U.S. patent application number 09/282273 was filed with the patent office on 2001-11-29 for fiber optic rail monitoring apparatus and method.
Invention is credited to CHAN, ANDREW K., OLSON, LESLIE E., ROOP, STEPHEN S., SU, CHIN.
Application Number | 20010045495 09/282273 |
Document ID | / |
Family ID | 23080769 |
Filed Date | 2001-11-29 |
United States Patent
Application |
20010045495 |
Kind Code |
A1 |
OLSON, LESLIE E. ; et
al. |
November 29, 2001 |
FIBER OPTIC RAIL MONITORING APPARATUS AND METHOD
Abstract
Systems and methods for are described for the detection of
breaks in railroad track rails as well as other events. A plurality
of fiber optic monitoring assemblies are located proximate a
section of railroad tracks. The monitoring assemblies are capable
of detecting and recognizing a rail break event. In an alternative
embodiment, systems and methods are described for detection of flat
spots on rail car wheels.
Inventors: |
OLSON, LESLIE E.; (BRYAN,
TX) ; ROOP, STEPHEN S.; (COLLEGE STATION, TX)
; SU, CHIN; (COLLEGE STATION, TX) ; CHAN, ANDREW
K.; (COLLEGE STATION, TX) |
Correspondence
Address: |
SHAWN HUNTER
ONE RIVERWAY, SUITE 1100
HOUSTON
TX
77056
US
|
Family ID: |
23080769 |
Appl. No.: |
09/282273 |
Filed: |
March 31, 1999 |
Current U.S.
Class: |
246/121 |
Current CPC
Class: |
B61L 23/044
20130101 |
Class at
Publication: |
246/121 |
International
Class: |
B61L 023/04 |
Claims
What is claimed is:
1. A method of detecting a break event in a rail segment
comprising: a) propagating energy from the break event to disturb a
sensing fiber; b) generating a signal in response to the
disturbance of the sensing fiber, the signal being indicative of
the break event.
2. The method of claim 1 further comprising the operation of
detecting the break event disturbance by processing the signal.
3. The method of claim 2 wherein the signal processing comprises
wavelet analysis.
4. The method of claim 3 wherein a template signal is created
through the wavelet analysis.
5. The method of claim 4 further comprising the operation of
comparing the template signal to a stored signal representative of
a rail break to determine whether a rail break event is present in
the template signal.
6. A method of detecting an event of interest associated with a
rail segment comprising: a) disposing a monitoring apparatus having
a particular length alongside and proximate a portion of the rail
segment, the monitoring apparatus capable of determining the
approximate location of an energy signature from an event of
interest along the length of the monitoring apparatus; and b)
receiving at the monitoring apparatus an energy signature
corresponding to an event of interest and detecting the energy
signature.
7. The method of claim 6 further comprising the operation of
generating an analog signal representative of the energy
signature.
8. The method of claim 7 further comprising the operation of
examining the analog signal to determine whether an event of
interest is present in the energy signature.
9. The method of claim 8 wherein examination of the analog signal
comprises the operations of deriving a template signal from the
analog signal and comparing the template signal to a stored signal
representative of the event of interest.
10. The method of claim 6 wherein a plurality of monitoring
apparatuses are disposed alongside adjoining portions of the rail
section so as to provide a substantially continuous monitoring
assembly.
11. A monitoring apparatus for detecting a disturbance associated
with a rail segment, the apparatus comprising an intrusion
detection device disposed alongside a rail section, the intrusion
detection device being operable to detect energy released from an
event of interest associated with the rail segment.
12. The monitoring apparatus of claim 11 wherein the intrusion
detection device comprises a fiber optic sensing fiber.
13. The monitoring apparatus of claim 12 wherein the intrusion
detection device further comprises a laser for directing a beam of
laser light through the sensing fiber.
14. The monitoring apparatus of claim 12 wherein the intrusion
detection device further comprises a signal generator for
generating a signal indicative of a disturbance of the sensing
fiber.
15. The monitoring apparatus of claim 14 wherein the intrusion
detection device further comprises a comparator for comparing the
generated signal to a prestored signal representative of the event
of interest.
16. The monitoring apparatus of claim 15 further comprising a
storage medium to contain a prestored signal representative of an
event of interest.
17. The monitoring apparatus of claim 15 further comprising a
signal analyzer to process the generated signal to create a
template signal for comparison to the prestored signal.
18. The monitoring apparatus of claim 14 further comprising an
analog to digital converter to convert the generated signal to a
digital signal.
19. The monitoring apparatus of claim 14 further comprising a
buffer for periodic storage of the generated signal.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] Not Applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] Not Applicable.
BACKGROUND OF THE INVENTION
[0003] 1. Field of the Invention
[0004] The present invention relates primarily to devices and
methods used for the detection of breakages and other failures in
railroad trackage. In other aspects, devices and methods are
described for the detection of deformations in railroad car
wheels.
[0005] 2. Description of the Related Art
[0006] Railroad tracks are made up of a pair of parallel, metal
rails and a plurality of cross ties which extend between the two.
If one of the metal rails breaks or ruptures, the track is unsafe
since rail traffic encountering the break can be derailed. The
energy released during the break of a metal rail is typically very
great since the break usually occurs when the rail is snapped under
very significant amounts of tension. A break in a rail during
winter months, when the metal of the rails tends to shrink, can
leave a separation between the two ends of the broken rail of up to
several yards. As a result, it is of critical importance to be able
to detect a rail break as soon as possible, so that rail traffic
can be stopped or diverted and the break repaired.
[0007] Railroads use various methods to try to detect broken rail
segments in their track system. The most basic and
manpower-intensive method is physical inspection of the track.
Because of the sheer length and number of tracks in existence
today, however, this method is simply impractical.
[0008] Electrical circuitry systems are known that employ current
impressed on a track segment to detect faults in the segment. An
example of this type of system is described in U.S. Pat. No.
4,117,463 entitled "Circuit Fault Detection Apparatus for Railroad
Track Circuit Redundant Connections." Operation of this type of
electrical monitoring system is accomplished by applying current
into the wiring to form a complete circuit. The circuit is
typically monitored by a wayside detector. A fault along the track
segment, such as a break in the metal rail, causes an interruption
of the circuit that, in turn, activates an appropriate alarm. This
type of electrical monitoring system is also used for the locating
of train traffic along a rail segment. However, if a break occurs
over a metal tie plate, the electric circuit may be maintained and
a false indication of continuous integrity is received by the
monitoring equipment. A false indication of integrity will also be
provided if the rail fails to break completely, although a serious
compressive fracture may be present.
[0009] Ultrasonic detection devices are also known for inspecting
rail welds in a track. A device of this type is detailed in U.S.
Pat. No. 3,960,005 entitled "Ultrasonic Testing Device for
Inspecting Thermit Rail Welds." Unfortunately, these devices are
primarily used for detecting flaws in welds and rail rather than
actual breaks. Ultrasonic inspections attempt to locate rail
defects which will potentially propagate into actual rail breaks in
the future. As a result, real time information is not provided as
to actual breaks. Additionally, rail in northern climes may have
very small defects which are not detected by ultrasonic inspection
but, subject to significant additional stresses cause the rail to
break at unexpected locations and times.
[0010] In addition, ultrasonic inspection requires track occupancy.
Train operations cannot be conducted on the section of track which
is being inspected, and inspection of long segments of track can
prove very time consuming. Rail sections which are used more often,
or which carry a higher tonnage, require a higher frequency of
inspection. Since the rail section is very busy, it can be
extremely difficult to schedule such inspections without impacting
rail operations for the section.
[0011] Recent developments in alternative train locating systems,
such as those involving global positioning systems (GPS), may
reduce or eliminate the need for electrical train locating systems,
such as that described above. Unfortunately, these alternative
systems do not provide a means for detecting rail breaks or other
faults. Therefore, the widespread use of alternative train locating
systems may be constrained by the continued need to leave the
electrical system in place to monitor rail breakage.
[0012] Experimental work involving the use of fiber optics and
lasers for the detection of rail breaks has been conducted recently
at the University of Illinois at Urbana-Champaigne. In this
experimental work, an optic fiber was directly adhered to a section
of railroad rail and low coherence laser light was pulsed through
the fiber. The experimentation included the testing of different
types of glues for use as the bonding agent for adhering the fiber
to the section of rail. Due to the direct adherence of the fiber to
the rail, a break in the rail would also be expected to physically
sever the optic fiber. An optical time domain reflectometery (OTDR)
break detector, of the type used for detecting breaks in
telecommunications optic fibers, was employed to determine when the
fiber was severed.
[0013] A system of this type has many drawbacks. Perhaps most
important is the fact that a breakage of the rail causes a
severance of the fiber. In order for the system to become
operational again, the fiber would have to be replaced or spliced
and then rebonded to the repaired rail.
[0014] Further, the bonding agent can deteriorate over time
allowing the fiber to become loosened from the rail and,
thereafter, damaged by environmental hazards. Since optical fibers
are extremely thin and somewhat fragile, the damage could occur
easily. Even when bonded to the rail, the fiber is vulnerable to
damage from environmental hazards such as vandalism or tampering.
Also, repair work or replacement of sections of the rail will
necessitate breakage and replacement of the fiber.
[0015] Thus, a need exists for a workable alternative system and
method for monitoring. The present invention addresses the problems
inherent in the prior art and provides a system and method for
monitoring rail sections without requiring electrical
circuitry.
SUMMARY OF THE INVENTION
[0016] The present invention relates broadly to the use of fiber
optic technology as applied to railroad track and traffic
monitoring. In an exemplary described embodiment, fiber optic based
monitoring assemblies are used to detect localized disturbances
occurring along a section of track. Specifically, the monitoring
assemblies are capable of detecting breaks in a particular portion
of a rail section.
[0017] In preferred embodiments, the monitoring assemblies are
disposed in series proximate a section of rail or track. The
assemblies adjoin one another so as to monitor the continuous
length of the rail section. Each of the monitoring assemblies
includes fiber optic intrusion sensing apparatus having extended
linear sensing fibers. Each of the monitoring assemblies are
capable of determining the approximate location along the rail
segment wherein a break event has occurred.
[0018] Wavelet analysis is used by the monitoring assembly to
identify the disturbance caused by a rail break and to distinguish
that event from other potential disturbances. In the described
preferred embodiments, the monitoring assemblies also include a
storage media within which is recorded the fact and approximate
location of a rail break.
[0019] Another aspect of the invention is described in which the
fiber optic monitoring assemblies are used to detect other
identifiable disturbance or conditions. For example, the assemblies
could be used to detect the presence of rail cars having flat spots
on their wheels.
[0020] Thus, the present invention comprises a combination of
features and advantages which enable it to overcome various
problems of prior devices. The various characteristics described
above, as well as other features, will be readily apparent to those
skilled in the art upon reading the following detailed description
of the preferred embodiments of the invention, and by referring to
the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] For a more detailed description of the preferred embodiment
of the present invention, reference will now be made to the
accompanying drawings, wherein:
[0022] FIG. 1 is a sketch depicting exemplary rail break detection
apparatuses located alongside a section of track.
[0023] FIG. 2 is a schematic view showing the components of an
exemplary monitoring apparatus.
[0024] FIG. 3 is a schematic view of an exemplary external cavity
semiconductor laser as used in the monitoring assembly of FIG.
2.
[0025] FIGS. 4A-4D depict exemplary signals being processed and
analyzed in accordance with the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0026] Referring first to FIG. 1, an exemplary rail break detection
system, indicated generally at 10, is shown positioned alongside a
section 12 of railroad track. The track section 12 is composed of a
pair of sections of longitudinal metal rails 14, 16 that are
disposed in a parallel relation to one another. A plurality of
cross-ties 18 extend between the rails 14, 16. The track section 12
is shown containing a break 20 in one of the longitudinal metal
rails 14. It will be understood that the section 12 is but a small
portion of a larger rail system.
[0027] A plurality of monitoring assemblies 22, 24 are disposed
proximate to and substantially parallel to the track segment 12.
The assemblies 22, 24 are located adjacent one another so that
essentially the entire length of track segment 12 has a monitoring
assembly located parallel to it. Although only two such assemblies
are shown, it will be understood that as many assemblies are used
as needed to adequately cover the length of the track segment 12.
The monitoring assemblies 22, 24 each include a protective housing
26 and two optic sensing fibers 28, 30 that extend from the housing
26 in opposing directions.
[0028] The ends of the sensing fibers from adjoining monitoring
assemblies preferably overlap one another slightly to ensure
complete monitoring of the track segment 12.
[0029] The monitoring assemblies 22, 24, including their sensing
fibers, are preferably buried in the ground 32 adjacent the track
segment 12 approximately 2 feet below grade. The monitoring
assemblies 22, 24 can be placed much closer to the track segment 12
than 2 feet and still be operable. However, close placement to the
track segment 12 is not recommended currently since such close
placement would probably require the sensing fibers 28, 30 of the
monitoring assemblies to be buried within the ballast of the track
segment which would be costly to accomplish. Further, close
placement of a monitoring assembly to the track segment 12
increases the risk that the monitoring assembly might be physically
damaged during a rail break event or other event. Although the
length of the fibers 28, 30 is shown to be rather short in FIG. 1,
it should be understood that this is merely for the purpose of
depicting the invention. In practice, the fibers 28, 30 can
actually extend a significant linear distance (15-30 miles) outward
from the protective housings 26.
[0030] Construction and operation of the monitoring assemblies 22,
24 is understood with reference to FIG. 3 in which an exemplary
monitoring assembly 50 is shown. Although the monitoring assemblies
22 and 24 are shown each having two sensing fibers 28, 30, only a
single fiber is described with the exemplary monitoring assembly
50. The mechanics behind use of only a single fiber is described
for clarity and simplicity. It will be understood by those of skill
in the art that the use of two optical fibers could be supported by
doubling the number of relevant components within the monitoring
assembly.
[0031] The exemplary monitoring assembly 50 includes a fiber optic
intrusion sensing system that is capable of detecting the
approximate location of a disturbance or intrusion along a length
of sensing fiber 52. A high level schematic diagram of a currently
preferred embodiment is depicted in FIG. 2. An optical fiber 52
extends outwardly from the protective housing, which is shown
schematically at 56. The housing 56 encloses a laser and detector
58 that produces light pulses of relatively high coherence which
are injected into the optical fiber 52. The laser of 58, which will
be described in greater detail shortly, is preferably an external
cavity semiconductor laser that provides a coherent or nearly
coherent laser light.
[0032] The detector of 58 provides an analog electrical signal 60
to an analog-to-digital converter 62 that converts the analog
signal 60 into a digital signal 64. The analog signal 60 is
indicative of received backscattered laser light from the fiber 52,
and the specifics of the signal will be described in greater detail
shortly.
[0033] A rotary buffer 66 stores the digital signal 64. Presently,
the rotary buffer 66 preferably comprises 2 gigabytes of memory
storage. Stored signals 68 are selectively provided from the buffer
66 to a signal analyzer 70. The signal analyzer 70 is preferably a
signal processor similar to that described in U.S. Pat. No
5,262,958 entitled "Spline-Wavelet Signal Analyzers and Methods for
Processing Signals" issued to Chui et al. As will be described in
further detail shortly, the signal analyzer 70 decomposes an input
signal into splines and wavelet coefficients whereupon distinctive
events, such as material separation, may be identified. This
"wavelet analysis" permits signal analysis to be performed in
nearly real time.
[0034] The signal analyzer 70 provides a template signal 72 to a
comparator 74 which compares the template signal 72 to a reference
signal 76 which is maintained in a storage medium 80. The
comparator 74 preferably comprises a software algorithm that
determines whether the template signal 72 matches the reference
signal 76 within a predetermined degree of confidence. The
comparator 74 produces an output signal 82 depending upon the
result of the comparison between the two signals. For example, if
the template signal 72 matches the reference signal 76 within the
predetermined degree of confidence, a positive signal is generated.
If not, a negative signal is generated.
[0035] Generally, the laser 58 of the monitoring assembly 50
incorporates a photodetector that receives backscattered light from
a pulsed laser in the system. Disturbances of a sensing fiber
associated with the system will cause a change in the pattern of
light received at the photodetector, thus resulting in a detected
signal for the event causing the disturbance of the sensing fiber.
One particularly preferred type of fiber optic intrusion sensing
system is similar to that described in U.S. Pat. No. 5,511,086
entitled "Low Noise and Narrow Linewidth External Cavity
Semiconductor Laser for Coherent Frequency and Time Domain
Reflectometry" issued to Su and assigned to the assignee of the
present invention. That patent is incorporated herein by reference.
This system is characterized by a very narrow linewidth and low
noise external cavity semiconductor laser useful for sensitive
frequency and time domain reflectometry.
[0036] Referring now to FIG. 3, the structure and operation of an
exemplary laser 58 is described in further detail. A coherent
optical radiation or light beam 102 is generated by a light source
100, such as a semiconductor optical amplifier. Power supply 101
provides a pulsed current to the light source 100 so that a pulsed
laser light is produced. As will be discussed in further detail
shortly, it is preferred that the laser light beam be pulsed on a
very short periodic time schedule. It is particularly preferred
that the light beam 102 be produced at least once every millisecond
(ms). The wavelength of the light beam 102 may be set according to
application requirements, and may include wavelengths of 1.3 .mu.m,
1.5 .mu.m, and 0.8 .mu.m. The coherent light beam 102 from the
light source 100 passes through a collimating lens 104 which may be
a GRIN lens or SEL-FOC lens. The light beam 102 then passes through
a polarizing beam splitter (pbs) 106, and is then reflected by a
pair of mirrors 108 and 110 to pass through a Faraday rotator 112,
a half wave ({fraction (.lambda./)}2) plate 114, and another
polarizing beam splitter (pbs) 116. The polarizing beam splitter
106 rejects vertically polarized light from the light beam 102 and
allows horizontally polarized (or transverse electrical polarized)
light to be transmitted to the mirrors 108, 110.
[0037] The Faraday rotator 112 rotates the polarization of the
light beam 45.degree. in one direction, and the half wave plate 114
rotates the polarization of the beam by 45.degree. in the opposite
direction to return it to horizontal polarization. The resultant
polarization of the light beam after the combination of the Faraday
rotator 112 and the half wave plate 114 is horizontal. The second
polarizing beam splitter 116 further "filters" the light beam and
transmits only horizontally polarized portions of the light beam to
a solid or air gap etalon 118.
[0038] The etalon 118 may be a Virgo Optics Model ES254-010 having
a reflectivity of 97.5% and a thickness of 2 mm. As known in the
art, the parameters of the etalon 118 may be selected depending on
the dimension of the laser cavity. The etalon 118 performs multiple
tasks. First, the etalon 118 performs a strong selection for lasing
of only one single longitudinal-mode of the laser cavity. Second,
the etalon 118 reduces the laser's linewidth from approximately 100
kHz to approximately 15 kHz. Third, the etalon 118 reduces the
detected noise by filtering out spontaneous emissions. Due to the
etalon's reflectivity of 97.5%, the finesse of the etalon is 100 so
that the detected spontaneous emission noise is reduced by a factor
of 100. Finally, the etalon 118 reduces the detected spontaneous
emission noise from an external optical amplifier 120 used for
amplifying the power from the laser 58 and for implementing a
coherent time domain reflectometry technique.
[0039] The light beam exiting the etalon 118 proceeds to a beam
splitter 122 that divides the beam into two light beams progressing
on two different paths 124 and 126. Path 124 is the light output
path to the sensing fiber 52. The light beam traveling on the path
126 is reflected by a grating 128 to progress along path 130. The
grating 128 further performs, along with the etalon 118, the
function of selecting one single longitudinal mode of the laser for
lasing. The reflected light traveling along path 130 passes through
a lens 132 and returns to the back facet of the optical amplifier
100, becomes amplified by the amplifier 100, and leaves the front
facet of the diode amplifier 100 down the path of light beam 102
again. As the optical amplifier 100 continues to provide gain, the
horizontally polarized portion of the traveling light beam 102
becomes increasingly stronger, and the vertically polarized portion
essentially disappears.
[0040] The light beam traveling on the path 124 is used for
reflectometry measurements. The output light beam proceeds to a
second Faraday rotator 134 and then to an optical plate or half
wave plate 136 where a fraction of the light 138, hereinafter
referred to as the reference light P.sub.ref is reflected back
toward the Faraday rotator 134 from the optical plate 136. The
remaining light 140 is transmitted by the optical plate 136 through
a lens 142 to an optical amplifier 120. The optical amplifier 120
can be, and preferably is, a fiber optical amplifier or
semiconductor optical amplifier. The optical amplifier 120 is
biased at an appropriate DC level, for example, 100 mA for a
semiconductor optical amplifier. The amplified light is then
launched into the sensing fiber 52 for reflectometry measurements.
The half wave plate 136 is used if the gain in the amplifier 120 is
substantially the same for all axes. The side of the half wave
plate 136 facing the Faraday rotator 134 is coated with a
reflective coating to generate the reflected reference light
P.sub.ref 138.
[0041] The polarization of the reference light, P.sub.ref 138,
reflected by the optical plate 136 is rotated 90.degree. upon
exiting the Faraday rotator 134. The reflected reference light is
further deflected by the beam splitter 122 and the polarizing beam
splitter 116 into a detector 144. The detector 82 may be a New
Focus Model 1811. The detector 144 also functions as a signal
generator that generates the analog signal F(t) 60 indicative of
the received light.
[0042] The light traveling in the sensing fiber 52 is backscattered
by a disturbance or fault. The backscattered light from the sensing
fiber 52, herein referred to as the signal light, P.sub.sig,
follows the same path back through the beam splitter 122 and
polarizing beam splitter 116 as the reference light P.sub.ref 138
and is also detected by the detector 144 and provided as a portion
of the analog signal 60. The backscattered optical pulse signal
P.sub.sig is coherently mixed with the reference light P.sub.ref.
The time-delay of the return pulse signal P.sub.sig indicates the
distance to the reflection point.
[0043] The analog signal 60, or F(t), is converted by the analog to
digital converter 62 to the digital signal 64 wherein the digital
signal 64 is expressed as a function F(nh), where h is the pulsing
period of the analog signal 60 and n is the index of the sample
being considered. The digital signal 64 is then stored for a time
by the buffer 66 which then provides the digital signal, via signal
68, to the signal analyzer 70.
[0044] The signal analyzer 70 is used to conduct a time-domain
wavelet analysis of the signal 60 and create the template signal
72, which is then compared to the stored signal 76 from the storage
medium 80. Processing and analysis of the analog signal 60 to
create the template signal 72 allows for specific features of the
signal to be isolated and identified. Thus, comparison of the
template signal 72 to a prestored signal is more likely to reveal
the presence of an energy signature indicative of an event of
interest, such as a rail break.
[0045] The technique for creating the template signal 72 will be
described in general terms here. However, further description of
this type of analysis, and devices useful for performing it, is
found in U.S. Pat. No 5,262,958 entitled "Spline-Wavelet Signal
Analyzers and Methods for Processing Signals" issued to Chui et al.
That patent is incorporated herein by reference.
[0046] The signal analyzer 70 takes samples of the digital signal
68, the samples being F(0), F(2h), F(4h), F(6h) . . . , and
multiplies them by a series of weights W.sub.-4, W.sub.-3, W.sub.-2
. . . W.sub.0, W.sub.1, W.sub.2, W.sub.3, W.sub.4, in a moving
average operation to derive a plurality of zero-level scaling
function coefficients c.sup.0(n). The scaling function coefficients
c.sup.0(n) can be used to reconstruct the analog signal 60 as
F.sup.0(t) where F.sup.0(t) represents that the signal so derived
is an approximation to the original signal F(t).
[0047] A set of spline coefficients c.sup.0(n) is used as an input
to an A.sub.n memory (not shown) and a B.sub.n memory (not shown).
The A.sub.n memory contains constants a.sub.n which are used to
derive c.sup.-1(n) scaling function coefficients for the
approximated signal F.sup.0(t). The B.sub.n memory contains
constants b.sub.n which are used to derive d.sup.-1(n) wavelet
coefficients for the approximated signal F.sup.0(t). The
coefficients c.sup.-1(n) are used to derive a first-level
approximated function F.sup.-1(t). Similarly, the d.sup.-1(n) set
of coefficients is used to derive a first-level wavelet G.sup.-1(t)
as a compliment to the approximated signal.
[0048] In a similar manner, second-level wavelet coefficients
d.sup.-2(n) are derived from the first-level scaling function
coefficients c.sup.-1(n) and second-level coefficients c.sup.-2(n)
are also derived from the first-level spline coefficients
c.sup.-1(n). The derivation can be repeated for as many levels of
resolution as is deemed necessary.
[0049] Referring now to FIGS. 4A-4d, representative signals are
depicted of the type that might be produced by the present
invention. It should be understood that the signals depicted are
exemplary only and are depicted for the purpose of explaining the
functioning of the invention. As measured and processed, actual
signals may appear quite different from those depicted here.
[0050] FIG. 4A shows an exemplary analog signal 60 as produced by
the detector 144 of the laser 58. The signal 60 is shown as a
function F.sup.0(t) that has a particular intensity or signal
strength over time (t). The spikes 150, 152, 154, 156 in the signal
60 are indicative of laser pulsing. As shown, the intensity of the
signal decays after each spike 150, 152, 154, 156. It can also be
seen that the signal 60 is somewhat irregular due to the presence
of noise or minor disturbances of the sensing fiber 52. It will be
appreciated that the signal 60 depicts a laser that is pulsed
approximately every 0.75 ms. The effect of one minor disturbance
157 can be seen affecting the decay of a laser pulse-induced spike.
This disturbance might be caused by train or vehicular traffic or
some other source.
[0051] A discontinuity 158 in the signal 60 is due to a rail break
event. The event has occurred over a short period of time
(approximately 0.25 ms) and creates a significant increase in the
amplitude of the signal 60. As compared to the disturbance 157, the
discontinuity 158 results from a greater release of energy
occurring over a shorter period of time, thus accounting for its
increased height and shorter duration.
[0052] FIG. 4B illustrates the digital signal F(nh) 64, obtained by
processing the analog signal 60 via the analog-to-digital converter
62. It can be seen that the spikes 150, 152, 154 and 156 have been
converted to discrete-time signals 160, 162, 164 and 166. The
disturbance 157 and discontinuity 158 become discrete-time signals
167 and 168, respectively.
[0053] FIG. 4C depicts the template signal 72 that is achieved by
wavelet analysis performed by the signal analyzer 70. The template
signal 72 provides a series of recognizable wavelet coefficients
170, 172, 174, 176 which correspond to the discrete-time signals
160, 162, 164 and 166 of the digital signal 64. Wavelet signatures
178, 180 are also present for the discrete-time signals 167 and
168.
[0054] FIG. 4D depicts a stored signal 76 which represents the
wavelet signature of a rail break event 182. As can be seen, the
stored rail break signature 182 corresponds closely to the wavelet
signature 180 for the rail break event as derived from the analog
signal 60. As noted, the comparator 74 will compare signals 72 and
76 to determine whether there is a match for the stored signature
182 present in the template signal 72.
[0055] When a break 20 occurs, an energy signature 100 is released
into the surrounding earth 32, as depicted in FIG. 1. When the rail
break event occurs, it is typically characterized by a large energy
release that will cause an intrusion or disturbance of the
proximate sensing fiber 52 for one of the monitoring apparatuses
22, 24. As rail break events cause a large-magnitude energy release
over a short period of time (e.g., 200,000 psi in less than 2 ms),
the intrusion that these events cause to a sensing fiber is easily
distinguishable from other events which might also cause an
intrusion or disturbance of the fiber. Examples of such other
events include passing trains or vehicles and animals, which should
produce much smaller energy releases dispersed over a longer time
period (e.g., 100 psi over 100 ms). The signals produced by these
disturbances are subjected to wavelet analysis by signal analyzer
70 in order to detect and identify a spike or spikes having the
characteristic signature of a rail break.
[0056] The characteristic signature of a rail break can be
determined by simulation or by recording of an actual rail break
under simulated conditions, and the signatures of other potential
environmental intrusions can be measured as well. These signatures
can then be subjected to signal analysis to identify distinguishing
features of the signal produced during a rail break. Such a
procedure is understood by one of skill in the art. Among other
features, the short time duration and high magnitude of energy
release may be used to detect and identify a rail break event.
These features can be extracted via wavelet analysis, and those
events which do not possess these features can be screened out by
the signal analyzer 70. The signal analyzer 70 is programmed to
detect signals having substantially the same components and
characteristics as the recorded signal. Screening techniques are
used to screen out signals that do not have these unique components
and characteristics.
[0057] The monitoring assemblies 22, 24 are also capable of
establishing the approximate location of the rail break event, as
measured by the length of the sensing fiber.
[0058] In another aspect of the invention, the monitoring
assemblies 22, 24 are useful for detecting other identifiable
events, including the existence of flat spots on rail car wheels.
Such flat spots on the wheel circumference are undesirable since
they cause the train to become much more difficult to pull.
Further, such deformations in the wheel may damage the track rails,
ultimately leading to more rail breaks.
[0059] Operation of the system is essentially the same when used to
detect flat spots on wheels as that described earlier with respect
to the detection of rail break events. The energy signature
associated with the passage of trains having such flat spots
becomes the event of interest, and a signal representative of this
type of energy signature will be stored in the storage medium 80.
When a train having one or more wheels with flat circumference
spots travels along the track section 12, the flat spots
intermittently contact the track rails 14, 16 resulting in a
periodic energy signal. The periodic energy signal is transmitted
through the track and ground 32 to cause a disturbance of one of
the sensing fibers, such as fiber 52. The periodic energy signal is
detected in much the same manner as the rail break event energy
signature 100 was detected.
[0060] While preferred embodiments of this invention have been
shown and described, modifications thereof can be made by one
skilled in the art without departing from the spirit or teaching of
this invention. The embodiments described herein are exemplary only
and are not limiting. Many variations and modifications of the
system and apparatus are possible and are within the scope of the
invention. Accordingly, the scope of protection is not limited to
the embodiments described herein, but is only limited by the claims
that follow, the scope of which shall include all equivalents of
the subject matter of the claims.
* * * * *