Branched sensor system

A detection and location system, e.g. for liquid leaks, comprising a trunk line sensor cable and a plurality of branch line cables at intermediate points of the trunk cable. Each of the cables comprises two insulated conductors and two non-insulated conductors, e.g. conductive polymer-coated wires, which become connected upon occurrence of a leak. In one embodiment, each of the insulated conductors in the trunk line is continuous and each of the non-insulated conductors is discontinuous at each intermediate point; the branch line conductors are respectively connected to the discontinuous ends of the non-insulated trunk line conductors, and are connected in pairs of one insulated and one non-insulated conductor at the end of each branch. In another embodiment, in the trunk line, both the non-insulated conductors and one of the insulated conductors are continuous and one of the insulated conductors is discontinuous at each intermediate point; in the branch line, the two insulated conductors are respectively connected to the discontinuous ends of the insulated trunk line conductor at the intermediate point, and to each other at the end of the branch, and the two non-insulated conductors are respectively connected to the non-insulated trunk line conductors but are not otherwise connected.

BACKGROUND OF THE INVENTION 
Field of the Invention 
This invention relates to methods and apparatus for detecting and locating 
changes in variables. 
INTRODUCTION TO THE INVENTION 
Copending, commonly assigned U.S. patent application Ser. No. 832,562, 
filed Feb. 20, 1986, by Masia et al., the disclosure of which is 
incorporated herein by reference, discloses methods and apparatus for 
detecting and obtaining information about (particularly locating) changes 
in variables. Such changes are referred to in that application, and 
likewise in this application, by the generic term "event". In a preferred 
embodiment of such methods, and in other methods, there is used a sensor 
cable comprising two insulated wires and two "non-insulated" wires which 
are not connected to each other at any point along the length of the cable 
in the absence of an event but which become electrically connected to each 
other at some point along the length of the cable upon occurrence of an 
event. The non-insulated wires can for example comprise a metal core 
surrounded by a conductive polymer jacket, so that the wires become 
electrically connected if there is a water leak. The term "conductive 
polymer" is used herein to denote a composition which comprises a 
polymeric component (e.g. a thermoplastic, or an elastomer, or a mixture 
of two or more such polymers) and, dispersed in the polymeric component, a 
particulate conductive filler (e.g. carbon black, graphite, a metal 
powder, or two or more of these). The possibility of connection can for 
example exist at all points along an elongate path, or over selected 
stretches of an elongate path, or at discrete locations along an elongate 
path; for example the non-insulated wires can be wires which are insulated 
except at spaced locations and which can become connected at one or more 
of those locations through a switch which is switched on by occurrence of 
an event at the location of that switch. 
When such a four-wire sensor cable is used to detect events along a path 
comprising one or more branch paths extending from a main (or trunk) path, 
the cable can simply be routed along the branch path to the end of the 
branch path and then straight back to the trunk path. However, this can 
lead to misleading results, since an event taking place along the branch 
can cause connection of the non-insulated wires in both the outgoing 
branch cable and the incoming branch cable. This problem can be overcome 
by running the sensor cable from the junction of the trunk and branch 
paths to the end of the branch path only, and using four insulated 
"jumper" wires to make the appropriate connections from the end of the 
branch back to the trunk; but this is an expensive and inconvenient 
solution, especially when space is limited, e.g. in a double containment 
system. 
SUMMARY OF THE INVENTION 
We have now recognized that in a branched system using a four-wire sensor 
cable, the two insulated wires are not needed in the branch line to 
perform the functions for which they are needed when the four wire sensor 
cable is part of a trunk line, and that these insulated wires can, 
therefore, be used (a) as insulated jumper wires to connect the 
non-insulated wires between the junction of a branch and the end of a 
branch, or (b) can be connected to each other at the end of a branch and 
to incoming and outgoing ends of one of the insulated wires at the 
junction of a branch, thus providing a loop around the branch for 
continuity checking purposes. 
In a first embodiment of the invention, the insulated wires of the trunk 
cable are simply connected to each other across the junction; the 
non-insulated wires of the branch are connected (a) at the junction, to 
the non-insulated wires coming into (or going out of) the junction along 
the trunk path, and (b) at the end of the branch, to the insulated wires 
of the branch; and the insulated wires of the branch are connected at the 
junction to the non-insulated wires going out of (or coming into) the 
junction along the trunk path. In this way the errors which can occur with 
a simple loop system are substantially reduced or eliminated, as is the 
expense of the return leg of the four-wire sensor cable, or the 
inconvenience and expense of using separate jumper wires. Furthermore, the 
connections which have to be made at the end of the branch line can be the 
same as those made at the end of the trunk line, so that the same 
termination apparatus can be used. 
Accordingly, in one aspect, the present invention provides a sensor cable 
suitable for use in detecting and obtaining information about an event, 
the apparatus comprising 
(1) a trunk line cable which follows an elongate trunk path having a near 
end and a far end; and 
(2) at least one branch line cable which extends from the trunk line cable 
at an intermediate point along the trunk path and follows an elongate 
branch path from the intermediate point to a distant point; 
the trunk line cable comprising first, second, third and fourth elongate 
electrically conductive members, each of the first and second members 
running along the whole length of the trunk path but being discontinuous 
at each intermediate point to provide an incoming end nearer to the near 
end of the trunk path and an outgoing end nearer to the far end of the 
trunk path, and each of the third and fourth members running continuously 
along the whole length of the trunk path; 
the branch line cable comprising fifth, sixth, seventh and eighth elongate 
electrically conductive members, each of which runs continuously along the 
whole length of the branch path and has a first end at the intermediate 
point and a second end at the distant point; 
each of the first ends of the fifth, sixth, seventh and eighth members 
being respectively connected to one of the incoming and outgoing ends of 
the first and second members, the second ends of the fifth and sixth 
members being respectively connected to the second ends of the seventh and 
eighth members, so that the incoming and outgoing ends of the first member 
are electrically connected to each other through the branch line cable and 
the incoming and outgoing ends of the second member are electrically 
connected to each other through the branch line cable; 
the first and second members being, in the absence of an event, insulated 
from each other and from other components of the trunk line cable along 
the length of the trunk line cable except for said connections at each 
intermediate point, and optionally being such that upon occurrence of an 
event at a point along the trunk path, electrical connection is made 
between the first and second members at that point; 
the third and fourth members being such that they are electrically 
insulated from each other and from other components of the trunk line 
cable along the length of the trunk line cable, both in the absence of an 
event and upon occurrence of an event; 
the fifth and sixth members being, in the absence of an event, insulated 
from each other and from other components of the branch line cable along 
the length of the branch line cable, except for said connections at each 
intermediate point and distant point, and being such that upon occurrence 
of an event at a point along the branch path, electrical connection is 
made between the fifth and sixth members at that point; and 
the seventh and eighth members being such that, both in the absence of an 
event and upon occurrence of an event, they are electrically insulated 
from each other and from other components of the branch line cable along 
the length of the branch line cable, except for said connections at each 
intermediate point and distant point. 
In a second embodiment of the invention, wherein a four-wire sensor cable 
provides branches for detection of an event (and for location of the 
branch along which the event has occurred, but not for identifying the 
point along the branch at which the event occurred), there is provided a 
sensor cable for use in detecting and obtaining information about an 
event, the cable comprising 
(1) a trunk line cable which follows an elongate trunk path having a near 
end and a far end; and 
(2) at least one branch line cable which extends from the trunk line cable 
at an intermediate point along the trunk path and follows an elongate 
branch path from the intermediate point to a distant point; 
the trunk line cable comprising first, second, third and fourth elongate 
electrically conductive members, each of the first and second members 
running continuously along the whole length of the trunk path, one of the 
third and fourth members running continuously along the whole length of 
the trunk path, and the other of the third and fourth members running 
along the whole length of the trunk path but being discontinuous at each 
intermediate point to provide an incoming end nearer to the near end of 
the trunk path and an outgoing end nearer to the far end of the trunk 
path; 
the branch line cable comprising fifth, sixth, seventh and eighth elongate 
electrically conductive members, each of which runs continuously along the 
whole length of the branch path and has a first end at the intermediate 
point and a second end at the distant point; 
the first end of the fifth member being connected to the first member at 
the intermediate point, the first end of the sixth member being connected 
to the second member at the intermediate point, the first end of the 
seventh member being connected to the incoming end of the third or fourth 
member, the first end of the eighth member being connected to the outgoing 
end of the third or fourth member, and the second ends of the seventh and 
eighth members being connected to each other at the distant point; 
the first and second members being, in the absence of an event, insulated 
from each other and from other components of the trunk line cable along 
the length of the trunk line cable, except for said connections at each 
intermediate point, and optionally being such that upon occurrence of an 
event at a point along the trunk path, electrical connection is made 
between the first and second members at that point; 
the third and fourth members being such that they are electrically 
insulated from each other and from other components of the trunk line 
cable along the length of the trunk line cable, except for said 
connections at each intermediate point, both in the absence of an event 
and upon occurrence of an event; 
the fifth and sixth members being, in the absence of an event, insulated 
from each other and from other components of the branch line cable along 
the length of the branch line cable, except for said connections at each 
intermediate point, and being such that upon occurrence of an event at a 
point along the branch path, electrical connection is made between the 
fifth and sixth members at that point; and 
the seventh and eighth members being such that, both in the absence of an 
event and upon occurrence of an event, they are electrically insulated 
from each other and from other components of the branch line cable along 
the length of the branch line cable, except for said connections at each 
intermediate point and distant point. 
The novel sensor cables of the invention preferably form part of an 
apparatus for detecting and locating an event which comprises 
(A) a power source; 
(B) a voltage measuring device, and 
(C) a sensor cable as defined above. 
In the case of a sensor cable according to the first embodiment of the 
invention, for example, the apparatus is preferably such that, upon 
occurrence of an event at a location along the cable, an electrical 
connection is made at that location either between the first and second 
members or between the fifth and sixth members; and the making of said 
connection resulting in a system in which 
(i) the first member is electrically connected (a) at the near end of the 
trunk path, to the power source and to the voltage-measuring device, and 
(b) at the far end of the trunk path, to the third member; 
(ii) the third member is electrically connected (a) at the near end of the 
trunk path, to the voltage-measuring device, and (b) at the far end of the 
trunk path, to the first member; 
(iii) the fourth member is electrically connected (a) at the near end of 
the trunk path, to the power source, and (b) at the far end of the trunk 
path, to the second member; 
(iv) there is a test circuit in which a current of known size flows and 
which comprises 
(a) those parts of the second, sixth and seventh members which lie between 
the connection point and the far end of the trunk path, 
(b) the connection; 
(c) those parts of the first, fifth and eighth members which lie between 
the connection point and the near end of the trunk path, 
(d) the fourth member of the trunk cable, and 
(e) the power source, and 
(v) there is a reference circuit which comprises 
(a) the first, fifth and eighth members, 
(b) the third member, and 
(c) the voltage-measuring device; 
whereby the voltage measured by the voltage-measuring device can be used to 
determine the location of the connection point. If desired, the apparatus 
can be such that, in the absence of an event, no current flows through any 
of the first to eighth elongate members. Alternatively, in the absence of 
an event, there can be a current which flows through one or more of the 
members, either continuously or intermittently, e.g. for checking 
continuity, preferably a current which is relatively low by comparison 
with the current of known size which flows in the test circuit. 
In preferred apparatus of this kind, at all points on the sensor cable at 
which occurrence of an event can cause connection between the first and 
second members or the fifth and sixth members, the sum of (a) the 
resistances of the first, fifth and eighth members and any resistors in 
series therewith, between the near end and the connection point, and (b) 
the resistances of the second, sixth and seventh members and any resistors 
in series therewith, between the connection point and the far end, is 
substantially independent of the location of the connection point. 
In order to achieve this result, it is preferred that 
(i) the incoming ends of the first and second members at each intermediate 
point are connected to the first ends of the fifth and sixth members 
respectively, or to the first ends of the seventh and eighth members 
respectively; 
(ii) the outgoing ends of the first and second members at each intermediate 
point are connected to the first ends of the eighth and seventh members 
respectively, or to the first ends of the fifth and sixth members 
respectively, 
(iii) the second ends of the fifth and eighth members are connected at each 
distant point; and 
(iv) the second ends of the sixth and seventh members being connected at 
each distant point. 
The trunk line cable comprises first, second, third and fourth elongate 
electrically conductive members. For any segments of the trunk line along 
which detection of an event is not required, the cable can simply comprise 
four insulated wires which are of low resistance. For any extended 
segments along which detection of an event is required, the trunk line 
cable can comprise two low resistance insulated wires and two high 
resistance conductive-polymercoated wires which become electrically 
connected to each other if an event occurs, eg. a leak of water or another 
electrolyte, or a leak of a hydrocarbon or other organic fluid which 
causes swelling of a component in the cable, thus effecting electrical 
connection; the high resistance wires are preferably identical and have a 
resistance per unit length which is substantially invariable under the 
operating conditions. The trunk line cable can also comprise spaced-apart 
locations at which connection between the source and locating members 
takes place upon occurrence of an event, eg. through the operation of 
switch. One form of switch is a pair of conductive-polymer-coated wires 
which extend from the trunk cable; one wire is connected to the source 
member and the other to the locating member. The pair of wires can be part 
of a zone cable which extends from the trunk cable and which comprises in 
addition two insulated low resistance wires which are connected as a loop 
to form part of the return member and thus enable the continuity of the 
system to be checked. Other possible features of the branch line cable are 
described in patent application Ser. No. 057,459. 
The branch line cable can have the same characteristics as are described 
above for the trunk line cable, except that at least part of the branch 
line comprises members which, upon occurrence of an event, become 
electrically connected. However, the invention is particularly useful when 
the branch line cable comprises two low resistance insulated wires (which 
may be the same or different) and two conductive-polymer-coated wires 
(which are preferably the same), particularly when at least part of the 
trunk line cable has substantially the same physical construction as the 
branch line cable. Particularly under such circumstances, it is preferred 
to put resistors in the connections between the conductive-polymer-coated 
wires; this results in discontinuities in the possible readings of the 
voltage-measuring device, so that despite a small error in the reading, 
the location of the event can be identified as being in the trunk line or 
branch line, as the case may be. 
A very useful attribute of the apparatus of the present invention is that 
is can be assembled at an installation site from pre-terminated cables and 
preassembled connection and termination units which can be manufactured in 
a factory, thus eliminated the need to carry out in situ wiring, with the 
attendant risk of error. The various connection and termination units can 
be assembled (and if desired sealed) as flexible harnesses or in boxes.

DETAILED DESCRIPTION OF THE INVENTION 
Referring now to the drawing, each of the Figures is a circuit diagram of 
an apparatus of the invention which comprises 
(A) a constant current power supply (100); 
(B) a high impedance voltmeter (200); 
(C) a trunk line cable which has a near end (300) and a far end (400), and 
which is made up of a plurality of segments, each segment comprising a 
first member (11, 12, 13 etc.), a second member (21, 22, 23 etc.), a third 
member (31, 32, 33 etc.) and a fourth member (41, 42, 43 etc.); and 
(D) at least one branch line cable which extends from an intermediate point 
(500) along the trunk path to a distant point (600) and which is made up 
of one or more segments, each segment comprising a fifth member (51, 52, 
53 etc.), a sixth member (61, 62, 63 etc.), a seventh member (71, 72, 73 
etc.) and an eighth member (81, 82, 83 etc.). 
In each of the Figures, the phantom lines enclose components which can 
conveniently be preassembled in a manufacturing facility (eg. as a box or 
a flexiblle harness), with appropriate connecting means for the cables 
which make up the rest of the apparatus. The pre-assembled parts and the 
cables can then be assembled at the site of the installation. 
Referring now to FIG. 1, this comprises a trunk line cable having two 
identical branch line cables connected thereto in accordance with the 
first embodiment of the invention. The segment of the trunk line cable 
closest to the near end 300 comprises four low resistance insulated wires 
11, 21, 31 and 41 and extends along a path along which detection of an 
event is not required. The second, third and fourth segments of trunk line 
cable comprise two low resistance insulated wires 32, 33 and 34, and 42, 
43 and 44, and two identical high resistance conductive-polymer-coated 
wires 12, 13 and 14, and 22, 23 and 24 which become connected to each 
other if an event occurs, e.g. a leak of water or a hydrocarbon. At each 
intermediate point 500, the trunk line cable and the branch line cable are 
connected to a preassembled T-connector 501 which will not detect 
occurrence of an event, which makes the connections shown, and which 
includes four identical resistors 1, 2, 3 and 4. The branch line cable has 
a single segment which runs from the intermediate point 500 to the distant 
point 600 and which has the same physical construction as the second 
segment of the trunk line cable and comprises two low resistance insulated 
wires 71 and 81 and two identical high resistance 
conductive-polymer-coated wires 51 and 61 which become connected to each 
other if an event occurs. At the distant point 600, the branch line cable 
is connected to a preassembled terminator 601 which makes the connections 
shown. The final segment of the trunk line cable is connected to a 
preassembled terminator 602 which makes the connections shown and which 
can be identical to terminator 601. 
The wires 11, 12, 51 and 13, the resistors 1 and 2, and the connections 
between them together form a locating member. The wires 21, 22, 61 and 23, 
the resistors 3 and 4, and the connections between them together form a 
source member. 
When the occurrence of an event causes a connection to be made at a single 
point along the trunk or branch line cables (i.e. between members 12 and 
22, or members 51 and 61, or members 13 and 23), the voltage measured by 
the voltmeter depends upon the resistance of the locating member between 
the near end 300 and the connection point. Through knowledge of the 
resistance per unit length of the various components, or through prior 
mapping of the system, the measured voltage indicates the location of the 
event. The resistors 1, 2, 3 and 4 ensure that, despite a small error in 
the voltage measurement, an operator can distinguish between an event at 
an end of the trunk line cable close to a T-connector and an event at the 
end of a branch line cable close to a T-connector or at the end of a 
branch cable close to a terminator 601. 
In FIG. 1, the connections in the T-connector are between members 51 and 
12, 61 and 22, 71 and 23, and 81 and 13. However, since the members 71 and 
81 have much lower resistance than the members 51 and 61, results which 
are substantially the same could be obtained by making the connections 
between 51 and 12 (as before), 81 and 13 (as before), 61 and 23, and 71 
and 22; and results which are equally accurate, or substantially as 
accurate, but in which locations on the branch line were measured from the 
distant point instead of the intermediate point, could be obtained by 
making the connections between 12 and 71, 22 and 81, 51 and 23, and 61 and 
13 (equally accurate) or between 12 and 71, 22 and 51, 81 and 23, and 61 
and 13 (substantially as accurate). 
FIG. 1 shows two branch lines, but there could be any number of branch 
lines. 
Referring now to FIG. 2, this shows a system in accordance with the second 
embodiment of the invention which will detect the occurrence of an event 
in one of a plurality of zones, but not elsewhere, and will identify the 
zone in which the event took place, but will not identify the location of 
the event in the zone. Between the zones, both the trunk line cable and 
the branch line cable comprise four insulated low resistance wires. In 
each zone, a first conductivepolymer-coated wire extends from the locating 
member, and a second conductive-polymer-coated wire extends from the 
source member, close to but not touching the first wire; upon occurrence 
of an event anywhere in the zone, the first and second wires are brought 
into electrical contact, thus connecting the source and locating members. 
Resistors are placed in the locating member so that the voltage measured 
by the voltmeter identifies the zone in which an event has taken place, 
and balancing resistors are placed in the source member. 
The segment of the trunk line cable closest to the near end 300 comprises 
four low resistance wires 11, 21, 31 and 41. At the intermediate point 
500, the trunk line cable and the branch line cable are connected to a 
pre-assembled T-connector 501 which makes the connections shown. The first 
segment of the branch line cable has the same physical construction as the 
trunk line cable and contains four low resistance insulated wires, and is 
connected to a T-zone connector 701, which makes the connections shown 
between a zone cable and the first and second segments of the branch line 
cable, and which contains resistors 5 and 6. The zone cable has the same 
physical construction as the branch line cable of FIG. 1, and contains two 
low resistance insulated wires 171 and 181 and two 
conductive-polymer-coated wires 151 and 161. It is, however, connected 
differently both at the T-zone connector 701 and at the zone terminator 
801; the wires 171 and 181 are connected as a loop between insulated wires 
81 and 82 so that it is possible to make a continuity check of the zone 
cable. The second segment of the branch line cable likewise contains four 
insulated wires 52, 62, 72 and 82. The second segment is connected to 
another T-zone connector 702 which is the same as 701 and to which is 
connected a second zone cable comprising insulated wires 271 and 281 and 
conductivepolymer-coated wires 251 and 261 and terminating in zone 
terminator 802. Terminator 603, which can be the same as terminator 601 
used in FIG. 1 makes the appropriate connections at the end of the branch 
line. 
The second segment of the trunk line cable, comprising four insulated wires 
12, 22, 32 and 42, is connected via an end zone connector 901 to a zone 
cable which is like that in the other zones, which comprises two insulated 
wires 371 and 381 and two conductive-polymer-coated wires 351 and 361, and 
which is connected to zone terminator 803.