Communications: electrical – Condition responsive indicating system – Specific condition
Reexamination Certificate
1999-07-01
2001-08-07
Tong, Nina (Department: 2632)
Communications: electrical
Condition responsive indicating system
Specific condition
C340S545300, C340S567000
Reexamination Certificate
active
06271754
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to electrical intrusion detection devices, and in particular to railway signal and hazard detection systems.
BACKGROUND OF THE INVENTION
Railway hazard detection systems have been employed for many years, to detect track discontinuities, such as breaks or severe misalignments. Prior systems commonly loop an electrical circuit through a portion of track and detect a discontinuity in the track by a corresponding break in the circuit. However, these detection systems are usually inadequate to detect certain hazards occurring on a railway, such as landslides and falling boulders that impinge on but do not break or misalign the tracks. Accordingly, additional systems are usually employed to detect these hazards at locations at which they are likely to occur.
One manner of landslide detection involves stringing a number of current-carrying wires up-hill from the railway. When a falling rock, or similar object, breaks a wire, the flow of current through the wire stops and an alarm circuit is tripped. This type of detection system has several drawbacks. First, it may be expensive and time consuming to install the various wires, especially in locations with rugged terrain. Second, depending upon the relative spacing of the wires, some objects may be able to pass through, over, or under the wires and thereby evade detection. Third, after a break occurs, extensive repairs may be necessary to restore the integrity of the wire network.
Another prior landslide detection system relies on changes to an electromagnetic field established between two graded, “leaky” cables to detect an intrusion. As shown in
FIG. 1
, two coaxial cables, namely, a transmit cable
2
and a receive cable
4
, are deployed at a constant distance from each other along an area of interest. The cables are specially manufactured so that their shields have a plurality of slots
8
along their lengths, to allow a small amount of signal energy to couple from the transmit cable
2
to the receive cable
4
. To compensate for signals loses along the cables, the separations between the slots are decreased and sizes of the slot openings are increased with distance from the transmitter and receiver. For intrusion detection, the electromagnetic field associated with the cables must be essentially uniform along the cable length. Accordingly, the relative sizes and positions of the slots are critical. Further, terminators
6
having an impedance that is matched to the characteristic impedance of the cables are attached to the far end of each cable, to minimize signal reflections and standing waves that may produce false readings.
Under steady state, i.e., non-intrusive, conditions, the electromagnetic field
7
is static and the received signal has a constant magnitude and phase. When an object comes near either cable, or between the cables, the electromagnetic field is perturbed, causing a change in the magnitude and/or phase of the received signal.
Unfortunately, the use of graded, leaky coaxial cable in such systems has some significant drawbacks. First, because the size and spacing of the slots can only be adjusted by a finite amount before affecting the characteristic impedance of the cables, there is a fundamental limitation on run length. Second, the cables must be special-ordered and are expensive to manufacture. Third, great care must be taken during installation to properly orient the cables, so that an essentially constant field may be achieved. Lastly, repairs to damaged cable present special problems. While short sections of graded cable may be repaired using a standard patch kit, the replacement of a longer section is difficult because the new cable section must have slots that are properly spaced and sized, to avoid a significant impact on performance. Accordingly, a relatively large inventory of graded cable sections must be maintained.
SUMMARY OF THE INVENTION
An intrusion detection system includes a transmitter and a receiver that are connected to opposite ends of a cable assembly. In a first embodiment, the cable assembly is comprised of a pair of transmit and receive cables that are separated at a constant distance from each other and couple along their lengths. The transmitter is connected to the transmit cable at one end of the assembly and transmits a continuous wave radio frequency signal (“CW RF”) into the cable. The signal is emitted from the transmit cable with increasing attenuation along the cable length as the distance from the transmitter increases. The receiver is connected to the receive cable at the opposite end of the assembly, and the attenuated transmitted signal is detected with increasing sensitivity along the receive cable length as distance from the receiver decreases. The increase in the detection sensitivity along the length of the receive cable compensates for the increase in the attenuation of the transmitted signal, and an electromagnetic field produced between the cables is of essentially constant strength along the length of the assembly. An object intruding between, or proximate to, the coupled cables perturbs the electromagnetic field and causes a shift in the magnitude and/or phase of the received signal. When the receiver detects a relatively large, abrupt shift in the phase or magnitude of the received signal, the receiver sets off an alarm to indicate an intrusion.
In a second embodiment, the cable assembly is comprised of a single detection cable with the transmitter and receiver connected to opposite ends. The transmitter transmits a CW RF signal into the transmit end of the detection cable, which produces an electromagnetic field around the cable. An object intruding into the electromagnetic field causes a change in the effective dielectric constant of the cable which, in turn, causes a shift in the phase of the signal received by the receiver. This shift may be positive or negative, depending on whether the object has entered or departed the field. Therefore, this cable configuration can differentiate between landslides and washouts, for example.
REFERENCES:
patent: 401472 (1889-04-01), Taylor
patent: 3477019 (1969-11-01), Hartmann
patent: 3696243 (1972-10-01), Risely
patent: 3740549 (1973-06-01), Thorne-Booth
patent: 3967262 (1976-06-01), Reich et al.
patent: 4032916 (1977-06-01), Galvin et al.
patent: 4091367 (1978-05-01), Harman
patent: 4155083 (1979-05-01), Slaats et al.
patent: 4327358 (1982-04-01), Karas
patent: 4401980 (1983-08-01), Rittenbach et al.
patent: 4562428 (1985-12-01), Harman et al.
patent: 4571578 (1986-02-01), Karas
patent: 4886226 (1989-12-01), Frielinghaus
patent: 4987394 (1991-01-01), Harman et al.
patent: 5440291 (1995-08-01), Foster, Jr. et al.
patent: 5521600 (1996-05-01), McEwan
patent: 5529267 (1996-06-01), Giras et al.
patent: 5581256 (1996-12-01), McEwan
patent: 5680054 (1997-10-01), Gauthier
patent: 5743495 (1998-04-01), Welles, II et al.
patent: 5769364 (1998-06-01), Cipollone
Cesari and McKenna LLP
Microlynx Systems, Ltd.
Tong Nina
LandOfFree
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