, wherein the contact plate is supported on resilient support means.
4. Apparatus as defined in claim 3, wherein the resiliency of the resilient support means is selected such that the contact plate has a natural frequency within the predetermined subsonic frequency range.
5. Apparatus as defined in claim 1, wherein the predetermined subsonic frequency range of the selecting means includes a subsonic natural frequency node caused by components of the intruder's body vibrating relative to each other upon sudden impact with the vibration pick-up means.
6. Apparatus as defined in claim 1, wherein the predetermined subsonic frequency range of the selecting means includes a subsonic collision frequency node resulting from the intruder's body bouncing on impact with the vibration pick-up means.
7. Apparatus as defined in claim 1, wherein the pre-selected parameter is the amplitude of the subsonic portion of the signal.
8. Apparatus as defined in claim 2, wherein the contact surface comprises at least one row of horizontally disposed contact plates each independently supported on resilient support means.
9. Apparatus as defined in claim 1, wherein the vibration pick-up means has a natural frequency in the subsonic range, so that the vibratory pick-up means resonates in response to driving forces in the subsonic range.
10. Apparatus as defined in claim 8, wherein the resilient support means includes resilient blocks each adapted to support a corner of the contact plates.
11. Apparatus as defined in claim 1, wherein the conversion means comprises a noisy coaxial cable mechanically coupled to the contact surface.
12. Apparatus as defined in claim 8, wherein the conversion means comprises a noisy coaxial cable mechanically coupled to each of the rows of contact plates along substantially the entire length thereof.
13. Apparatus as defined in claim 1, wherein the measuring means includes circuit means for measuring the amplitude of the said subsonic portion of the signal.
14. Apparatus as defined in claim 1, wherein the selecting means incudes a low pass filter for attenuating components of the signal above the predetermined subsonic frequency range.
15. Apparatus as defined in claim 14, wherein the cut-off frequency of the low pass filter is about 8 Hz.
16. Apparatus as defined in claim 14, wherein the measuring means includes circuit means for receiving the output of the selecting means and for measuring the amplitude thereof.
17. Apparatus as defined in claim 16, wherein the measuring means includes a Schmitt trigger circuit and a circuit for measuring the time during which the Schmitt trigger circuit remains latched.
18. Apparatus as defined in claim 1, wherein the predetermined frequency range is selected to include both a subsonic natural frequency node resulting from components of an intruder's body vibrating relative to each other and a subsonic collision frequency node resulting from the intruder's body bouncing on impact.
19. Apparatus for detecting intrusions of an off-limits area by selected intruder and for generating an alarm signal in response thereto, comprising:
(a) a contact surface for contacting an intruder and for vibrating in response thereto;
(b) conversion means coupled to the contact surface for converting mechanical vibrations of the contact surface into an electrical input signal;
(c) selection means for receiving the input signal and for generating a derivative signal by amplifying components of the input signal within a subsonic frequency range of interest and by attenuating components of the input signal outside said frequency range of interest; and (d) processing means for processing the derivative signal so as to identify selected intrusions, including measuring means for making a measurement of current values of at least one pre-selected parameter of the derivative signal and for generating an output signal dependent upon such measurement.
(a) a contact surface for contacting an intruder and for vibrating in response thereto;
(b) conversion means coupled to the contact surface for converting mechanical vibrations of the contact surface into an electrical input signal;
(c) selection means for receiving the input signal and for generating a derivative signal by amplifying components of the input signal within a subsonic frequency range of interest and by attenuating components of the input signal outside said frequency range of interest; and (d) processing means for processing the derivative signal so as to identify selected intrusions, including measuring means for making a measurement of current values of at least one pre-selected parameter of the derivative signal and for generating an output signal dependent upon such measurement.
20. Apparatus for automatically generating a signal capable of activating the braking system on an approaching train in response to intrusions into the path of the train by human beings, comprising;
(a) at least one linear series of horizontally disposed contact plates mounted in the path of the train below the top surface of the rails on resilient support means, for contacting human beings coming into the path of the train and for vibrating in response thereto;
(b) a noisy coaxial cable mechanically coupled to the linear series of contact plates along sustantially the entire length thereof so as to vibrate in response to the vibrating of the contact plates with the result that an electrical input signal correlatable with the plate vibrations is generated;
(c) signal component selection means for receiving the input signal and for generating a derivative signal by amplifying components of the signal within a pre-selected subsonic frequency range by attneuating to components of the input signal outside such range.
(d) signal processing means for processing the derivative signal so as to differentiate between intrusions by human beings and false alarms, including measuring means for making a measurement of current values of at least one pre-selected parameter of the derivative signal and for preparing such values with reference values for such parameters and for generating an output signal dependant upon such comparison; and (e) alarm signal generating means responsive to the output signal transmitting an alarm signal for interfacing with the braking system of the approaching train.
(a) at least one linear series of horizontally disposed contact plates mounted in the path of the train below the top surface of the rails on resilient support means, for contacting human beings coming into the path of the train and for vibrating in response thereto;
(b) a noisy coaxial cable mechanically coupled to the linear series of contact plates along sustantially the entire length thereof so as to vibrate in response to the vibrating of the contact plates with the result that an electrical input signal correlatable with the plate vibrations is generated;
(c) signal component selection means for receiving the input signal and for generating a derivative signal by amplifying components of the signal within a pre-selected subsonic frequency range by attneuating to components of the input signal outside such range.
(d) signal processing means for processing the derivative signal so as to differentiate between intrusions by human beings and false alarms, including measuring means for making a measurement of current values of at least one pre-selected parameter of the derivative signal and for preparing such values with reference values for such parameters and for generating an output signal dependant upon such comparison; and (e) alarm signal generating means responsive to the output signal transmitting an alarm signal for interfacing with the braking system of the approaching train.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000543720A CA1273428A (en) | 1987-08-04 | 1987-08-04 | Intrusion detection apparatus |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000543720A CA1273428A (en) | 1987-08-04 | 1987-08-04 | Intrusion detection apparatus |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1273428A true CA1273428A (en) | 1990-08-28 |
Family
ID=4136205
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000543720A Expired - Lifetime CA1273428A (en) | 1987-08-04 | 1987-08-04 | Intrusion detection apparatus |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1273428A (en) |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5194848A (en) * | 1991-09-09 | 1993-03-16 | Hitek-Protek Systems Inc. | Intrusion detection apparatus having multiple channel signal processing |
| US5268672A (en) * | 1991-09-09 | 1993-12-07 | Hitek-Protek Systems Incorporated | Intrusion detection system incorporating deflection-sensitive coaxial cable mounted on deflectable barrier |
| WO2017171539A1 (en) * | 2016-03-31 | 2017-10-05 | Azti Technology Sdn. Bhd | A system to detect human intrusion |
| WO2023014214A1 (en) * | 2021-08-05 | 2023-02-09 | Azti Technology Sdn Bhd | A railway obstacle warning system |
-
1987
- 1987-08-04 CA CA000543720A patent/CA1273428A/en not_active Expired - Lifetime
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5194848A (en) * | 1991-09-09 | 1993-03-16 | Hitek-Protek Systems Inc. | Intrusion detection apparatus having multiple channel signal processing |
| US5268672A (en) * | 1991-09-09 | 1993-12-07 | Hitek-Protek Systems Incorporated | Intrusion detection system incorporating deflection-sensitive coaxial cable mounted on deflectable barrier |
| WO2017171539A1 (en) * | 2016-03-31 | 2017-10-05 | Azti Technology Sdn. Bhd | A system to detect human intrusion |
| AU2016399957B2 (en) * | 2016-03-31 | 2021-12-02 | Azti Technology Sdn. Bhd | A system to detect human intrusion |
| WO2023014214A1 (en) * | 2021-08-05 | 2023-02-09 | Azti Technology Sdn Bhd | A railway obstacle warning system |
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