CA1225256A - Method for detecting and locating changes in ambient conditions - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

Method and apparatus for detecting and obtaining information about (particularly locating) an event, i.e. a change in a variable, for example an increase in the concentration of a fluid as the result of a leak, a change in the physical position of a movable member such as a valve, a change in temperature, or a change in pressure. In a preferred embodiment, two conductors follow an elongate path and are connected to each other at one end through a constant current source. In the absence of an event, the two conductors are electric-cally insulated from each other at all points along the path. When an event occurs, the two conductors become electrically connected at a connection point at which the event occurs, thus completing a circuit in which a current of known size then flows. The size of the current dots not depend on the resistance of the connection. One of the conductors is a locating member having known impedance characteristics along its length, and by measuring the voltage drop between the connection point and one end of the locating member the location of the event can be calculated.

Description

aye so BACKGROUND OF THE INVENTION

Field of the Invention .. . . _ . . .
This invention relates to methods and apparatus for detecting and obtaining information about (particularly locating) changes in variables.
Introduction to the Invention A number of methods have been used (or proposed for use) to detect changes in variables along an elongate path, e.g., the occurrence of a leak (of water or another liquid or gas, insufficient or excessive pressure, too high or too low a them-portray, the presence or absence of light or another form of electromagnetic radiation, or a change in the physical position of a movable member, e.g. r a valve in a chemical process plant or a window in a building fitted with a burglar alarm system.
Changes of this kind are referred to in this specification by the generic term "event". Such detection methods are for example highly desirable to detect leaks from steam lines into thermal insulation surrounding such lines, leaks from tanks and pipes containing corrosive or noxious chemicals, or leakage or condemn-station of water under floors or within telecommunication or electrical power systems. Some of these known methods not only signal when the event takes place/ but also indicate the location of the event. However, the known methods which indicate the location of the event suffer from serious disadvantages. For I ~2~2~6 example, they make use of time domain reflectometer techniques (and are, therefore, expensive), and/or give unreliable results when used over usefully long elongate paths or under conditions when there may be a substantial and unknown variation along the length of the path of a variable which affects the accuracy of the measurement (especially temperature), and/or make use of electrical conductors whose primary purpose it to carry a current (e.g., a telecommunication signal under normal operating con-dictions (and which therefore have resistance and uniformity characteristics consistent with that purpose), and/or cannot be used when the event causes electrical connection between two conductors through a connection which is of high or inditer-minute resistance, e.g., an tonically conductive connecting element. Reference may be made for example to United States Patents Nos. 1,084,910, 2,581,213, 3,248,646, 3,384,493, 3,800,216, and 3,991,413, United Kingdom Patent No. 1,481,850 and German Offenlegungschriften Nos. 3,001,150.0 and 3,225,742.
SUMMARY OF THE INVENTION
In accordance with the present invention, we have now discovered an improved method and apparatus for monitoring for the occurrence of an event and for detecting and obtaining information about the event upon its occurrence (i.e., as soon as it occurs or at some time after it has occurred). In this method, ..~

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upon o~urrence Do the event, at lest one electrical connection it made between Doris member end 8 locating ember ox known i~pedence corrector Tao the connection or connection being effective at n first point at which the event tykes place (or whose locution it defined by Bore other oharacteri6tic ox the event A current of known size it then driven through the electrical connection and town the locating member to a second print whose locution it known. The voltage drop between the first and ~ecsnd points it then measured end the locution of the first point can then be determined. the system preferably makes use of a locating member hiving an impedance which is selected to give desired degree of 3rcuracy in locating the first print, end which preferably does not very subst~nt-tally within the temperature range in which the system operate.

hen the occurrence of the overt onuses a single or very short connection to be mode between the locating 20 member and the source member, then the "first point"
Jill of course be easily identi~ieJ, since it it the only connect point. However, when the event results - in connection acted or Gore spcced-apart lccati~ns and/or over finite length of the locating member the First pontoon . the point whose lDc~tion eon be determined prom the observed volt drop, is owe intermediate point which can conveniently be referred to en the Electrical center of the various connections.
If there are connection it two or more spaced-apart 30 locations, the electoral center" may be sty e location at which there it no connection between the locating Ed source menders. It is for this reason that the connection to the toasting member is onetime referred to herein as being effective" at the first point.

2~2S6 . -5-i HDwe-~er, it it; to be understood that where reference is jade her o the ccnne~ti~n being jade" et the first point, this it intended to include situ~ti~n~ in which a plurality of electrical oonn~ctions are sue between the locating member end the source member, with the electrical center of the sanction being at the first point. In many Chihuahuas, the first point will be at, or clove to, that point at which e connection is made and which it closest ED the second point; however, it is important to realize that this it not necessarily the case .

he invention overcome one or more of the disadvantage of the known processes. For many uses, a particularly important advantage it that the information obtained can be independent of the impedance of the connection to the locating member, i.e. the infornatinn obtained remains the save even if a sub6tantiel sod unknown change it made in the impedance of the connection.

In one aspect t the invention provides a method for monitoring for the occurrence of an event, sod or detecting God obtaining information about the event upon its occurrence which method comprises providing a system in which, upon Dccurrenre Do the event, (1) electrical connection 8 made between us electrically conductive kowtowing member and an electrically conductive sourer member;

the connection to the locating member being effective at a first print whose location is defined by et least one characteristic of the event;

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the making of the connection enabling the fourteen of a text circuit which caprices (I the connection, (b) that part of the locating umber which lips bæt~c~n the first point and a second point having a known location on the locating member, and (c) a power source which cause an electrical current of known foe to be transited between the first end second point on the locating member; end the current end the locating member being such that, by measuring the voltage drop between the first and second points the spatial relationship between the first and second point con be determined;

(2) the voltage drop between the forfeit and end points is erred; on I information concerning the event it obtained from the measurement jade in to I

Preferably the voltage drop between the first and second point it determined by jeans of a voltage-erring dsvico which form part of a reference irrupt, the reference circuit comprising I) the volta~e-~oasuring device (b) that part of the locating member which lit - between the first end second point, end (c) on electrically conductive return member which (i) it electrically connected to the locating member at thy second print and at soother point on the locating member whose distance MP0&69 - ~22~5~

fry the secDn~ point is it least en great as the dunce iron the second point to the first put, hot distance being measured along the locating member, end it I
otherwise insulated from the locating member 9 the volt~ge-me~suring device hiving an impedance which is very high ho comparison with any unknown port of the impedance of the other components of the reference circuit.

. the invention alto includes apparatus suitable for carrying out the method of the invention in particular apparatus comprising (1) an elongate electrically conductive locating member whose impedance from one end to any point on the locating member defines the spatial relationship between that end and that point;

(2) an elongate electrically conductive source ! member;

(3) on event-sensitive connection means which, upon occurrence of sun event, effects electrical connection between the locating member end the source member, the connection being effective it a first point on the locating member which to defined by at lust one chsr~cteristic of the vent;

(4) voltegs-me~suring device for determining the voltage drop between the first point sod a second point which it it one end of the loosing member; and -B - .
Sue I power source which it electrically connected Jo the Elecond point on the lofting Norway end which, in the absence of sun event, I riot otherwise connected to the locating member, so that, when occurrence of on event causes sun electrical connection to be made between the locating and source eerily this enable the formation of a text circuit which comprises (~) the connection, (b) that part of the locating member which I Lowe between the first end second points, and I the power source, end in which test circuit e current of known size is transmitted between the first and second points on the locating member.

The invention alto includes novel elongate articles which can be used in the method end apparatus of the invention in particular articles which comprise (A) sun elongate ore which is composed of metal whose temperature coefficient of resistlvity overages Lowe than 0.003 per degree Centigrade over - the temperature range 0 to 100C end in .. which each longitudinal section has e resistance high is from 10 4 in 104 ohms/ font and (B) an elongate jacket which is composed no a conductive polymer which electoral surrounds the core, and in which each longitude final section has 8 resistance which is et least lD0 times the resistance of the core of that longitudinal section By all tempers-lures from 0 to lode go ~225;~:S~

Aries DES~RIPIlOtS I TOE CROWING
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ye inven~lon lo illustrated in the scco~panying drawing, on which Figure l is a generalized schematic circuit diagram of the method of the present invention, Figures 2-24 are ~chemstic circuit diagrams of the method and apparatus of the invention, Figure 25-27 are graphs showing how the voltage drop between the first and second points on the looting member con vary in different systems of the invention, end inure 28-33 are diagrammatic cro~s-sections through apparatus of the invention.

DETAILED DESCRIPTION OF THY INVENTION
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In the interests of laureate the following detailed description of the invention include sections which are off or exclusively concerned with a particular port of the invention. It it to be understood, however, that the relationship between different part of the 20 invention it of s~nificant importune, and the following detailed description should be rest in the light of that understanding. It should also be understood that, where features of the invention are described in the context of particular Figures of the drawing, the same I description con ~15D be applied to the invention in general and to the other Figures, insofar us the context permit I
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1. TOE ELECTRICAL CHARACTERISTICS OF THE INVENTION
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he basic electrical char~cteristic6 of the invention can bet be understood by reference to Figure 1, which schematically represents a sub6t~nti~1 number of the preferred methods and apart of the invention. In Figure I, there i an elongate lDceting Dumber 11, on elongate source member 12, e voltage-erring device 14, power source 15 end an elongate return member 16. the source member it electrically . connected, through the power sure to one end of the locating member; in the absence of on event, there is no Dither electrical connection between the locating member and the source member. Between the course end locating members (but not shown in Figure 1) it an event sensitive connection ennui (this term being used to include a continuous event-sen~itive connection means and a plurality of ~peced-ap~rt event-~en~itive connection means) which becomes conductive it any location at which an event take place In Figure 1, I an event his token place at a final point 1 which lies somewhere on the locating member, but whose location it other unknown. As-a result ox the event, an electrical connection E his been jade between the locating end source member. The power source 15 it connected via connection ennui 152 to the toasting member at one end thereof, designated by the numeral 2 which is the "second point" in two definitions given above of the method and epparetus of the invention.
(Th~.secDnd point could be it any point of known locution between the end of toasting member 11 end the connection point 1, providing that the voltage-meesurin~
device it 3rrsnged to measure the voltage drop between the first and second pointer) The power source it also connected to the source member; US Schematically indicted by the plurality of connection 151, the MPU~69 L~:5;25~

connection between thy power source and the source eyebrow can be ye it sty one or Gore points on the source err, Further the ~Dnnection~ cfln be of err end unknown pudency, providing the power source con drive a known current between the first and end points of the locating member. Thus the making of the connection at point 1 results in the formation of 3 test circuit which includes the connection, the toasting member between points 1 and 2, the power source and (unwell a jingle connection 151 it made between the pies source nod the source member at the connection point part of the source member.

The v~ltage-mes~uring device it connected to the second point 2 on the locating member (via the return member 16) and it also connected to the locating member at one or more point whose distance from the second point is it lest us far us the first point 1, as schematically indicated by the plurality of connections 141, these connection mutt be of known impedance or sun ED impedance which is very small by comparison with the impedance of the volt~ge-measuring device. Thus the voltage-measuring device forms part of a reference circuit which comprises the device it least that part of the locating member between points 1 and 2, and top return member.

he power source 15 end the voltage-meRsuring device 14 own be connected to the point on the toasting member 11 in any convenient Jay. Thus, so indicated by the plurality of connections 153, the ED connection member 152 and the return member 16 can be connected to each other at any one or more locutions.

It will be teen that the locution of print 1 can be calculated of the following are known:--12~ 525~

(a) thy current phony between points and 2, (b) the pudency ox the ~o~pDnents of the reference circuit, (c) the voltage drop measured by the voltage-measuring device, (d) the location of point 2, and (I thy i~pedanre of the locating member between print 2 end etch point on the lDcsting member.

Systems in which these features are known con be provided in a number of different aye. The accuracy with which the first point can be located is limited by the ratio of the impudency of the voltage-measuring device to any unknown part of the impudence of the other components of the reference circuit; and in most cases it is convenient to use component such that the ratio of the impedance of the device to the total impedance of the ret of the reference circuit is very high, Accordingly, these ratio should preferably be it least 100, particulfirly it least Lowe, especially at least Lydia. It I for these reasons tint the connection 141 and 153 on Figure 4 ore shown I having ID resistance. by counterweight the ruttiness of the .. Connection between the locating and Ursa members, sod the rustiness of the other components of the text circuit do nut affect the accuracy of the information - obtained; this is on important advantage of the invention.

2; INFORMATION WHICH CAN YE PROVIDED ABOUT AN EVENT

, The method of the invention not only detect that a particular event has taken plower but sly provides information bout the event. In many case, the information provided bout the event is it location, particularly when the vent takes place et (or near) the locution ox the first point.

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over, gee infuriation providet1 con be Dither inform lion; jot expel ho the ~e~perat~ t a particular location Swing ~onitu~ed7 Dyne pin on thy locating umber can be identified when the temperature I in one temperature range an another point eon be identified when the temperature it in n different temperature range. As jut noted, the locution of the event may be at, Dry clue to, the first point on the locating member. Hs~ev~ it it not necessarily so; for example, one or ore remote event-detecting stations can be connected electrically or otherwise 9 to different points on n central toasting member, the locations of the connection punt being ch~rncteristic of the locations of the event-detecting stations. the method of the invention will provide some, but nut niece ssrily 9119 the desired information about the event. For example, the method can usefully be employed to determine that a given event (e.g. the opening of a valve) has token place at one or Gore Do a relatively smell number of different locutions, out of a relatively large number of possible locations for the event, leaving it to visual inspection or some other form of test (which ! may be a further end different method of the invention to determine precisely where the event has token piece.

3. EVENTS WHICH CAN BE DETECTED, AND EVENT-SENSITIVE

The event which By detected in the method of the invention can by an event which nut desired ( 8 fault) or an event which it desired. The event can be the existence of particular condition or a change in a single variable, e.g. nun inquiries in pressure above a particular vnlue9 or n simultaneous or sequential change in two or more variables, e.g. an increase in pressure accompanied by on inquiries in temperature.

MP~B69 ~14-~2~2~1~
The vet on be change in R variable which lasts for only very shout time, Do a huge on 3 variable which is maintained for Rome iamb tire. the vent can be of any kind which director or indirectly permits or S Swiss the current to be transmitted between the first point nod the second point on the locating member. As noted above, the information obtained it independent of the i~pedancs of ho connection. Thus the connection between toe locating and source member can be of any ED kind, for example an electronic connection (which can be of substantially Nero impedance or con hove substantial impudency or on ionic connection resulting from the presence of on electrolyte, so an inductive connection.
The change which takes piece in order to effect the connection between the locating and source conductors is preferably c revertible change. However 9 the invention it ~180 useful when the change is a p~r~Qnent one, 80 that the apparatus Utah be replaced or repaired before the stem it operational Gwen. The system can I be arranged 80 that it signal an event only while the spent it taking place or 80 that it signal that on event has occurred in the pest; in the litter case, the 8yst~m will normally be arranged By that it con be reset.

Examples of event which can be detected include, but are not limited to, the following.

A. The presence of water or another electrolyte which provides sun ionic connection between exposed surfaces of the locating sod uric members, especially when at least part of at least one of these comprises 2 metal core surrounded by e conductive polymer. In this cave, the cvent-sensitive connection means can be merely c space between the locating end source members, or it can be e connection member on which the electrolyte collects or Shea absorbs the electrolyte.

MP0~6 ~22~ it . Foe existence of t~pe~ture which it below fret temper e I or Eve a second temperature To. In one apparatus detecting such a condition the looting and source members are physically contacted by a connecting member which insulates them from etch other it To and connects them to etch other at To.
For example, it least part of the connecting member can comprise (~) first stalely and (b) a second material which it dispersed in the first material and which form mobile ionic push when the temoer~ture change from To to To. Thus the first material can be one which change posse, e.g. melt, when the temperature changes from I to I

In another apparatus for detecting a temperature change, the locating and Ursa members are separated from each Dither by a deformable insulating medium, e.g.
en insulating medium which is at least in port 8 fluid, ego sir, end the apparatus comprises a connecting member which change shape when the temperature changes 2û prom I to To thus forcing the member into contact, by deforming the insulating tedium, or, if the connecting member is itself conductive, by Forming the connecting member through the insulting medium to connect the members. The c~nneoting member can comprise a heat-recoverable polymer or a heat-recoverable memory Mets or can comprise a bimetallic trip. ohs term memory metal is used herein to denote one of the metal alloys (in particular various brews alloys and nickel-titanium alloys) which exist in 8 strong gusted-ED tic state above a transformation temperature end in weak mertensitic state below that transformation temperature, and which, if fabricated in a first shape in the ~ustenitic tote can be cooled to the martensitic state and then deformed 9 wilt retain the deformed -16~ ~2~2~

configuration until reheated to the austenitic state, when they will revert (or attempt to revert) towards the original shape.
Where a reversible effect is desired, a particular type of memory metal must be employed or the memory metal member can be combined with a conventional spring metal member to produce a connecting member which will connect the locating and source members either when the temperature rises above the transformation them-portray or when it falls below the transformation temperature (as more specifically discussed below, in connection with the Figures). For further details of memory metals and devices come prosing them, reference may be made for example to United States Patents Nos. 3,174,851, 3,740,839, 3,753,700, 4,036,669, 4,144,104, 4,146,392, 4,166,739 and 4,337,090.
C. A change in the concentration of a particular substance, which may for example be a gas, a liquid or a solid dispersed in a gas or a liquid, the locating and source members being physical-lye contacted by a connecting member which insulates them prior to said change, and which electrically connects them as a result of said change. The electrical connection can for example result from a chemical reaction between the substance and at least part of the connecting member, thus for example releasing a mobile ionic species. Alternatively, the presence of the substance can for example cause at least part of the connecting member to change shape, as for example where the substance causes swelling of a conductive polymer connecting member or where the substance is a solvent for an adhesive or polymeric retaining member which maintains a spring member in a deformed state, or can change the state of an - MP0~69 I
ionization chamber or ample in e smoke detector, or the tr~nsmissivity of photoelectric cell, which in turn Jill cause a witch to convect the lusting end return meter D. A orange owe a first pressure Ply to a second pressure, Pi, the locating and source member being contacted by s connecting member which in~ulste~ them from each other at pressure Pi but permits electrical con-section Boone them it pressure Pi. For example, the I connecting member con be deformable, e.g. composed of air or other fluid insulting material.

E. A change in the intensity Dry other characteristic of electromagnetic radiation, the locating and source members being physically contacted by a connecting member which it exposed to said reedition which insulates them from each other prior to said change sod which electrically connects them to each other after said change. Suitable apparatus could for example include photoelectric cell.

F. A change in the puritan of a valve, e.g. in a refinery or other chemical process plant, thus changing the putdown of witch in a connecting member between the looting end source members.

(4? THE LIKEN, SOURCE AND RERUN MEMBERS

the locating member is preferably an elongate member, this term being used to denote member having 8 length which it ~ubst3ntially greater, e.g. at least 100 times greater, often it lest 1,000 times greater, sometimes it Lotte 10~000 times greater or even et least 100,000 time greater, than either of its other dimensions.

'122~;2~

However, the locating member con also be in the form of a sheet or eye other more complex shape.

The source member preferably ha the me general configuration and follows the eye general path a the locating member. Thus it it preferred that the 13catiag and source member are elongate members which follow the same elongate path often (but by no means necessarily) parallel to etch other.

In many Swiss, the return member which form part 10 of the reference circuit ~180 has the some general configuration end fly the same general path as the locating member. This is preferred in one embodiment of the invention in which the source sod locating members are elongate end the return member is electric-ally connected lo the locating member at the ends thereof but it otherwise insulated therefrom; on thither hand it is not necessary in this embDdi~ent when the locating and source member follow a pith in the form of a loop Jo that the return member con be a relstivsly short member which join (via the voltage-measuring device the two ends of the locating member.
The return eyebrow Jill usually hollow the Game general path foe the return end locating member in another embodiment in which, when on event occurs, not Duly is 25. connection ode between the locating God source members, but ~180 sun electrical connection of known resistance is made between the return member and the loc~tins member at the first point or at some other point on the locating member which it further away prom on the second point.

In many cases, it is convenient for one, two or all three of the locating, return and source members to comprise simple conductors which have resistance but no reactance. The locating, return and source members can be the same or different.
In order to reduce the input voltage required to provide a con-trolled current in the test circuit, the source member can be less resistive than the locating member. On the other hand, it is convenient, for making splices between cables at intermediate points, if the locating and source members to be identical In order to ensure that the resistance of the return member it not significant in the reference circuit, the return member can be less resistive than the locating member. In addition, the source or return member can be relatively large and strong (and, there-fore, usually of low resistance, for example, less than 0.01 times the resistance of the locating member in order that the apparatus has good physical properties. Thus in one embodiment, the source and locating members are identical and are wrapped around the return member which acts as the strength member of the apparatus.
The locating member preferably has sufficient impedance to cause a voltage drop which is easily and accurately measured.
Preferably, therefore, it has a resistance of at least 0.1 ohm/ft, particularly at least 1 ohm/ft, eye., 1 to 5 ohm/foot. On the other hand, its resistance should preferably not be too high and is preferably less than 104 ohm/foot, particularly less than 102 ohm/foot, especially less than 20 ohm/foot. A key feature of the present invention is 1~2S25~

that, under the condition of operation, the impedance of the lotting eyebrow it dependent sub~t~ntielly only on thy length thereof between toe awakened point end the connection point. This is entoil because it it not

5 otherwise possible to calculate the location of the convection point from the change in voltage measured by the vDlt~ge-~esRuring device. The locating member may be of content cros~-section long its length so that its re~ifitance per unit length it constant sod the voltage change it directly proportional to the distance between the first and second point. However, this is not essential, providing that the impedance changes in known phony along the length of the member, 60 that the voltage change end the distance eon be correlated.
The most common variable affecting the resistivity (and, therefore, reaistanee) of the locating member it temperature. Many materials, and in particular copper and other metals most commonly used for electrical conductors, have 8 rotate which change with - 20 temperature to an extent which, although unimportant for many purposes, can result in unacceptable ruins of error in locating the first point under conditions in which the temperature can very substantially end unpredictably along the length of the locating member.
It is preferred, therefore, that the locating member should have a temperature deficient of impedance - (usually resistance) which averse less than D.003, particularly lest than DOW, especially less then 0;00003, per degree Centigrade over at least one 25 - 30 temperature range between -100C and +50ûC, end preferably over the temperature range 09 to Luke, especially Dyer the temperature range Do to 20û C.

~L225~5~

For a ~l~pl0 ~etsl condu~tDr, thy temperature coefficient of i~lpedanoe it the slyly Eye the tg~Dp~r~ture coefficient o f rotate, The value for opus it abut one per dog C.
Mutt Hanukkah lower temperature coefficient of resistivity 5 rye jell known sod include Cnnstantan (alto known 85 YEureka)g~Mang~nin end Cope, and others listed for example in the International Critical Tables published 1929 by Mct;raw-~ll Dick to Vol. VI, pages 156-170.

It it of course i~portnnt that the toasting, sDuroe nod return members should be sufficiently strung, and should be assembled in such a way, that thicken withstand the strews on them during in~talletiDn and use For the return member this usually prevents no problem, because it con be and preferably is securely 15 enclosed in a conventional polymeric insulating jacket.
However, electrical contact is Nasser at intermediate points ox the toasting and source members, and can be necessary it intermediate points of the return member also. this can result in problems, particularly when 20 one or Gore of the members is a wire of relatively small crsss-section. However, we have found that in deny placation of the invention, e~peciclly those in which the event is the presence of an electrolyte, on excellent combination so desired properties can be obtained through the use of locating member snd/nr a member co~pri6in~ metal Gore end on elongate Scot which electrically surrounds the core and which is composed of conductive polymer. The term "electrically surrounds it used herein to mean that oil electrical paths to the sore (intermediate the ends thereof) pass through the jacket. Normally the conductive polymer will completely surround the core, being applied for example by s melt-extrusion process; however it it also possible to wake use of jacket which has alternate insulting BectiGns end conductive section .
Jo k -22~

The term "conductive polymer" is used herein to denote a composition which comprises a polymeric component (e.g., a thermoplastic or an elastomers or a mixture of two or more such polymers and, dispersed in the polymeric component, a portico-late conductive filler (e.g., carbon black, graphite, a metal powder or two or more of these). Conductive polymers are well known and are described, together with a variety of uses for them, in for example United States Patents Nos. 2,952,761, 2,978,665, 3,243,753, 3,351,882, 3,571,777, 3,757,086, 3,793,716, 3,823,217, 3,858,144, 3,g61,029, 4,017,715, 4,072,848, 4,117,312, 4,177,446, 4,188,276, 4,237,441, 4,242,573, 4,246,468, 4,250,400, 4,255,698, 4,271,350, 4,272,471, 4,304,987, 4,309,596, 4,309,597, 4,314,230, 4,315,237, 4,317,027, 4,318,881 and 4,330,704;
J. Applied Polymer Silence 19 813-815 (1975), Klason and Cubit;
Polymer Engineering and Science 18, 649-653 (1978), Narkis et at.
The resistivity of conductive polymers usually changes with temperature at a rate well above the preferred temperature coefficient of resistivity set out above, and the PTC conductive polymers often increase in resistivity by a factor of 10 or more over a 100C range. Accordingly, it is important that in a locating member comprising a conductive polymer jacket, at all temperatures likely to be encountered, e.g., at all temperatures from 0 to 100C, each longitudinal section of the conductive polymer jacket has a resistance which is at least 100 times, I' -23- I So preferably at least 1000 times the resistance of the core of that longitudinal section. In this way (since the core and the jacket are connected in parallel), the jacket does not make any substantial contribution to the resistance of the elongate conductor, and any change in its resistance with temperature is unimportant.
The second point on the locating member must have a known location, and it is normally a fixed point. When the soys-them is designed to detect different types of events occurring independently, the second point is preferably the same fixed point for detection of the different events. In the case of an elongate locating member, the second point will normally be at one end or the other of the locating member. However, the invention includes, for example, the simultaneous or sequential use of a plurality of second points to determine the locations of a plurality of first points when a number of different events having identified a number of first points.

MP0~6g 1225~S~;
SUPPLY

he runt Rich it tr~n~itted eighteen the first on second points must be of known it end I preferably supplied by 8 controlled current source, e.g. a galvano-stat; however, a controlled voltage Ursa can be used providing that a ~urrent-me~suring device it included in the apiarist 80 that the location of the first point eon be calculated. the current may be a direct current or an alternating current of regular sinusoidal or Dither for. The current which flows between the first and second point it preferably in the range of 0.05 to 100 millismp~, particularly Owl to 10 milliamps, ego Do to 3 milliamps. The controlled current source it preferably a fixed current source or 8 current source which ran be adjusted to a desired end known value, for example in obtain improved accuracy in locating a fault which was detected at a lower current level However, it it Ahab possible to Us a Fixed voltage source, in combination with a current-meacuring device which measures the current flowing between tile first and second points. The power source is preferably - connected to the-locating member at the second point at all times and, in the absence of an event, it otherwise insulated from the locating member.

(6) THE VOL~AGE-MEASURING DEVICE

the voltage-~easur~ng device can be of any kind, and suitable device sure well known to those skilled in the art. Preferably the voltage-mea6uring device is voltmeter which ha resistance of it least Lowe Dims, ED preferably it least l megohms specially at lest lo megohms .

Mpoa6g - Lowe:;
I PMYS~CAL AND ELE~TRlCAL RELA~lnNSHIPS BETWEEN THE
LD~rD~INl5 DO THY PYRITES

A briefly indicated in the description of Figure 1, the physical and electrical relationships between the cùmpsnents of the apparatus of the invention can be widely varied. Figure 2-24 show 8 number of different arrangements which pacific example of the circuit generically illustrated in Figure 1 and of various preferred embodiments of the invention. In each of Figures 2-24~ there it power source 15, a voltage-measuring device 14, locating member 11, a source member 12 and a return member 16. The locating member it shown I resistor Buick it must hove appreciable rustiness in order for the voltage drop down it to be large enough to permit accurate location of the point 1, at which the source member it connected to the locating member The source and return member are shown a simple low rustiness conductors, which they preferably are, but the source member can have high and/or indeterminate resistance (providing that the ED power source con drive a known current between points 1 : end 2) end the return member con hove 6ubstsntial resistance, providing that it it e known resistance.
The connection E, El, En end I are Winnie pa resistor if they Form port of the text circuit, since I the invention permits these connection to be of indeterminate sod high resistance (though of course they eon be of substantially zero resistance or of substantial end known rustiness On the Dither hand, these connections ore shown a simple conductor if they form part of the reference circuit, wince the invention requires that these connection are of known, end preferably smell, resistance. In a number of the Figures, there rip shown witches, I 51 and 52 ~Z25;~5~
An otter ennui con be employed, in eddit~on to simple switches awaken 2~3'D resist~ncoe eleet~onir contact, in the eta erupt, undo en other jeans p~o~idiny a eonnectiun of known resi~tanre run be used in the reference circuit. In most of Figure 2-24, the purer source is shown 88 8 controlled current ours but in Figure 3, the power source to a battery sod the test circuit includes an Peter 154; and in Figure 4 the power source it z controlled voltage AC source sod the test oirc~it again include an ammeter 154.

Some of the different possible relationships between the components will now be enumerated, using Figures 2-24 en examples of these relstion6hips.

(1) The power source can ye pow toned neon the second point on the locating member, as illustrated in Figures . 2-7 and 12-22, or near the end of the locating member which it remote from the second point, as illustrated in Figure B-9. In most case, the power source end the voltage-meusuring device Rye positioned near to each other en illustrated on Figure 2-5 and 7-22.

I A shown for example in Figure 10~ the rJppsratus eon include one or Gore witches which my be ganged together or Jay operate independently, to provide for witching the connection between the locating member and the power source from s first ~rr3ngement in which the second point is it one end of the locating member us shown in Figure 2, to D second arrangement in which the second point it sty the opposite end of the locating member, as shown in Figure 9 9 thus mewing it possible first to measure the distance from one end the an event has token piece sod then to measure the Dayton from the other end the on event his taken place.

MP0869, -27- ~225256 (3) it it nl80 ~585i~1e for the playwright to be one on which Dennis Or thy event kiwi nut only connection eighteen the source end lotting mummer, but ~180 continue between the return sod locating embryo, A shown for example in Figures 5, 7, lo and 20. Such a system can be valuable for example in providing 8 cut-to-length apparatus. The making of the oonneotion between the looting end return member con be the direct result of the making of the connection 10 between the lotting end source members, e.g. by means of c ganged witch, or the condition which causes one Connection to be made gun also cause the other connection to be ode. The e two possibilities ore shown in Figure 5. Alternatively, the connection between the toasting member can result from the existence of a condition which it different from the condition whir effects connection between the locating end source emeries. This possibility it one in Figures 7, 19 on ED.

(4) It it at o possible, as one for example in Figure 11, for the apparatus to include one or more witches, which may ye ganged together or my operate separately, Jo that the pretty am be converted into on electrical system illustrated in Figure 12, in which (a) on electrical current is driven down the whole length of the locating member ox the power source by the return member it electrically connected I to the second point on the locating member through the voltage-measuring device, and it otherwise insulted from the locating member, on I
~LZ;~5~56 (c3 then 8 second and different type of event I onnec~ion of known impedance it ode between the loc~t.in~ eyebrow end the return eyebrow, thus creating n reference circuit which comprises a voltage- measuring device, those port of the toasting member and return member which lie between the first end second points end the connection of known impedance, the voltage-me~suring device hiving B known impedance which it very high by comparison with any unknown part of the impedance of the other component of the reference circuit.

(5) As shown for example in Figure 13~ the event con comprise the existence of particular condition at etch of c plurality of sp~ced-spart 1DCatiOn87 the connection between the locating member end the source member being made through on event-sen~itive connection member comprising a plurality of condition-sens~tive embryo which are eletricelly connected in series, which sure re6pectaYely located et each of rid spaced-part locat~Dns, and each of which is electrically conductive when said condition exits it its location and it not electrically ~onductivle when slid condition does not exist it it location.

(6) As shown for example in Figure 14, the event can .
ccmpri%e the existence of particular condition it it I~sst one of a plurality of ~psced-spsrt location6,-the connection between the toasting member and the source member being sue through an event-sen~itive connection member comprising plurality of condition-3ensitive members which ore electrically connected in parallel, ~22~Z5~

which err respectively located at etch of said spaced-part locations, end Shea of which it electrically conductive when said condition exits it its vocation end it not electrically conduct when rid condition does not exist it it location.

(7) As one for example in Figure 15, the event can comprise the existence of a first condition at a first locution an the existence of a ~ecsnd condition it a second location (which may be lmmedistely edj~cent the first location) 9 the connection between the locating member end the source member being made through sun event-sensitive member comprising (a) a fir~t-condition-sensitive member which it it the first locution end which is electrically conductive when the first condition exist it the final location and is not electrically conductive when the first condition does not exist at the first location and (b) a ~econd-condition-sen itive member which it it the second location 9 which it electrically conductive when the second condition 2G exits at the second locution end it not electrically conductive when the second condition does not exist at the equine location, and which it electrically connected in series with the fir~t-condition-sensitive member.

(B) As shown for example in Figure 16, the event con I comprise the existence of a first condition at first location or the existence no a second condition at 8 second luxation (which may be immediately adjacent the first location), the connection between the locating member and the source member being mode through on event-sen~itive member comprising (a) a fir~t-condition-sensitive member which as at the first locution end which it electrically conductive when the first condition MP0~69 ~225ZS~
exists at the first locution end it not electrically conductive when the first condition dyes not exist it the First losatiDn and by a ~econd-condition-~en~tive member which it sty the second l~catiun, which it electrically conduit when the second condition exit at the second location sod is not electrically conductive when the second condition does not exit it the second location, and which is electrically connected in parallel with the fis~t-condit~on-sensitive member.

~93 It ill sly possible, as shown for example in Figure 17, for the system to include two or more source member , which become respectively connected to the locating member when particular condition (different for etch source member) exit. In this cave the event 15 it the sxi~tence of one of those two (or more) conditions at any point long the elongate path followed by the locating end source members. The system con also include switches, e.g. as shown in Figure 17, such that it it possible to disconnect ~11 but one of the source ED members, and thus to determine which of the particular conditions exits.

- (lo) It it also pc8~ible, I shown for ample in figure 18, for the system to include at least one auxiliary source member which is connected to the 25 power source end which become connected to the source member (or to another auxiliary source member) when a particular second condition exit, the equine condition being different from the first condition which causes the Ursa member to become connected to the locating member. In this case, the svçnt it the existence, at en one or more points along the path, of a second condition which kiwi the exhaler source member to become connected to the source member, and the b20 MP0869 . -31-~22~

existence, et one or dry point along the pith, of fist edition ho KIWI the Doris end locating eyebrow 5 to become connected .

ill) It it Allah possible, a shown for example in Figure 19 end 20 for the system to include it least one auxiliary return member which is connected to the voltage-oes~uriny device and which becomes connected to the Saturn member when a second condition exifits, the second condition being different from the first condition which ceases the source and locating embryo to become connected. the return member con be connected to the end of the lccating;member which is remote from the second point ox illu6trsted in Figure 19, in which essay the event is the existence of the first condition at one or more points long the pith end the existence of the second condition at one or more point along the path, with the information provided being the locution of the final condition which it nearest to the second point. Alternatively, 98 illustrated in Figure I the I return member con become connected to the locating somber as the result of third condition.

(12) It is also possible, as shown for example in Figure 21, for the apparatus to follow sun elongate path on the form of loop ED that the return member need not follow the elongate pith but con amply join, Vim the volt~ge-measurin~ device, the WOODY ends of the toasting member.

(13) It it else possible, as shown for example in Figure 22, for a plurality of event-detecting stations (which can detect the same or different event) to be positioned at location which are remote from the by 1 MPDB69 5~5~

toasting member end to be electrically (or otherwise) connected to witches (ego e~ctromagneticolly Operated relays between the Latin end source members.

(14) It it alto possible, no shown for example in Figure 24, when event-detection is required only in 6paced-apert zone, for the locating member to comprise (o) plurality of spaced-apart elongate looting component (AYE, 114~, 114C and 114D in jig. 23), etch of which provides a series of points to which the connection eon be made end preferably has a relatively high resistance per unit length, end (b) plurality of spaced-ap~rt elongate intermediate component (AYE
1158, end 115C in ire 23) which foxily separate sod electrically connect the locating components 9 which cannot become directly connected to the source member and which preferably have 8 relatively low resistance.
. This system might be used for example when detection end location woe needed within etch of a playwright of houses separated from each other long a street, but ED not between the hues ( 15) Toe method can also be used to locate event along a branched pith as illustrated in Figure 24. However, when using such a branched 8y8tem, if the voltage-Treasuring device ooze On event at Q di~tcnce beyond 25. the irrupt broaching punt then there are often two or more possible locations for the fault. It desired, the locution eon be precisely identified by connecting the controlled current source and voltmeter to the conductors et the branch punt) (preferably via low rustiness drop lends ~natnlled it the same time as the detection system). this expedient con alto be used in unbranched systems in order to provide improved accuracy of locution ~33-issue of the en after the general vicinity Do the event has teen inducted Alternatively AC current source of different frequencies eon be o~ployed sequentially and f Lowry con be placed in the different branches Jo S that only one ranch is being tested sty en one time.

By VOLTAGE DROP VS. DISTANCE
., , _.
The relationship between the voltage drop myriad by thy vDltsge-~ea~uring device undo the distance between the first and second points will depend on the 10 yo-yo in which the apparatus is designed. When connection can be made to the locating member at any point along it length, end the locating member it of uniform impedance along its length, then the relationship will be a straight line of uniform pow as illu~trsted in Figure 25. When the event-3ensitive connection means . is discontinuous, 80 that connection to the locating member Sybil only at spaced-apart punt then the relationship will be a eerie of Taipei en shown in figure 26. when the locating member it divided into JO locating and connection zones and son be contacted at ; any point-~ithin e locating zone, as shown in Figure 23, then the relationship it as shown in Figure 27.

(9) PARTICULAR EVENT-SENSITIV~ CONNECTION MEANS

Figure 28-33 show cross-sections through apparatus of. the invention. In figures 28 end 29, the apparatus includes a source member having a metal core 121 end a conductive polymer coating 122; a locating member hiving a core 111 which is composed of a metal whose receptivity it substantially invariant with temperature and e conductive polymer coating 112; and 8 return member 16 which is composed of motel and it unrounded by a polymeric ~n~ulat~ng kowtow 161.

I So In ire I n pyrrhic insulting connecting member I hiving concave traces lies between the source and locating en no thy component sure joined tsgethe~ my on perjured end therefore 5 liquid-permeeble, undulating jacket 91. So long as there it no electrolyte around the apparatus shown in Figure 29, there it no electrical connection between the locating and ooze members. However if the apart is exposed to an electrolyte) on ionic I connection it cede Steen the locating end source emboss.

In Figure 29, member 21 lie between the locating and source member, and the components are surrounded by an insulating jacket 92. Under normal conditions, the member 21 prevents electrical contact between the locating and source member&, . but the member 21 consists of or contain a material which becomes an electrical conductor when an event occurs. For example, the member 21 can comprise an organic polymer foam which is impregnated with material which forms mobile ionic specie Yen the foam structure it dsmaged9 fur example by En event involving excessive pressure transmitted through a flexible jacket I or an event involving excessive temperature which Casey the form to melt, or an event involving the presence of chemical which can penetrate the kowtow 92 (which may be portrayed for this purpose end which resect with the foamed member. The member 21 can also be composed of a material which becomes ED conductive when it it COmpreB8ed.

Referring now to Figure 3û, this it 8 CrD~S-SeCtion through apparatus for detecting en over-temperature fault condition. Locating member if and source in ember ~35~ I 2 or 6 I

I are to strips graced pretty by insulting trips ED, defining on a I between thy rondu~torfi.
Return Burr It nod nutting bucket 161 rounding it Ore alto present. A bimetallic C-clip comprising ethyl strip 7 and 8 bear on the center portions of the troupe no 12 through insulating pad 78; under normal conditions the clip it in the open position one, but it it BY con~trlleted and arranged that if the temperature essayed p~rticulsr value, the clip closes and brings the strips 11 end 12 into electrical contact Suitable C-clips con be oDmpo~ed of e spring - steel member and a memory metal member. For example, if under normal countdowns; the inner member 7 to composed of spring steel 9 end the outer member B is 15 composed of a memory metal in the marten~itic phase end it maintained in an expanded configuration by the member 7, then if the temperature reaches the trsnsfor-ration temperature of the memory metal, the member B
Jill recover, overcoming the elastic rustiness of the member 7 and bringing the strip no 12 into contact.

Figure 31 it somewhat similar to Figure ED, but make U88 of b~me~llic member to bring a strip 12 sod 8 wire 11 into electrical contact if the temperature f8118 below a preschooler level. Strip 12 it connected to C-cl~p having an inner member 7 composed of spring steel on outer member 8 composed of 3 memory ~etsl.
the Kelp it separated from wire 11 by an sir gap 21 in an aperture insulting member 20. Under normal conditiDns9 the Emory petal member 8 it in the eighteen-ED tic state end Montanans the spring steel member 7 incompre~sed configuration 80 that there 8 no c~ntsct between strip 12 and wit no 11. If the temperature S~rClp8 below the trsn~for~atiDn temperature of the memory MP~B69 _36-~225~5~

eye hut converting the member into the weak ~erten~sc tote the spring await eyebrow oxp~nd~
end equity electrical ~nn~ctio~ button the trip 12 nod the wiry 11.

In Figures 30 no 31, the member will generally Cooper a plurality of discrete, sp~ced~p~rt, members However, 8 ~nti~uou~ Member Jill also be satisf~tory.

figures 32 sod 33 show apart for detecting en increase in pressure, for example for placing under a 10 floor covering us burglar lam The source member - 12 it in the form ox- e metal trip end is surrounded by on insulating polymeric sheet 22 which has portray 21 in itfi top surface. the locating member if it a constant resistance metal wire which it separated from the member 12 by insulting sheet 22 end crosses over the portray 21. The return member 16 it placed below the second conductor end it insulted therefrom at 811 points. A flexible insulating polymeric jacket 92 surrounds the vsriou~ component. Under normal I conditions the locating end source members sure not - electrically connected. However, if the pressure on the top surface D f the insulting jacket incrP~ses ~ufficiently9 the locating member I forced through aperture 21 to contact the source member.

I The invention it illustrated by the following Examples:

MP0~69 22~ii25 eta one in figure 2 was prepared. The controller current source eye a gslvanostet Thea a oompli~nce voltage of lo volt end produced e controlled current of 0.001 imp. The voltmeter had an input l~peda~ce of 1 ego and full scale reading of 200 my the Ursa ember was a 3û A copper wire which way surrounded by a ~elt-extruded jacket of conductive polymer condition the kowtow was about 0.04 inch thick. ho conductive polymer ccmpo~ition ho resistivity of about 3 ohm.cm sty 25C end comprised carbon black (about I pretty by weight) dispersed in thermoplastic rubber which it told under the trade name PRY end which it believed to be 9 blend Do polyp propylene and an ethylene/propylene rubber stout 55 parts by weight). The locating member was the me a the firs except that 30 AWN C~nstanten wire way used instead ox the copper wire. The resistance of the .
second conductor was 2.940 ohms foot The return member Wow 12 AWN copper wire end it Wow 8UrrDUnded by polymeric insulating jacket.

In a number of tots a damp sponge we placed on toe locate and Doris member lo effect elect-rival connection between them, the member being dried between the tests. It was found that, as expected from theory, the distance (d) in feet to the damp ~p3nge could be c~lculsted from the equation V
d = 0.001 x I

where Y I top voltage (in volt) recorded by the ED voltmeter. The discrepancy between the actual end cslculsted value Do d we let than D. lo .

or k . .

~5Z5~;

R trait one in figure 2 wow prepared) using a gelv~nDatat and voltmeter pa specified in example l.
An apparatus somewhat similar in operation to that shown in Figure 33 sod 34 WAS prepared us fulled.
To provide the source member, a strip of copper foil way tuck to the interior bottom surface of a tube of Roy inked palyvinylidene fluoride. To provide the tying umber, 30 AWN ConstQntan wire aye secured to the interior top surface of the polyvinylidene fluoride tube, diametrically opposite the copper strip 3 the wire being woven through the tube at interval ED the it was maintained substantially in contact with the tube throughput its length. The return member Way a 30 AGO insulated topper wire.

In a number of sty pressure way exerted on the top surface Do the tube it a location separated from the near end. the tube deformed elastically, bringing the locating and source members Pinto contact, and resulting in a reading on the voltmeter from which the location of the pressure point elude be calculated.

Claims (45)

We claim:

1. A method for monitoring for the occurrence of an event, and for detecting and obtaining information about the event upon its occurrence, which method comprises providing a system in which, upon occurrence of the event, (1) electrical connection is made between an electrically conductive locating member and an electrically conductive source member;

the connection to the locating member being effective at a first point whose location is defined by at least one characteristic of the event;

the making of the connection enabling the formation of a test circuit which comprises (a) the connection, (b) that part of the locating member which lies between the first point and a second point having known locating on the locating member, and (c) a power source e which causes an electrical current of known size to be transmitted between the first and second points on the locating member; and the current and the locating member being such that, by measuring the voltage drop between the first and second points, the spatial relationship between the first and second points can be determined;

(2) the voltage drop between the first and second points is measured; and (3) information concerning the event is obtained from the measurement made in step (2).

2. A method according to claim 1 wherein (a) the locating member and the source member are elongate; and (b) the second point is fixed point at one end of the locating member.

3. A method according to claim 1 wherein the power source is controlled current source which delivers a known fixed current.

4. A method according to claim 3 wherein the controlled current source supplies known current within the range of 0.05 to 10 milliamps.

5. A method according to claim 1 wherein the voltage drop between the first and second points is determined by means of a voltage-measuring device which forms part of a reference circuit, the reference circuit comprising (a) the voltage-measuring device, (b) that part of the locating member which lies between the first and second points, and (c) an electrically conductive return member which (i) is electrically connected to the locating member at the second point and at another point on the locating member whose distance from the second point is at least as great as the distance from the second point to the first point, both distances being measured along the locating member, and (ii) is otherwise insulated from the locating member, the voltage-measuring device having an impedance which is very high by comparison with any unknown part of the impedance of the other components of the reference circuit.

6. A method according to claim 5 wherein the voltage-measuring device has a very high impedance by comparison with the other components of the reference circuit.

7. A method according to claim 5 wherein the return member is electrically connected to the locating member at the ends thereof and is otherwise insulated therefrom.

8. A method according to claim 5 wherein, when the event occurs, an electrical connection of known resist-ance is made between the return member and a point on the locating member whose distance from the second point is at least great as the distance from the second point to the first point, both distances being measured along the locating member, thus enabling formation of the reference circuit.

9. A method according to claim 5 wherein, when the event occurs, an electrical connection of known resistance, is made between the return member and an auxiliary return member, thus enabling formation of the reference circuit.

10. A method according to claim 9 wherein the return member is connected to the end of the locating member opposite the first point and is otherwise insulated from the locating member.

11. A method according to claim 5 which also comprises switching the components of the system from a first arrangement in which the second point is at one end of the locating member to a second arrangement in which the second point is at the opposite end of the locating member.

12. A method according to claim 5 which also comprises switching the connections between the locating member and the power source and between the locating member and the voltage-measuring device to create an electrical system in which (a) an electrical current is driven down the whole length of the locating member by the power source, (b) the return member is electrically connected to the second point on the locating member through the voltage-measuring device, and is otherwise insulated from the locating member, and (c) when a second and different type of event occurs, a connection of known impedance is made between the locating member and the return member, thus cresting a reference circuit which comprises a voltage- measuring device, those points, of the locating member and return member which lie between the first and second points, and the connection of known impedance, the voltage-measuring device having a known impedance which is very high by comparison with any unknown part of the impedance of the other components of the reference circuit.

13. A method according to claim 1 wherein the connection between the locating member and the source member has a substantial and unknown impedance.

14. A method according to claim 1 wherein the connection between the locating member and the source member comprises an ionic connection.

15. A method according to claim 1 wherein (a) the locating member and the source member are elongate;

(b) the second point is at one end of the locating member;

(c) one end of an electrically conductive return member is electrically connected to the second point on the locating member, and the other end of the return member is electric-ally connected to the other end of the locating member through a voltage-measuring device, the locating member and the return member being otherwise insulated from each other;

(d) the voltage-measuring device has a known impedance which is very high by comparison with the impedance of the locating member and the return member and the electrical connect-ions between them; and (e) the source member is electrically connected to the locating member and to a controlled current source so that a current of known fixed size flows through the locating member between the first and second points.

16. A method according to claim 1 wherein the event takes place adjacent the first point and the infor-mation obtained compreses the location of the event.

17. A method according to claim 1 wherein the event takes place at a location remote from the first point and identifies the first point via an electrical connection means, and the information obtained comprises the location of the event.

18. A method according to claim 1 wherein the locating member comprises a plurality of spaced apart locating zones, each of said zones providing a series of points to which the connection can be made, and a plurality of spaced-apart connection zones which physically separate and electrically connect the locating zones and which cannot become connected to the source member.

19. A method according to claim 1 wherein the locating member comprises a wire having a resistance of at least 1 ohm/foot.

20. A method according to claim 1 wherein the locating member has a temperature coefficient of impedance which averages less than 0.003 per deg C over the temperature range 0 to 100°C.

21. A method according to claim 1 wherein the locating member comprises (A) an elongate core which is composed of a metal whose temperature coefficient of resistivity averages less than 0.003 per deg C over the temperature range 0° to 100°C and in which each longitudinal section has a resistance from 10-4 to 104 ohms/foot; and (B) an elongate jacket which is composed of a conductive polymer, which electrically surrounds the core and in which each longitud-inal section has a resestance which is at least 100 times the resistance of the core of that longitudinal section at all temperatures from 0°to 100°C .

22. A method according to claim 21 wherein the metal has a temperature coefficient of resistivity of less than 0.0003 per deg C over the temperature range 0° to 100°C.

23. A method according to claim 1 wherein at least a part of at least one of the locating member and the source member comprise an elongate metal core which is electrically surrounded by an elongate jacket which is composed of a conductive polymer, and the event is the presence of sufficient electrolyte to connect the locating and source members.

24. A method according to claim 1 wherein the event is a change from a first temperature, T1 to a second temperature, T2, and wherein the locating and source members are physically contacted by a connecting member which insulates them from each other at T1, and which electrically connects them at T2.

25. A method according to claim 1 wherein the event is a change in the concentration of a particular substance, and the locating and source members are physically contacted by a connecting member which insulates them from each other prior to said change and which effects or permits electrical connection between the locating member and the source member as a result of said change.

26. A method according to claim 1 wherein the event is a change from a first pressure, P1, to a second pressure, P2, and the locating and source members are contacted by a connecting member which insulates them from each other at pressure P1 but which effects or permits electrical connection between the locating and source members at pressure P2.

27. A method according to claim 1 wherein the event is a change in electromagnetic radiation, and the locating and source members are physically contacted by a connecting member which is exposed to said radiation, which insulates the locating and source members from each other when the electromagnetic radiation prior to said change and which electrically connects them as a result of said change.

28. A method according to claim 1 wherein the locating and source members are separated from each other by a deformable insulating medium, and when an event takes place, at least one of the locating and source members changes shape, thus deforming the insulating medium and effecting electrical contact between the locating and source members.

29. A method according to claim 1 wherein the event comprises the existence of a particular condition at each of a plurality of spaced-apart locations, and the connection between the locating member and the source member is made through an event-sensitive connection member comprising a plurality of condition-sensitive members which are electrically connected in series, which are respectively located at each of said spaced-apart locations, and each of which is electrically -47- .

conductive when said condition exists at its location and is not electrically conductive when said condition does not exist at its location.

30. A method according to claim 1 wherein event-monitoring is required only in spaced-apart zones, and the locating member comprises (a) a plurality of apaced-apart locating components which are in said zones and to which connection is made upon occurrence of an event, and (b) a plurality of spaced-apart intermediate components which physically separate and electrically connect the locating components and which cannot become directly connected to the source member.

31. A method according to claim 1 wherein the event comprises the existence of a first condition at a first location and the existence of a second condition at a second location, end the connection between the locating member and the source member is made through an event-sensitive member comprising (a) a first-condition-sensitive member which is at the first location and which is electrically conductive when the first condition exists at the first location and is not electrically conductive when the first condition does not exist at the first location and (b) a second-condition-sensitive member which is at the second location, which is electrically conductive when the second condition exists at the first location and is not electrically conductive when the second condition does not exist at the second location, and which is electrically connected in series with the first-condition-sensitive member.

32. A method according to claim 1 wherein the event comprises the existence of a first condition at a first location or the existence of a second condition at a second location, and the connection between the locating member and the source member is made through an event-sensitive member comprising (a) a first-condition-sensitive member which is at the first location and which is electrically conductive when the first condition exists at the first location and is not electrically conductive when the first condition does not exist at the first location and (b) a second-condition-sensitive member which is at the second location, which is electrically conductive when the second condition exists at the first location and is not electrically conductive when the second condition does not exist at the second location, and which is electrically connected in parallel with the first-condition-sensitive member.

33. A method according to claim 1 wherein the event comprises the existence of a first condition which causes the source member to become connected to the locating member and the existence of a second condition which causes a second electrical connection to by made between the locating member and an auxiliary locating member, the second connection forming part of the test circuit.

34. Apparatus for detecting and obtaining information about an event, which apparatus comprises (1) an elongate electrically conductive locating member whose impedance from one end to any point on the locating member defines the spatial relation ship between that end and that point;

(2) an elongate electrically conductive source member;

(3) an event-sensitive connection means which, upon occurrence of an event, effects electrical connection between the locating member and the source member, the connection being effective at a first point on the locating member which is defined by at least one characteristic of the event;

(4) a voltage-measuring device for determining the voltage drop between the first point and a second point which is at one end of the locating member; and (5) a power source which is electrically connected to the second point on the locating member and, in the absence of an event, is not otherwise connected to the locating member, so that, when occurrence of an event causes an electrical connection to be made between the locating and source members, this enables the formation of a test circuit which comprises (a) the connection, (b) that part of the locating member which lies between the first and second points, and (c) the power source, and in which test circuit a current of known size is transmitted between the first and second points on the locating member.

35. Apparatus according to claim 34 wherein the power source is a controlled current source which, when an event takes place, supplies a known fixed current.

36. Apparatus according to claim 34 wherein, when an event takes place, the voltage-measuring device forms part of a reference circuit which comprises (a) the voltage-measuring device, (b) that part of the locating member which lies between the first and second points, and (c) an electrically conductive return member which (i) is electrically connected to the locating member at the second point and at another point on the locating member whose distance from the second point is at least as great as the distance from the second point to the first point, both distances being measured along the locating member, and (ii) is otherwise insulated from the locating member, the voltage-measuring device having an impedance which is very high by comparison with the impedance of the other components of the reference circuit.

37. Apparatus according to claim 34 which further comprises (6) an electrically conductive return member having a first end which is electrically connected to one end of the locating member via the voltage-measuring device and a second end which is electrically connected to the other end of the locating member, the return member being otherwise insulated from the locating member.

38. Apparatus according to claim 34 which further comprises (&) an electrically conductive return member, having a first end which is electrically connected, via the voltage-measuring device to the second point on the locating member, the return member, in the absence of an event, being otherwise insulated from the locating member; and (7) a second event-sensitive connection means which, when an event takes place, effects an electrical connection of known resistance between the return member and a point on the locating member whose distance from the second point is at least great as the distance from the second point to the first point, both distances being measured along the locating member.

39. Apparatus according to claim 38 which further comprises means for switching the connections between the components of the system from a first arrangement in which the second point is at one end of the locating member to a second arrangement in which the second point is at the opposite end of the locating member.

40. Apparatus according to claim 38 which further comprises means for switching the connections between the locating member and the power source and between the locating member and the voltage-measuring device to create an electrical system in which (a) an electrical current is driven down the whole length of the locating member by the power source, (b) the return member is electrically connected to the second point on the locating member through the voltage-measuring device, and is otherwise insulated from the locating member, and (c) when a second and different type of event occurs, a connection of known impedance is made between the locating member and the return member, thus creating a reference circuit which comprises a voltage- measuring device, those parts of the locating member and return member which lie between the first and second points, and the connection of known impedance, the voltage-measuring device having a known impedance which is very high by comparison with any unknown part of the impedance of the other components of the reference circuit.

41. Apparatus according to claim 34 wherein the event-sensitive connection means is physically adjacent the first point.

42. Apparatus according to claim 34 wherein the event-sensitive connection means comprises an event-sensitive part which is physically remote from the first point, and a connection part which is electrically connected to the event-sensitive part and is physically adjacent the first point.

43. Apparatus according to claim 34 wherein the locating member comprises a plurality of spaced-apart locating zones, each of said zones providing a series of points to which the connection can be made, and a plurality of spaced-apart connection zones which physically separate and electrically connect the locating zones and which cannot become connected to the source member.

44. Apparatus according to claim 34 wherein the locating member comprises a wire having a resistance of at least 1 ohm/foot.

45. Apparatus according to claim 34 wherein the locating member has an average temperature coefficient of impedance of less than 0.003 per deg Centigrade over at least one 25°C temperature range between -100°C and +500 C.