AU602185B2 - Apparatus for detecting and obtaining information about changes in variables - Google Patents

Description

Form Form COMMONWEALTH OF AUSTRALIA PATENTS ACT 1952 COMPLETE SPECIFICATION

(ORIGINAL)

FOR OFFICE USE t t t Short Title: Int. Cl: Application Number: Lodged: Complete Specification-Lodged: Accepted: Lapsed: Published: Priority: tis af t'Utsi T rnr X L ['tioli ahd i t priating.

Related Art: TO BE COMPLETED BY APPLICANT Name of Applicant: Address of Applicant: Actual Inventor: Address for Service: RAYCHEM CORPORATION 300 Constitution Drive, Menlo Park, California 94025, U.S.A.

Peter Leonard Brooks Thomas Winton Tolles, Michael Masia, James Patrick Reed and Larry Russell Reeder GRIFFITH HASSEL FRAZER 71 YORK STREET SYDNEY NSW 2000

AUSTRALIA

Complete Specification for the invention entitled: APPARATUS FOR DETECTING AND OBTAINING INFORMATION ABOUT CHANGES IN VARIABLES The following statement is a full description of tl is invention, including the best method of performing it known to me/us:- 8066A/ls MP0869 METHOD FOR DETECTING AND OBTAINING INFORMATION ABOUT CHANGES IN VARIABLES This invention relates to methods and apparatus for detecting and obtaining information about (particularly locating) changes in variables.

A number of methods have been proposed for detecting o and locating changes in variables along an elongate o path, e.g. the occurrence of a leak (of water or another liquid or gas), insufficient or excessive 10 pressure, too high or too low a temperature, the presence or absence of light or another form of electromagnetic radiation, or a change in the physical position 0 of a movable member, e.g. a valve in a chemical process plant or a window in a building fitted with a burglar o o o" 15 alarm system. Changes of this kind are referred to in this specification by the generic term "event".

Reference may be made for example to U. S. Patents Nos.

1,084,910, 2,581,213, 3,248,646, 3,384,493, 3,800,216, and 3,991,413, U.K. Patent No. 1,481,850 and German Offenlegungschriften Nos. 3,001,150.0 and 3,225,742.

However, the known methods are expensive, and/or inaccurate, and/or cannot be used when the event causes electrical connection between two conductors through a connection which is of high or indeterminate resistance, e.g. an ionically conductive connecting element.

We have now discovered a simple and accurate method and apparatus for monitoring for the occurrence 1 i-2- MP0869 of an event, and for detecting and obtaining information about the event upon its occurrence as soon as it occurs or at some time after it has occurred). In this method, upon occurrence of the-event, at least one electrical connection is made between a source member and a locating member of known impedance characteristics, the connection or connections being effective at a first point at which the event takes place (or whose o lscation is defined by some other characteristic of the S 10 event). A current of known size is then driven through 0o the electrical connection(s) and down the locating an imember to a second point whose location is known. The voltage drop between the first and second points is I then measured and the location of the first point can then be determined.

ooo When the occurrence of the event causes a single 00 oor very short connection to be made between the locating !I member and the source member, then the "first point" 0will be easily identified, since it is the only connection point. However, when the event results in connection at two or more spaced-apart locations and/or over a I 0 0 finite lenth of the locating member, the "first point", i.e. the point whose location is determined from the measured voltage drop, is some intermediate point (which, if there are connections at two or more k spaced-apart locations, may be at a location at which there is no connection between the locating and source members). It is for this reason that the connection to the locating member is referred to herein as being "effective" at the first point.

The invention described in parent aipplication no.

i :30002/84 incorporated here by reference overcomes one or ii j more of the disadvantages of the known processes. For many i uses, a particularly important advantage is that the information obtained can be independent of the irpedance of the connection to the locating member, i.e. the information obtained remains the same even if a substantial and unknown change is made in the impedance of the connection.

In one aspect, the invention, described in the parent 10 application no, 30002/84, provides 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, i electrical connection is made between a locating o r member and a source member; j{ the locating member and/or the source member comprising a metal core and an elongate jacket which electrically surrounds the ,:ore and which is composed of a i conductive polymer; i the connection to the locating member being effective i 25 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 the connection, (b) that part of the locating member which lies between the first point and a second point having a known location on the locating member, and a power source which causes an electrical current of known size to be transmitted between the first and second points on the locating member; and 5788S/Is -3the current and the locating member being such that, by measuring the voltage drop between the first and second points, the spatial relationship between the fi~:t and second points can be determined; the voltage drop between the first and second points is measured; and information concerning the event is obtained from the measurement made in step ,T In one aspect the present invencion provides novel elongate articles which can be used as the locating member 4o4 (and optionally also as the source member) in the method and 0 0 t 15 apparatus of the invention, in particular articles which o0 comprise oSo an elongate core which is composed of a metal whose temperature coefficient of resistivity averages ,0 less than 0.003 per degree Centigrade over the 20 temperature range 00 to 100°C and in which each oo, longitudinal section has a resistance which is from 10 4 to 10 4 ohms/foot, and 400Qoa an elongate jacket which is composed of a conductive polymer which electrically surrounds the core, and in which each longitudinal section has a a000 resistance which is at least 100 times the resistance o 4S: of the core of that longitudinal section at all temperatures from 0° to 100 0

C.

In a second aspect the present invention provides an event-sensitive module which is suitable for use as a component in a method described above, the module comprising a first impedant component having substantial impedance; a first conductor which has a relatively very small impedance and one end of which is connected to the first impedant component; a second impedant component having the same impedance as the first impedant component; 5788S/1s -4a second conductor which has a relatively very small impedance and one end of which is connected to the second impedant component; the first impedant component and the first conductor, in the absence of an event, being electrically insulated from the second conductor and the second impedant component; and an even,:-sensitive connection means which, upon occurrence of an event, can effect electrical connection between the first and second conductors; S the first impedant component and the first conductor being connectable in series with incoming and outgoing portions of 0t intermediate components of an elongate locating member, and 15 the second impedant component and the second conductor being 0o00 connectable in series with incoming and outgoing portions of 0 "oo intermediate components of an elongate source member.

BRTEF DESCRIPTION OF THE DRAWING The invention is illustrated in the accompanying 0 20 drawing, in which °o.

1 o Figure 1 is a generalized schematic circuit diagram of the method of the invention described in the parent 404944 application no. 30002/84, Figure 2 is a schematic circuit diagram of the method and apparatus of the invention, Figures 3-6 are diagrammatic cross-sections through Sapparatus of the invention, DETAILED DESCRIPTION OF THE INVENTION In the interest of clarity, the following detailed description of the invention includes sections which are 4 chiefly or exclusively concerned with a particular part of the invention. t: is to be understood, however, that the relationship between different parts of the invention is of significant importance, and the following detailed description should be read in the light of that understanding and in the light of the parent application no.

30002/84 incorporated herein by reference, it should also be understood that, where features of the invention are 5788S/ls *Wr I

I

described in the context of particular Figures of the drawing, the same description can also be applied to the invention in general and to the other Figures, insofar as the context permits.

1. THE ELECTRICAL CHARACTERISTICS OF THE INVENTION The basic electrical characteristics of the invention can best be understood by reference to Figure 1, which schematically represents a substantial number of the preferred methods and apparatus of the invention. In Figure 1, there is an elongate locating member 11, an elongate source member 12, a voltage-measuring device 14, a power Ssource 15 and an elongate return mem.)er 16. The source member is electrically S S i 5788S/ls 4 MP0869 o 0 q 0 0 00 as 0 00 0 0 0 o 0 0 0 D 0 *o O0 0 00 I t connected, through the power source, to one end of the locating member; in the absence of an event, there is no other electrical connection between the locating member and the source member. Between the source and locating members (but not shown in Figure 1) is an event-sensitive connection means (this term being used to include a continuous event-sensitive connection means and a plurality of spaced-apart event-sensitive connection means) which becomes conductive at any 10 location at which an event takes place. In Figure 1, an event has taken place at a first point 1 which lies somewhere on the locating member, but whose location is otherwise unknown. As a result of the event, an electrical connection E has been made between the 15 locating and source members. The power source 15 is connected via connection means 152 to the locating member at one end thereof, designated by the numeral 2, which is the "second point" in the definitions given above of the method and apparatus of the invention.

(The second point could be at any point of known location between the end of locating member 11 and the connection point 1, providing that the voltage-measuring devi.ce is arranged to measure the voltage drop between the first and second points.) The power source is also connected to the source member by an auxiliary connection member 13; as schematically indicated by the plurality of connections 151, the connection between the power source and the source member can be made at any one or more points on the source member. Furthermore, these connections can be of any and unknown impedance, providing the power source can drive a known current between the first and second points of the'locating member. Thus the making of the connection at point I ti I MP0869 results in the formation of a test circuit which Sincludes the connection, the locating member between points 1 and 2, the power source 15, the auxiliary connection member 13, and (unless a single connection 151 is made bLtween the power source and the source member at the connection point) part of the source member 12. As will be further discussed below, important advantages can be obtained if the only variable in the impedance of the test circuit is the impedance of the connection between the source and locating members.

i This result can be achieved by making use of a source ii member which has the same impedance characteristics as the locating member, and an auxiliary member which is connected to the source member only at the end thereof which is remote from point 2.

i The voltage-measuring device is connected to the i second point 2 on the locating member (via the return Smember 16) and is also connected to the locating member at one or more points whose distance from the second point is at least as far as the first point 1; as l schematically indicated by the plurality of connections 141, these connections must be of known impedance or an Simpedance which is very small by comparison with the I impedance )f the voltage- isuring device. Thus the voltage-measuring device forms part of a reference 'y circuit which comprises the device 14, at least that P part of the locating member 11 between points 1 and 2, and the return member 16.

The power source 15 and the voltage-measuring device 14 can be connected to the point 2 qn the locating member 11 in any convenient way. Thus, as MP0869 indicated by the plurality of connections 153, the connection member 152 and the return member 16 can be connected to each other at any one or more locations.

it will be seen that the location of point 1 can be calculated if the following are known:the current flowing between points 1 and 2, V(b) the impedance of the components of the reference circuit, the voltage drop measured by the voltagemeasur~ing device, the location of point 2, and th-, impedance of the locating member between 4, 01 point 2 and each point on the locating member.

Systems in which these features are known can be provided int a number of different ways. The accuracy with -which the first point can be located is limited by the ratio of the impedance of the voltage-measuring device to any unknown part of the impedance of the other components of the reference circuit, and in most cases it, Is convenient to use components such that the ratio of the impedance of the device to the total impedance of the rest of the reference circuit Is very high. Accordingly, these ratios should preferably be at least 100, particularly at least 1,000, especially at least 10,000. It is for these reasons that the connections 141 and 153 in F'igure 1 are shown as having low resistance. By contrast, the impedance of the connection between the locating and Source membeest and the impedance of the other components of thle test circuit, do not affect the accutacy of the Itormation, obtatned; this, Ls an important advantage of the Invention, MP0869 2. INFORMATION WHICH CAN BE PROVIDED A8OUT AN EVENT The method of the invention not only detects that a particular event has taken place, but also provides information about the event. In many cases, the information provided about the event is its location, particularly when the event takes place at (or near) the location of the first point. However, the information provided can be other information; for example when the temperature at a particular location is being monitored, one point on the locating member can be identified when the tomperatuue is in one temperature range and another point can be identified when the temperature is in a different temperature range. As just noted, the location of the event may be at, or close to, the first point on the locating member.

However, this is not necessarily so; for example, one or more remote event-detecting stations can be connected, electrically or otherwise, to different points on a central locating member, the locations of the connection points being characteristic of the locations of the event-detecting stations. The method of the invention will provide some, but not necessarily all, the desired information about the event. For example, the method can usefully be employed to determine that a given event. the opening of a. valve) has taken place at one or more of a relatively small number of different locations, 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 and different method of the invention) to determine precisely where the event has taken place.

41-MPQO69 ji3. EVENTS WHICH CAN BE DETECTED, AND EVENT-SENSITIVE- CONNECTION MEANS3 F'OR DETECTING THEM The event which is detected in the method of the invention can be an event which i's not desired (a fault) or an event which is desired. The evont can be the existence of a particular condition or a change in a single variable, e.g. an increase In pressure above a particular value, or a simnultaneous or sequential change in two or more varlablas, An increase in pressure accompanied by an increase in tem~perature, 1 The event can be a change in a variable which~ lasts for only a very short time, or a change in a variabl.e which is maintained for some minimum time. The event can be of any kind which directly or indirectly 'i~nts or causes the current to be transomitted between the first point and the second point on the locating mnibeir. As noted above, the information obtained Is independent of the impedance of the connection. Thus the connection between the locating and source members can be of any' kind$ for example an electronic connection (w vw be of substantially zero impedance or can have nta impedance), or an ionic connection resulting from thi6 presence of~ an electrolyte, or~ an inductive conneot}ont The change which take's pla~ce in order, to effect the connection between the locating and source conductors is preferably a reversible change. However, the invention Is also useful when the change is a permanent one# so that the apparatus must be replacod or repaired before the system is Operat1.onal Again. The 0YtO10 cqin be arranged so that it signals an event only while the event Is taking place or gio that It sign~ls Lhat an event has occurred i.n the past; In the latter ease, the system will normally be arrcinged so that it tan be reset.

-12--MP0869 Examples of events which can be detected include, but are not limited to, the following.

A. The presence of water or another electrolyte which provides an ionic connection between exposed surfaces of the locating and source members, especially when at least part of at least one of these comprises a metal core surrounded by a conductive polymer. In this case, the event-sensitive connection means can be merely a space between the locating and source members, or it can be a connection member on which the electrolyte oil$ Scollects or which absorbs the electrolyte.

B. The existence of a temperature which is below a first temperature T 1 or above a second temperature

T

2 In~ one apparatus for detecting such a condition, the locating and source members are physically contacted by a connecting member which insulates them from each other at TIand connects them to each other at T 2 For example, at least part of the oconnecting mel'ber can comprise a first material and a second materi'al which is dispersed in the first material and which forms mobile ionic species when th-e temperature changes from T I to T 2 Thus the first material can be one which changes phase, e.g. melts, when the temperature changes from T I to T 2 In another apparatus for detecting a temperature change, the locating and source members are separated from each other by a deformable insulating medium, e.g.

an insulating medium which is at least In part a fluid, e.g. air, and the apparat comprises a (-Qnnecting member which changes shape when the tempecature changes from T I to T 2 thus forcing the members into -13- MP0869 contact, by deforming the insulating medium, or, if the connecting membeL is itself conductive, by forcing the connecting member through the insulating medium to connect the members. The connecting member can comprise a heat-recoverable polymer or a heat-recoverable memory 4 t4 LI #0 O 4 o t*t 0 04 o 4 4444 0444 0 00+0 004614 o i o 04 00 4 o ot o 00 0 4.4 4 COp, 40 0 4 oetI4~ 4 4, 4 0. t metal or can comprise a bimetallic strip. The term "1memory metal" is used herein to denote one of the metal alloys (in particular various brass alloys and nickel-titanium alloys) which exist in a strong austen- 10 itic state abov~e a transformation temperature and in a weak martensitic state below that transformation temperature, and which, if fabricated in a first shape in the austenitic state, can be cooled to the martensitic state and then deformed, will retain the deformed 15 configuration until reheated to the austenitic state, when they will revert (or attempt to revert) towards the original shape. W~here 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 sooirce members either whien the temperature rises above the transformation temperature 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 comprising them, reference may be made for example to U.S. 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, the disclosures of which are incorporated herein by reference.

C.I A change in the concentration of a particular substance, which may for example be a gas, a liquid ov a solid dispersed in a gas or a liquid, the locating -14- MP0869 and source,- members being physically 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 c-an 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. Alter.natively, 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 svbstance 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 ionization chamber, for example in a smoke detector, or the transmissivity of a photoelectric cell, which in turn will cause a switch to (4-;nnect the locating and return members.

D. 4, change from a first pressure Pit to a second presswire, P 2 r the locating and source members being contacted by a connecting member which insulates them from each other at pressure P 1 but permits electrical connection between them at pressure P 2 For example, the connecting membe.-r can be deformable, e.g. composed of air or other fluid, insulating material.

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

V S 1 MP0869 a a o 0 o ooo 0 04 O 00 00 t 00 00 6Q 0a 0 6 0d o '20 0 00 0 0t 0 0 00b F. A chango in the position of a valve, e.g. in a refinery or other chemical process plant, thus changing the position of a switch in a connecting member between the locating and source members.

SETTING A MAXIMUM FOR THE IMPEDANCE OF THE CONNECTION BETWEEN THE SOURCE AND LOCATING MEMBERS In some situations, it is desirable that the system should not signal an event when the connection between the source and locating members has an impedance over some preselected value, for example when the presence 10 of a small amount of electrolyte makes a very high resistance connection. In these situations, the system is preferably such that when the current in the test circuit is below a preselected value, the occurrence of an event is not signalled.

15 This is particularly important when, as is preferred, the power source is a fixed current source, since the voltmeter may otherwise provide a false indication of the location of the event. This is because the fixed current source will only provide the expected fixed current if the compliance voltage of the power source is high enough to drive the fixed current through the test circuit. Therefore, if the impedance of the test circuit is too high, the actual current in the test circuit will be less than the "fixed" current, and the voltage drop between the first and second points on the locating member will not correctly represent the location of the first point.

-16- MP0869 actual current in the test circuit will be less than the "fixed" current, arid the voltage drop between the first and second points on the locating member will not correctly represent the location of the first point.

This difficulty can be avoided by blanking out the display on (or associated with) the voltmeter if the Ott acurrent is below the fixed value or by including in the 0 test circuit a current switch which will prevent 0 9 0 040currents below the "fixed" current from flowing in the 00010 test circuit.

6 4, 000 Even when the information provided about the event is correct, delivery of that information may be undesir- 0 0 000able. Under these circumstances, when using a constant 0 00 current source, the output voltage of the source can be monitored, and delivery of information prevented unless 00 -04ithe output voltage is within a predetermined range.

0 4 Similarly, when using a constant voltage source, the current in the test circuit can be monitored, and delivery of informaltion prevented (for example by use of a current switch or by blanking out the display on, or associated with, the voltmeter) unless the current *1 is within a predetermined range.

in a system of this kind, the critical parameter (in determining whether or not the information is delivered) io the imvpedance of the test circuit, and it is, therefore, desirable that the only variable impedance in the, test circuit should be the Lmpedance of the connection. This can be achieved by including in the test circuit a component which is connected in secries with that part of the locating member which lies between the first and second points, and has an impedance substantially equal to the difference between 5788S/3.s -B o -17- MP0869 the total impedance of the locating member and the impedance of that part of the locating member which lies between the first and second points. Such a component is preferably provided by making use of a source member which has the same impedance characteristics as the locating member, and by ensuring that the test circuit includes complementary portions of the source and locating members which, taken together, have the same impedance wherever the connection is made. Thjs can be done by making the return member form part of the test circuit (as shown in o4° Figure or by including an auxiliary member which is connected to the end of the source member which is Soo remote from the second point. If such a component is 15 present, the sensitivity of the system will be the same oatt throughout its length. In the absence of such a component, the impedance of the locating member (between the first and second points) will also be a variable, and it will not be possible to fix precisely the range 20 of impedances of the connection which will cause an event to be signalled. When no such component is present, the limiting value or values of the impedance of the connection should preferably be at least 2 times, particularly at least 5 times, especially at least 10 times, the impedance of the full length of the locating member.

The sensitivity of such systems can easily be changed (for example so that leaks of different minimum sizes are signalled). When using a fixed current source, sensitivity can be changed by changing the compliance voltage of the source and/or by including a known impedance in the test circuit, and/or by changing -18- MP0869 the preselected range of output voltages. When using afixed voltage source, the size of the voltage can be changed, and/or a known impedance can be included in the test circuit, and/or the preselected current value can be changed.

The invention includes apparatus which is suitable for connection to locating, source and return members in order to provide a system in which information is reported only when V/1 is within a predetermined range, the apparatus comprising a first terminal; a second terminal; a third terminal; #too(4) means for connecting the first and second terminals to a power source; a voltage-measuring device for measuring the voltage drop between the second and third terminals; a display unit for displaying information derived from a voltage drop measured by the voltage-measuring device.; and a device which, when the first and second terminals are connected to a power source and are connected to each other through a locating member and a source member, thus forming a test circuit, prevents the display unit from displaying information If the value of the ratio V/1 is outside a predetermined range, where I is the current in the te~t circuit in amps and V is the output voltage of the power source in volts.

ii o oo o 0 a 000 0 a.

00 o ooo 00 00 0 00 0000 o 0 0000 0 000000 p 0 -19- This apparatus will often comprise a support member to which components to are attached, and/or a housing which provides physical and/or electrical protection for the components.

-Ui MEASURING THE VOLTAGE DROP DOWN THE LOCATING MEMBER WITH THE AID OF A REFERENCE IMPEDANCE When a "fixed" current source is used to provide a very low current, the current may vary substantially (e.g.

by about e- from the "fixed value (even when the output voltage i less than the compliance voltage). Other factors may also cause the current in the test circuit to vary with 15 time. Under these circumstances, preferably the test circuit includes a reference impedance which is connected in series with the locating member, and the location of the first point is calculated from the ratio of the voltage drop between the first and second points to the voltage drop over the reference impedance. In effect, this procedure measures the current in the test circuit by measuring the voltage drop over the reference impedanue. For further details, reference should be made to European Application No. 85 302 559.1 (Publication No. 160,441) which includes the 25 disclosure of United States Patent Application Serial No.

603, 484, filed by Bonomi and Frank on April 21., 1984 (MP0932-USI).

0400 o 0 00*0 000* 0 00 04 0 00 00 0 000 61 THE LOCATING MEMBER The locating member is preferably an elongate member, this term being used to denote a member having a length which is substantially greater, e.g. at least 100 times greater, often at least 1,000 times greater, sometimes at least 10,000 times greater or even at least 1000000 times greater, than either of its other dimensjon$.

'NT 8012S/MS m However, the locating member can also be in the form of a sheet or some other more complex shape.

The locating member preferably has sufficient impedance to cause a voltage drop which is easily and accurately measured. Preferably, therefore, it has a resistance which averages at least 0.1 ohm/ft (0.33 ohm/rn), particularly at least 1 ohm/ft (3.3 ohm/in), e.g. 1 to ohm/foot (3.3 to 16.5 ohm/in). On the other hand, its resistance should preferably not be too high and preferably averages less tchan 10O4 ohm/foot (3.3 x 10 4 ohm/in), particularly less than 10 2ohm/foot (3.3 x 10 2ohm/in), e especially less than 20 ohm/foot (65.5 ohm/in). A key feature of the present invention is that, under the conditions of operation, the impedance of the locating £1 member is dependent substantially only on the distance between the first and second points. This is essential because it is not otherwise possible to calculate the location of the first point from the change in voltage measured by the voltage-measuring device. The locating member may be of constant cross-section along its length o 000 that its resistance per unit length is constant and thz 0 voltage change is directly proportional to the distance between the first and second points. However, this is not essential, providing ttiat the impedance changes in a k~nown fashion along the length of the member, so that, the vol~tage change and the distance can be correlated. Thus under some circumstances, consi1derable advantages may result from the use of a locating member which comprises a plurality of spaced-opart impedances which are connected by intermediate elongato components of low impedance, as described in European Appplication No. 85 302 558.3 (Publication No.

164,838) which includes the disclosure of the application f iled in 8012S/MS

-M

-21- MPO869 o 9 o 4s4 the United States by Paul Hauptly @4.

1984 (MP0920-US1). The most common variable affecting the resistivity (and, therefore, resistance) of the locating member is temperature. Many maherials, and in particular copper and other metals most commonly used for electrical conductors, have a resistivity which changes with temperature to an extent which, although unimportant for many purposes, can result in unacceptable margin3 of error in locating the first point under conditi,,ins in which the temperature can vary substantially ard unpredictably along the length of the locating member. It is preferred, therefore, that the locating member should have a temperature coefficient oE imk.edance (usually resistance) which averages less than 0.003, 15 particularly less than 0.0003, especially less than 0.00003, per degree Centigrade over at least one 250 temperature range between -100 0 C and +500C, and preferably over the temperature range 01 to 100*C, especially over the temperature range 00 to 200 0 C. For a simple metal conductor, the temperature coefficient of impedance is the same as the temperature coefficient of resistivity. The value for copper is about 0.007 per deg C. Metals having lower temperature coefficients of resistivity are well known and include Constantan (also known as Eureka), Manganin and Copel, and others listed for example in the International Critical Tables, published 1929 by McGraw-Hill Book Co., Vol.

VI, pages 156-170.

It is of course important that the locating, source and return members should be sufficiently strong, and should be assembled in such a way, that they can withstand the stresses on them during installation and t I -22- MP0869 i use. For the return member this usually presents no 'I problem, because it can be and preferably is securely enclosed in a conventional polymeric insulating jacket.

I However, electrical contact is necessary at intermediate i 5 points of the locating and source members, and can be necessary at intermediate points of the return member i also. This can result in problems, particularly when one or more of the members is a wire of relatively ismall cross-section. However, we have found that in many applications of the invention, especially those ii which the event is the presence of an electrolyte, an 4 excellent combination of desired properties can be obtained through the use of a locating member and/or a member comprising a metal core and an elongate jacket which electrically surrounds the core and which is composed of a conductive polymer. The term "electrically surrounds" is used herein to mean that all electrical paths to the core (intermediate the ends thereof) pass through the jacket. Normally the conductive polymer will completely surround the core, being applied for example by a melt-extrusion process; however it is also possible to make use of a jacket which has alternate insulating sections and conductive sections.

The term "conductive polymer" is used herein to denote a composition which comprises a polymeric component a thermoplastic or an elastomer or a mixture of two or more such polymers) and, dispersed in the polymeric component, a particulate conductive filler 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 U.S. Patents Nos.

-23- MP0869 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, 3,861,029, 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 Science 19 813-815 (1975), Klason and Kubat; Polymer Engineering and Science 18, 649-65? (1978), Narkis et al; German OLS 2,634,999; 2,755,077; 2,746,602; 2,755,076; 2,821,799; European Application NO. 38,718; 38,715, 38,718, 38,713, 38,714, 38,716; U.K. Application No. 2,076,106A. h alzg-L-i-ns 64 o7espo 6 4- 7 e=ial 8-6 (Lutz) 250,491 (Jacobs et al) 273,52 a t-y)j274,010 (Wa1lty o 15 et al), 272,85 4k-ewatc et al), 300,709 (van Konynenburg o+ 6 0 0 (-Kama t h) e The resistivity of conductive polymers usually changes with temperature at a rate well above the I 0oa preferred temperatur:e coefficient of resistivity set out above, and the PTC conductive polymers often increase in resistivity by a 'actor of 10 or more over a 100°C range.

Accordingly it is important that in a locating member icomprising a conductive polymer jacket, at all tempera- I tUres likely to be encountered, e.g. at all temperatures 1 25 from 0° to 100°C, each longitudlnal section of the conductive polymer jacket has a resistance which is at least 100 times, 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 suibstantial contribution to the resistance of the elongate conductor, and any change in its resistance wih temeraturi is unimportant.

'4 p 4, V -24- MP0869 The second point on the locating member must have a known location, and it is normally a fixed point.

When the system is designed to detect different types of events occurring independently, the second point is preferably the same fixed point for detection of the differ. nt 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 4c 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.

0*9 THE SOURCE ',EMBER The source member preferably has the same general configuration and follows the same general path as th locating member. Thus it is preferred that the locating and source members are elongate members which follow the oo 0 same elongate path, often (but by no means necessarily) parallel to each other. If the adjacent ends of the source and locating members are connected to each other (through the power source), then a Wide variety of elongate electrical connection members will provide the necessary connection to the event-sensitive connection means and,where appropriate, also provide the event- 0 25 sensitive connection means. Thus the source member on be the same as, or: different from, the locatitng member.

Especially when the locating member is a wire electrically surrounded by a conductive polymer jacket, the source member is preferably a wire electrically surrounded by a conductive polyme jacket. The disclosure in Section 6 above about conductive polymers is also applicable to MP0869 the source member. The source mimb' preferably has substantially no reactance. In oQrer to reduce the input voltage required to provida a .ntrolled current in the test circuit, the source member can have a lower resistance per unit length than the locating member.

When the source and locating members are connected so as to provide a test circuit in which the only variable impedance is the connection between the source and locating members caused by the event, then the source member is preferably substantially identical to 0 o40 the locating member.

0 0 0 0 0 'a 0000 6000 So(8) THE RETURN MEMB SoIn many cases, the return member also has the same general configuration and follows the same general path as the locating member. This is preferred when .o.04 the return member is electrically connected to the 0 0. locating member at the ends thereof but is otherwise Insulated therefrom. On the other hand it is not oo OV( 20 necessary when the locating and source members follow a path in the form of a loop, since the return member can then be a relatively shoi#t member which joins (via the voltage-measuring device) the two ends of the locating ao member. The return member will usually follow the same general path as the source and locating members in another embodiment in which, when an event occurs, not only is a connection made between the locating and source members, but also an electrical connection of known resistance is made between the return member and the loaating member at the first point or lat some other -26point on the lociting member wrhich is further away from the second point. The return member preferably has substantially no reactance and can be conveniently be a simple insulated wire whose resistance per unit length is sufficiently low for the resistance of the return member to be ignored in obtaining the desired information about the event, e.g. less than 0.01 times the resistance per unit length of the locating member.

!0 ASSEMBLY OF THE ELONGATE CONNECTION MEMBERS The source and locating members, usually the return |member, the auxiliary member when present, and any other elongate members which noy be desired for checking continuity or to provide physical strength) can be combined together in any convenient way to provide a cable which can be positioned along the desired elongace path. If desired the return member, or the locating member, or a further member, can be relatively large and stroug, and thus be a strength member to which the other members are secured, e.g.

by wrapping, preferably in the form of a braid which may include additional elongate members. For a more detailed description of various wrapped configurations, reference should be made to European Application No. 85 300 415.8 (Publication No. 158,410) which includes the disclosure of U.S. Patent Application Nos 556,740 and 556,829 (MP0892) filed by Robert Wasley.

2 30 j10) USE OF SUBSTANTIALLY IDENTICAL LOCATING AND SOURCE MEMBER$ Very valuable improvements can be obtained through the use of a locating member wtioh has impedance characteristics such that, and which is connected so 'y1 file byRbr aly 8012S/MS -27- MP0869 that, the only variable impedance in the test circuit is the impedance of the connection which is created by the occurrence of the event. As noted above, this makes it possible to design a system which, at all points along its length, will be sensitive only to events which create a connection whose impedance is within a predetermined range. Another important advantage is that the impedance of the connection itsel can be measured. This can be done, for example, 00 0 000 0 0 0 0 0 o C 0 00 00 0 0 0a 0 00 0 4' 0 O 04 a c Ir 10 when a constant current source is used, by measuring the output voltage; when a constant voltage source is used, by measuring the current in the test circuit; or by including a switching arrangement so that, after the location of the event has been determined, a new circuit is created in which the voltage measured by the voltmeter is a measure of the impedance of the event.

When the locating member iE.h--o£C hskid-descr i T ed 20 i~ t- heap--a apl=io PO o 0-h) USen=wh-ickbh e atoeng=nmembe r includes a plurality of spaced-apart impedant components, the source member preferably comprises corresponding spaced-apart impedant components.

In order to make up such a system it is convenient to use pre-assembled modules which can be connected into the locating and source members to provide impedant components in those members and an event-sensitive connection member to connect those members when an event takes place. Such modules ai d-^ l R_ 1 -28- MP0869 hch-ei-c-cuit~t lzf i method for dEtecting and .Qbta ni n i n jfar-inahi n-A t- a P uindawbh--l U k COmprise a first impedant component having substantial impedance; a first conductor which has a relatively very small impedance and one end of which is connected to the first impedant component; a second impedant component having the same 10 impedance as the first impedant component; 0 4 a second conductor which has a relatively i 0oo very small impedance and one end of which is connected to the second impedant component; 0 the first impedant component and the first I 15 conductor, in the absence of an event, being electrically insulated from the second conductor and the second impedant component; and an event-sensitive connection means which, upon Soccurrence of an event, can effect electrical i 20 connection between the first and second conductors; the first impedant component and the first conductor being connectable in series with incoming and outgoing portions of an elongate electrically conductive locating member, and the second impidant component and the second conductor being connectable in series with incoming and outgoing portions of an elongate electric- S ally con6uctive source member. -erably the module also -29- MP0869 comprises a third impedant component connected to thu other end of the first conductor, and a fourth impedant component connected to the other end of the second conductor, the third and fourth components having the same impedance as the first and second components.

When using such a preferred module it does not matter whether the incoming portion of the locating member is connected to the first component and the outgoing portion of the locating member is connected to the third component, or vice versa. Similarly it does not matter whether the incoming portion of the source 0 4 0 member is connected to the second component and the 0°o outgoing portion of the source member is connected to o o the fourth component, or vice versa. This reduces the danger of incorrect installation of the system.

Indeed, if the event-sensitive connection means operates o in the same way whichever the direction of the current through it, it does not matter how the intermediate 0o portions of the source and locating members are connected 0 00 20 to the module, provided that the locating member is So0 connected through one of the conductors and the source member is connected through the other conductor.

0o t The module will often comprise a support member to which components to are secured; and/or a 0 0 25 housing which provides physical and/or e2ecIcal 0 k o protection for the components; and/or terminals for connecting the 'module as indicated above.

i MP0869 (11) THE POWER SUPPLY The current which is transmitted between the first and second points must be of known size, and is preferably supplied by a controlled current source, e.g. a galvanostat; however, a controlled voltage source can be used providing that a current-measuring device is included in the apparatus so that the location of the first point can be calculated. The current may be a continuous or pulsed direct current or an alternating current of regular sinusoidal or other form. The current which flows between the first and second points is often in a 10 milliamps, e.g. 0.5 to 3 milliamps. However, where very long paths are to be monitored for events, even lower currents can be employed, especially when using a Sreference impedance, as described 4 b sezed- and s f abl.y -M-t y. The controlled current source is preferably a fixed current source or a current source which can be S, adjusted to provide current of a desired and known value, for example to obtain improved accuracy in locating a fault which was detected at a lower current level. However, it is also possible to use a fixed Svoltage source, in combination with a current-measuring device which measures the current flowing between the 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, is otherwise insulated from the locating member.

i rp b.

-31- MPO869 (12) THE VOLTAGE-MEZSURING DEVICE The voltage-measuring device can be of any kind, and suitable devices are well known to those skilled in the art. Preferably the voltage-measuring device is a voltmeter which has a resistance of at least 10,000 ohms, preferably at least 1 megohm, especially at least megohms.

(13) PHYSICAL AND ELECTRICAL RELATIONSHIPS BETWEEN THE COMPONENTS OF THE APPARATUS As briefly indicated in the description of Figure 1, o9 Q 10 the physical and electrical relationships between the components of the apparatus of the invention can be widely varied.

It is also possible, as shown in Figure 2, for a plurality of event-detecting stations (which can detect the same or different events) to be positioned at locations which are remote from the locating member and to be electrically (or otherwise) connected to switches (eg.

electromagnetically operated relays) between the locating and source members.

a PARTICULAR EVENT-SENSITIVE-CONNECTION MEANS Figures 3-6 show cross-sections through apparatus of the invention.

Figure 3 is a cross-section through apparatus C for detecting an over-temperature fault condition.

__C

1 I 4 44 4, 4 I. ;c 44 44 '4 e 4*r e4 Locating member 11 and source member 12 are metal strips spaced apart by insulating strips 20, defining an air gap 21 between the conductors. Return member 16 and insulating jacket 161 surrounding it are also present. A bimetallic C-clip comprising metal strips 7 and 8 bears on the center portions of the scrips 11 and 12 through insulating pad 78; under normal conditions the clip is in the open position shown, but it is so constructed and arranged that if the temperature exceeds a particular value, the clip closes and brings the strips 11 and 12 into electrical contact.

Suitable C-clips can be composed of a spring steel member and a memory metal member. For example, if under normal conditions, the irner member 7 is composed of spring steel, and the outer member 8 is composed of a memory metal in the martensitic phase and is maintained in an expanded configuration by the member 7, then if the temperature reaches the transformation temperature of the memory metal, the member 8 will recover, overcoming the elastic resistance of the member 7 and bringing the strips 11 and 12 into 20 contact.

Figure 4 is somewhat similar to Figure 3, but makes use of a bimetallic member to bring a strip 12 and a wire 11 into electrical contact if the temperature falls below a articular level. Strip 12 is connected to a C-clip having an inner member 7 composed of spring steel and outer member 8 composed of a memory metal. The C-clip is separated from wire 11 by an air gap 21 in an apertured insulating member Under normal conditions, the memory metal member 8 is in the austenitic state and maintains the spring steel 30 member 7 in a compressed configuration so that there is no contact between strip 12 and wire 11, If the temperature drops below the transformation temperature of the memory metal, thus converting the member 8 into the weak martensitic state, the spring steel member expands and effects electrical connection between the strip 23 and the wire 11.

4 4 4 4 4* 5788S/ls -32p t In Figures 3 and 4, the C-member will generally comprise a plurality of discrete, spaced-apart, members.

However, a continuous C-member will also be satisfactory.

Figures 5 and 6 show apparatus for detecting an increase in pressure, for example for placing under a floor covering as a burglar alarm. The source member 12 is in the form of a metal strip and is surrounded by an insulating polymeric sheet 22 which has apertures 21 in its top surface. The locating member 11 is a constant resistance metal wire which is separated from the member 12 by insulating sheet 22 and crosses over the apertures 21. The return member 16 is placed below the second conductor and is insulated therefrom at all points. A flexible insulating polymeric jacket 92 surrounds the various components. Under normal conditions the locating and source members are not electrically connected. However, if the pressure on the top surface of the insulating jacket increases sufficiently, the locating member is forced through aperture 21 to contact the source member.

p I~ i~ p p p '4

S

£C~

I

p p C p.

I'

p f p 5788S/ls-3- -33-

Claims (3)

1. An elongate article which is suitable for use as the locating member in a method for monitoring for the occurrence of an event, and for detecting and obtaining information abo.ut the event upon its occurrence, which method comprises providing a system in which, upon occurrence of theievent, electrical connection is made between an electrically conductive locating member and an electrically conductive source member; the locating member and/or the source member comprising a metal core and an elongate jacket which electrically surrounds th' core and which is composed of a conductive polymer; 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 the connection, (b) that part of the locating member which lies between the first point and a second point having a known location on the locating member, and a power source which causes an electrical current of known size to be transmitted between the first and second points on the locating member; and V the current and the locating member being such that, by measuring the voltage drop between the first and second points, the spatial relationship betwen the first and second points can be determined; the voltage drop betwen the first and second points is measured; and 5788S/ s -34- information concerning the event is obtained from the measurement made in step said article comprising; an elongate core which is composed of a metal whose temperature coefficient of resistivity averages less than 0.003 per degree Centigrade over the temperature range 0° to 100°C and in which each longitudinal section has a resistance which is from 10 4 to 104 ohms/foot, and an elongate jacket which is composed of a conductive polymer, which electrically surrounds the core, and in which each longitudinal section 15 has a resistance which is at least 100 times the resistance of the core of that longitudinal section at all temperatures from 0° to 100'C.

2. An article according to claim 1 which has a resistance of 1 to 20 ohm/foot (3.3 to 65 ohm/meter) and a temperature coefficient of resistance which averages less than 0.0003 per degree Centigrade in the temperature range 0° to 100'C.

3. An elongate article which is suitable for use as a locating member in a method for monitoring for the occurrence of an event substantially as herein described with reference to any one of the Figures. DATED this 6th day of July, 1990 RAYCHEM CORPORATION By their Patent Attorneys GRIFFITH HASSEL FRAZER S8S/MS