U.S. patent application number 10/815385 was filed with the patent office on 2004-09-23 for cable fault detector.
Invention is credited to Eslambolchi, Hossein, Huffman, John Sinclair.
Application Number | 20040183545 10/815385 |
Document ID | / |
Family ID | 32312391 |
Filed Date | 2004-09-23 |
United States Patent
Application |
20040183545 |
Kind Code |
A1 |
Eslambolchi, Hossein ; et
al. |
September 23, 2004 |
Cable fault detector
Abstract
The present invention is a apparatus and method for accurately
finding a location of a fault in a fiber cable where a cable
locating current is leaking to ground. The system includes a sensor
body, voltage probes mounted in the body to face the cable, a
reference voltage input and a voltage comparator that compares the
reference voltage to a measured voltage at the probes. Use of the
system may include applying a conductive medium such as a
conductive gel between the probes and the cable.
Inventors: |
Eslambolchi, Hossein; (Los
Altos Hills, CA) ; Huffman, John Sinclair; (Conyers,
GA) |
Correspondence
Address: |
AT&T CORP.
P.O. BOX 4110
MIDDLETOWN
NJ
07748
US
|
Family ID: |
32312391 |
Appl. No.: |
10/815385 |
Filed: |
April 1, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10815385 |
Apr 1, 2004 |
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10379020 |
Mar 4, 2003 |
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6741081 |
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Current U.S.
Class: |
324/539 |
Current CPC
Class: |
H04B 10/0791 20130101;
H04B 10/07 20130101; G01R 31/083 20130101 |
Class at
Publication: |
324/539 |
International
Class: |
G01R 031/08; H04B
003/46 |
Claims
What is claimed is:
1. An apparatus for locating on an optical fiber cable a fault
where a cable locating current is leaking to ground, the apparatus
comprising: a body adapted to be positioned adjacent the cable; at
least one voltage probe mounted in the body and positioned in the
body to probe the leaking cable locating current; a reference
voltage input for receiving a reference voltage; and a voltage
comparator electrically connected to the at least one voltage probe
and to the reference voltage input, the comparator configured for
measuring a test voltage between the reference voltage and the at
least one voltage probe.
2. The apparatus of claim 1, wherein the body is further adapted to
at least partially surround a transverse section of the cable.
3. The apparatus of claim 2, wherein the at least one voltage probe
comprises a plurality of voltage probes angularly spaced around the
transverse section of the cable.
4. The apparatus of claim 1, wherein the at least one voltage probe
presents a conductive surface facing the cable.
5. The apparatus of claim 1, wherein the reference voltage is
ground.
6. The apparatus of claim 1, wherein the reference voltage is a DC
voltage applied to the cable.
7. A method for locating on a cable a fault where a cable locating
current is leaking to ground, the method comprising the steps of:
positioning a voltage probe adjacent the cable; applying a
conductive medium between the cable and the voltage probe;
displacing the voltage probe along the cable; measuring a voltage
between the voltage probe and a reference voltage; and based on the
voltage, detecting the fault at a position of the voltage probe
along the cable.
8. The method of claim 7, wherein the conductive medium is
water.
9. The method of claim 7, wherein the conductive medium is a
water-based paste.
10. The method of claim 7, wherein the conductive medium is a
gel.
11. The method of claim 7, wherein the voltage probe comprises a
plurality of conductive surfaces facing the cable.
12. The method of claim 11, wherein the step of positioning a
voltage probe adjacent the cable includes at least partially
surrounding the cable with the voltage probe.
13. The method of claim 12, wherein the step of displacing the
voltage probe along the cable comprises maintaining the probe in a
position at least partially surrounding the cable.
14. The method of claim 7, wherein the step of measuring a voltage
between the voltage probe and a reference voltage includes
measuring a voltage between the voltage probe and ground.
15. The method of claim 7, further comprising the step of applying
a reference DC voltage to the cable, and wherein the step of
measuring a voltage between the voltage probe and a reference
voltage includes measuring a voltage between the voltage probe and
the reference DC voltage.
16. The method of claim 7, further comprising the step of sounding
an alarm when the fault is detected.
17. The method of claim 7, further comprising the step of initially
determining an approximate position of the fault by determining a
position along the cable where an above-ground detectability of the
cable locating current degrades.
18. The method of claim 7, wherein the step of detecting the fault
comprises detecting a drop in the measured voltage.
19. The method of claim 7, wherein the step of detecting the fault
comprises detecting an increase in the measured voltage.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to the repair of
systems using a cable locating current for determining the position
of underground cables from above ground. More particularly, the
present invention is an apparatus and method for finding a fault in
a cable sheath that is causing the cable locating current to leak
to ground.
BACKGROUND OF THE INVENTION
[0002] Many utilities bury pipes and cables ("utility conveyances"
or "conveyances") underground for reasons of both safety and
aesthetics. Underground burial often provides protection to utility
conveyances against weather and other sources of potential damage.
Utilities that undertake burial of their conveyances usually make
extensive efforts to plot the location of each buried conveyance on
a map to facilitate its location in case of repair or replacement.
While a map will indicate the general location of a buried
conveyance, more precise location information often becomes
necessary, particularly in urban environments. For that reason,
most utilities that bury their conveyances underground rely on
electromagnetic signaling techniques to precisely locate such
conveyances.
[0003] U.S. Pat. No. 5,644,237, issued Jul. 1, 1997 and
incorporated herein by reference in its entirety, describes a
principle for electromagnetic signaling for locating a buried
utility conveyance. To locate a buried conveyance, a locating tone
or signal is applied to a metallic component of the conveyance. In
one currently used embodiment, the signal is an AC signal between
80 and 120 volts and having a frequency of from 220 to 440 Hz. As
shown in FIG. 1, in the case of a cable 100 containing fiber optic
bundles 110, a cable locating conductor may be included in the
cable as a metallic sheath 120 or a copper tracer wire (not shown)
within an insulating sheath 130 surrounding the cable. Using a
signal detector of a type well known in the art, a technician
locates the conveyance by operating the detector above ground to
detect a signal generated by current passing through the cable
locating conductor.
[0004] In addition to the AC locating tone, a DC cable locating
signal is also sometimes used in conjunction with a vector bar
detector in order to confirm the information from the AC signal.
The DC signal in a currently used system is approximately 80 to 100
volts.
[0005] The cable sheath or insulating sheath 130 surrounds the
cable locating conductor in the buried cable and insulates the
conductor from ground. The insulating sheath is applied during the
cable manufacturing process, and is formed from a durable, flexible
insulating material such as polypropylene. In one commonly used
fiber optic cable, the sheath 130 has a thickness 138 of
approximately 1/8 inch.
[0006] The insulating sheath of an underground cable has been known
to contain cable sheath faults such as fault 135 caused by
cracking, puncturing or preexisting manufacturing defects. Those
faults may permit water or other conducting media to penetrate the
cable, providing a ground path from the cable locating conductor
within the sheath. Sheath faults are most common in locations where
a cable is bent to a relatively small radius, such as within
manholes or splice boxes, where extra cable length is commonly
wrapped or coiled for later use in repairs or maintenance.
[0007] A cable sheath fault, once located, can often be repaired by
resealing the sheath in the area immediately surrounding the fault.
One commonly used method for repairing a sheath fault is by
wrapping a sealing tape around the area that includes the fault,
thereby sealing the leak. The tape may be a poly material and may
include an adhesive designed to withstand moisture and to adhere
securely to the sheath.
[0008] Cable sheath faults that are leaking current to ground may
be roughly located using outside plant fault detection equipment as
is known in the art. For example, a drop in the cable locating
signal received above ground usually indicates the presence of a
ground fault in that general area. Those techniques are effective
in isolating a sheath fault to a certain manhole or splice box. The
exact location of a cable sheath fault along a cable is, however,
very difficult to pinpoint even after it has been isolated to a
specific manhole or splice box. Manholes often fill with rainwater,
submerging the cable. When a cable is pulled from the water,
current flow to ground will often cease, making the fault difficult
to pinpoint. In many cases, the fault is not visible on the sheath
because the defect is extremely small or because a crack in the
sheath partially closes when the cable is unwound from a splice
box.
[0009] One technique frequently used by an outside plant technician
is to feel along the cable for any imperfection in the sheath.
Often, before the fault is detectable in that manner, the fault
must deteriorate significantly. That deterioration also makes it
impossible to use the cable locating current to locate the cable
underground in the event of a third party dig alert, cable
maintenance, cable repairs, etc. If a technician is not successful
in pinpointing the fault either tactilely or visually, it is not
possible to repair the sheath at the fault location. In those
cases, entire sections of cable, typically hundreds of feet between
splices, must be replaced.
[0010] There is therefore presently a need for a method and
apparatus for locating a sheath fault on a cable such as a fiber
cable, with sufficient precision to repair the fault without
replacing the entire section. To the inventors' knowledge, there is
currently no such apparatus or method currently employed to
satisfactorily accomplish that task.
SUMMARY OF THE INVENTION
[0011] The present invention addresses the needs described above by
providing a an apparatus and a method for locating on an optical
fiber cable a fault where a cable locating current is leaking to
ground. One embodiment of the invention is an apparatus for
locating such cable faults. The apparatus includes a body adapted
to be positioned adjacent the cable, at least one voltage probe
mounted in the body and positioned in the body to probe the leaking
cable locating current, a reference voltage input for receiving a
reference voltage, and a voltage comparator electrically connected
to the at least one voltage probe and to the reference voltage
input, the comparator configured for measuring a test voltage
between the reference voltage and the at least one voltage
probe.
[0012] The body may further be adapted to at least partially
surround a transverse section of the cable. In that case the at
least one voltage probe may be a plurality of voltage probes
angularly spaced around the transverse section of the cable. The at
least one voltage probe preferably presents a conductive surface
facing the cable.
[0013] The reference voltage may be ground, or may be a DC voltage
applied to the cable.
[0014] In another embodiment of the invention, a method is provided
for locating on a cable a fault where a cable locating current is
leaking to ground. The method includes the steps of positioning a
voltage probe adjacent the cable, applying a conductive medium
between the cable and the voltage probe, displacing the voltage
probe along the cable, measuring a voltage between the voltage
probe and a reference voltage, and, based on the voltage, detecting
the fault at a position of the voltage probe along the cable.
[0015] The conductive medium may be water, a water-based paste or a
gel. The voltage probe may include a plurality of conductive
surfaces facing the cable. In that case, the step of positioning a
voltage probe adjacent the cable may include at least partially
surrounding the cable with the voltage probe.
[0016] The step of displacing the voltage probe along the cable
preferably includes maintaining the probe in a position at least
partially surrounding the cable. The step of measuring a voltage
between the voltage probe and a reference voltage includes
measuring a voltage between the voltage probe and ground.
[0017] The method may further include the step of applying a
reference DC voltage to the cable. In that case, the step of
measuring a voltage between the voltage probe and a reference
voltage includes measuring a voltage between the voltage probe and
the reference DC voltage.
[0018] The method may include the step of sounding an alarm when
the fault is detected. An initial step may be included to determine
an approximate position of the fault by determining a position
along the cable where an above-ground detectability of the cable
locating current degrades.
[0019] The step of detecting the fault may include detecting a drop
in the measured voltage, or it may include detecting an increase in
the measured voltage.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 is a sectional view of an underground cable with a
sheath fault.
[0021] FIG. 2 is a view of an apparatus for locating sheath faults
according to the invention.
[0022] FIG. 3 is a flow chart illustrating a method for locating
sheath faults according to the invention.
DESCRIPTION OF THE INVENTION
[0023] An apparatus for precisely locating a cable sheath fault
according to the present invention is shown in FIG. 2. The
apparatus comprises a test set 210 that an outside plant technician
may place around a cable 205, and a voltage comparator 270 for
sensing electrical potential that may be present between the cable
205 and a reference voltage such as ground 275.
[0024] In a currently preferred embodiment of the invention, the
test set 210 comprises a generally cylindrical body 215 that
includes a slot or open area 216. The slot 216 is large enough to
permit the cable 205 to be inserted within the body 215 and placed
adjacent an inner surface 218 of the body. The body may then be
translated by a technician in directions 220, 221 parallel to an
axis of the cable 205 to test for sheath defects along a length of
the cable. The inner surface 218 of the body has a sufficiently
large diameter to leave a gap 225 of approximately 0.5-1.5 inches
of clearance between the surface and the exterior of the cable 205.
The body 215 is preferably configured to at least partially
surround the cable in a transverse plane, in order to facilitate
moving the body along the cable, and to increase the surface area
of the cable that is inspected as the body is translated along the
cable.
[0025] The body 215 is equipped with at least one voltage sensor
such as sensors 230a, 230b, 230c fixed to the inner surface 218 of
the body 215. The voltage sensors present conductive surfaces
facing the cable 205 in order to establish electrical continuity
between the sensors and the cable. The illustrated embodiment
includes three voltage sensors 230 that are equally spaced around
the circumference of the cable 205 in order to further enhance
continuity. One skilled in the art will recognize that other sensor
configurations may be used without departing from the spirit or
operation of the invention.
[0026] As discussed above, cable faults are frequently found on
cable lengths that have been wrapped or wound within a manhole or
splice box. Those environments are frequently filled with rainwater
or ground water. That water may provide a conductive path across
the gap 225 between the exterior surface of the cable 205 and the
sensors 230. If conditions are dry, or if a more sensitive
measurement is required, a conductive material such as a gel or
water based paste (not shown) may be applied to the cable to fill
the gap 225 and provide an enhanced conductive path.
[0027] The voltage comparator 270 measures electrical potential
between the sensors 230 and some reference voltage. In the
illustrated embodiment of the invention, the voltage is measured to
ground 275. That measurement is conveniently carried out by a
technician because a ground connection is almost always available
at the site.
[0028] In another embodiment of the invention, a reference voltage
is applied to the cable conductive element in addition to the cable
locating tone. The reference voltage may be a DC signal or may be
an AC signal having a different frequency than that of the cable
locating tone. While less convenient than using a ground reference,
the use of a delivered reference voltage assures that ambient
electrical potential that might be present in the local ground does
not affect the measurement. The apparatus of the invention may be
configured to use both reference voltage sources. Other reference
voltage sources may be used without departing from the scope of the
invention.
[0029] The voltage comparator 270 may be equipped with a visual,
audible or other signal indicating the presence of a fault.
Depending on the reference voltage used, the signal may alert the
technician to a sudden drop or rise in voltage, or both.
[0030] A method 300 for locating a fault on an optical fiber cable
according to one embodiment of the invention is illustrated in FIG.
3. The method is typically performed at a location such as a splice
box or manhole where a fault is suspected. The general location may
have been determined using above ground fault detection equipment.
A voltage probe is positioned (step 310) adjacent the cable. A body
containing one or more probes may be placed directly on the cable
as shown in FIG. 2, or may be of a type that must first be opened
in order to insert the cable. To improve the conductive path
between the probe and the cable, a conductive medium may be applied
(step 320) between the cable and the voltage probe. That medium may
be water, a water-based paste, or a gel. The conductive medium may
be applied to the probe, to the cable or to both, and may be
applied either before or after the probe is placed on the
cable.
[0031] The voltage probe is displaced (step 330) along the cable in
order to determine the exact location of the sheath fault. As the
probe is moved, a voltage is measured (step 340) between the
voltage probe and a reference voltage. As noted above, the
reference voltage may be ground or may be a voltage provided on the
cable locating conductor.
[0032] Based on the voltage, the fault is detected (step 350) at
the position of the voltage probe along the cable. The fault may be
signaled to the technician by an alarm or signal indicating a
sudden change in voltage as detected by the voltage comparator.
[0033] The foregoing Detailed Description is to be understood as
being in every respect illustrative and exemplary, but not
restrictive, and the scope of the invention disclosed herein is not
to be determined from the Detailed Description, but rather from the
claims as interpreted according to the full breadth permitted by
the patent laws. For example, while the system is described as
having a cylindrical body with circumferentially spaced probes,
other shapes and probe configurations may be used while remaining
within the scope of the invention. For example, the body may be
toroidal, horseshoe-shaped, or may simply be a handle for
presenting the probes. It is to be understood that the embodiments
shown and described herein are only illustrative of the principles
of the present invention and that various modifications may be
implemented by those skilled in the art without departing from the
scope and spirit of the invention.
* * * * *