EVENT LOCATION USING A LOCATING MEMBER CONTAINING DISCRETE IMPEDANCES

Abstract: 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 a 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, three conductors follow an elongate path. One of them (called the locating member (11)) compris­ es a plurality of spaced-apart resistors (111) separated by low resistance intermediate components (112), so that the locat­ ing member has known impedance characteristics along its length. The second conductor (12) is connected to one end of the locating member, but is otherwise insulated from the locating member. When the event occurs, connection is made between the locating member (11) and the second conductor (12) at one or more of a plurality of available connection points, each of which lies between a pair of resistors. With the aid of the third conductor (16), a current of known size is passed through, and the voltage drop is measured between, the connection point and one end of the locating member. The location of the event can then be calculated.

Description: DESCRIPTION EVENT LOCATION USING A LOCATING MEMBER CONTAINING DISCRETE IMPEDANCES This invention relates to methods and apparatus for detecting and obtaining information about (particularly locating) changes in variables, and is related to the application already filed corresponding to U.S. Serial Nos. 509,897 and 457,882 (MP0869-US1 and US2) and to the application being filed at the same time as this application corresponding to U.S. Serial No. 599,048 (MP0869-US3), which are referred to herein as the Masia/Reed applications. Introduction to the Invention A number of methods have been 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 temperature, 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. 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". 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. The Masia/Reed applications describe improved systems in which the location of an event is determined by measuring the voltage drop down a locating member having known impedance characteristics and to which connection is made when an event takes place. The application already filed corresponding to U.S. Serial Nos. 556,740 and 556,829 (MP0892) describes preferred ways of assembling the locating, return and source members, at least one of the members having a wrapped configuration, and the application being filed at the same time as this application corresponding to U.S. Serial No. 603,484. (Bonomi/Frank, MP0932-USl); describe modifications of the Masia/Reed systems. In the copending applications referred to above, a key feature is that, under the conditions of operation, the impedance of the locating member changes in a known fashion along the length of the member. SUMMARY OF THE INVENTION I have now discovered that great benefits can be obtained, in the methods and apparatus disclosed in the Masia/Reed applications, from the use of a locating member which comprises (a) a plurality of spaced-apart discrete impedant components, each of which has substantial impedance, and (b) a plurality of elongate intermediate com ponents, each of which physically separates and electrically connects a pair of impedant components. When such a locating member is used, the system is arranged so that, upon occurrence of an event, connection is made to the locating member at one or more of a plurality of available connection points, each of which lies between two impedant components. As a result, a plot of the possible voltage drops against the distance from the second point (usually one end of the locating member) to the first point has a succession of discontinuities in it, corresponding to the impedant components. In one aspect, the invention 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, (1) electrical connection is made between an electrically conductive locating member and an electrically conductive second member; the locating member comprising (a} a plurality of spaced-apart, discrete impedant components, each of which has substantial impedance, and (b) a plurality of elongate intermediate com ponents, each of which physically separa tes and electrically connects a pair of impedant components; the connection to the locating member being made at at least one of a plurality of available connection points which lie between the impedant components, and the connection 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 that part of the locating member between the first point and a second point on the locating member having a known location, and in which an electrical current of known size is 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 (3). In another aspect, the invention provides an apparatus for detecting -and obtaining information about an event, which apparatus comprises (1) an elongate electrically conductive locating member which comprises (a) a plurality of spaced-apart, discrete impedant components, each of which has substantial impedance, and (b) a plurality of elongate intermediate mem bers, each of which physically separates and electrically connects a pair of impe dant components: : (2) an elongate electrically conductive second member; (3) a plurality of event-sensitive connection means, each of which, upon occurrence of an event can effect electrical connection between the locating member and the second member, the connection being made at at least one of a plurality of discrete available connection points which lie between the impedant com ponents, and the connection being effective at a first point on the locating member which is defined by at least one characteristic of the event; (4) an electrically conductive third member; (5) 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 (6) a power source which is electrically connected to the second point on the locating member and, which, at least when occurrence of an event causes electrical connection to be made between the locating and second members, causes a current of known size to be transmitted between the first and second points on the locating member. In another aspect, the invention provides an eventsensitive module which is suitable for use in the method and apparatus defined above and which comprises (1) an impedant component having substantial impe dance; (2) a first conductor which has a relatively very small impedance and which is connected in series with the impedant component; (3) a second conductor which also has a relatively very small impedance and which, in the absence of an event, is electrically insulated from the first conductor and the impedant com ponent; and (4) an event-sensitive connection means which, upon occurrence of an event, effects electri cal connection between the first and second conductors: the 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 conductor being connectable in series with incoming and outgoing portions of an elongate electrically conductive second member. The module will often comprise a support member to which components (1) to (4) are secured; and/or a housing which provides physical and/or electrical protection for the components; and/or terminals for connecting the module as indicated above. BRIEF DESCRIPTION OF THE DRAWING The invention is illustrated in the accompanying drawing in which Figures 1 to 4 are schematic circuit diagrams of the method and apparatus of the invention, and Figures 5 to 8 are circuit diagrams of event sensitive modules of the present invention. DETAILED DESCRIPTION OF THE INVENTION The invention is of particular value when it is desired to monitor for a change in a variable which can only take place at one or more of a plurality of discrete locations. One example of such a situation is in a chemical process plant where the position of valves is to be monitored. Another example is a building in which the positions of doors or windows are to be monitored. The invention is also particularly valuable for monitoring a system in which a change in a variable can take place at a number of different locations (which may be continuous or discrete), but in which it is possible to select a relatively small number of discrete locations as providing an adequate basis for monitoring. One example of such a situation is where the existence of a leak from a tank can be adequately monitored by placing a single leak detector at a low point beneath the tank, or by placing a plurality of leak detectors at spaced locations beneath the tank. In situations such as those outlined above, an event-sensitive connection means is placed at each of the discrete locations, and at least one impedant component is placed in the locating member between each event-sensitive connection means. Usually it will be convenient for a single impedant component to be placed adjacent the event-sensitive connection means, preferably making use of an event-sensitive module which comprises (1) an impedant component which can be connected in series with intermediate components of the locating member, (2) an electrical connection means which can be connected in series with parts of the second member, and (3) an event-sensitive connection means which, upon occurrence of an event, can effect electrical connection between the locating member and the second member. Such modules are novel and form part of the present invention. The invention is also particularly useful when it is desired to monitor a system which includes a number of branch lines along each of which a change in a variable can take place in a number of different locations (which may or may not be discrete), but in which system it is adequate to know, when a change in a variable has taken place along one of the branch lines, which of the branch lines is involved. In such situations, one or more event-sensitive connection means (including continuous event-sensitive connection means) are placed along each of the branch lines. As previously noted, a key feature of the earlier applications is that, under the conditions of operation, the impedance of the locating member is dependent substantially only on the distance between the first and second points. The extent of any permissible Variation in the impedance will of course be dependent on the accuracy with which the location of the first point must be calculated. This means, for example, that if (as is often the case) the temperature may vary along the length of the locating member, it is necessary, when calculating the location of the first point from the voltage drop, either (a) to compensate for any change in impedance with temperature (which can only be done if the change in temperature and the temperature coefficient of impedance are known), or (b) to make use of a locating member which has a very low temperature coefficient of impedance. In practice, alternative (b) has been greatly preferred, leading to the use of locating wires which are made of Constantan or another alloy having a very low temperature coefficient of impedance. One of the advantages of the present invention is that if, as is preferred, there is at most one available connection point between each pair of adjacent impedant components, then the accuracy of the information obtained about the event is not affected by unknown variations in the impedance of one or more of the components of the locating member, providing that the total variation in the impedance of the locating member, between the first and second points, is substantially less than the impedance of any one of the impedant components. This follows from the fact that a plot of distance against possible voltage drop, along the locating member, shows a series of discontinuities. The same is true when there is more than one available connection point between each pair of adjacent impedant components, providing that the only information required is that an event has taken place at some point between two impedant components, without any need to identify more precisely the location of the event. Thus in the present invention, it is possible, for example, to use standard insulated copper wire to provide the elongate intermediate components of the locating member, and to use standard resistors as the impedant components of the locating member. Preferably each of the impedant components has an impedance which is substantially higher than, particularly at least 100 times, especially at least 1000 times, the total impedance of all of the intermediate components. Preferably both the impedant and the intermediate components have resistance but substantially no reactance. The resistors used as impedant components can for example have a resistance of at least 0.1 ohms, particularly 1 to 1000 ohms. The impedant components can all be the same or they can be different. The intermediate components can be of the same or different lengths, depending on the distances between the locations of the desired available connection points. Preferably each of the intermediate components is of the same cross-section throughout its length, and the different intermediate components have the same cross-section. As those skilled in the art will realize, the "electrical center" of a plurality of discrete connections can be calculated if the resistances of all the components in the various circuits are known. The ability to make this calculation is of no value when connection to the locating member can be made at any point along its length, or at any point along extended sections of its length. It is also of no value when the resistances of the different connections are unknown. It is also of little or no value when connection to the locating member can only be made at discrete points and the impedance of the locating member varies con tinuously with its distance from the second point. However, when the locating member comprises a plurality of discrete impedant components of known size, as in the present invention, and the impedances of the various different components which can form part of the test circuit are known, then in many cases it is possible, by appropriate selection of the various impedances, to design a system in which it is possible to ascertain, from the voltage drop shown by the voltagemeasuring device, which combination of connections has been made Thus the invention includes methods and apparatus- in which the connections which can be made, upon occurrence of an event, are of known impedance, and the impedant components are selected so that, when connection is made between the locating and second members, each combination of possible connections gives rise to a voltage drop which is unique to that combination or which is characteristic of one of a relatively small number of combinations. The impedances of the various available connections can be the same or different (and can be substantially zero). Thus one or more of the available connections can have associated therewith an additional impedant component so that when (but only when) connection is made at that available connection point, an additional known impedance is introduced into the test circuit. The additional known impedance can be introduced into the connection between the locating and second members and/or into the locating member. It is also possible to arrange the switching, when an event occurs, so that an impedant component is removed from the locating member. The number of available connections which can be placed in a system of this kind will depend inter alia upon the precision with which the various impedances are known, the accuracy of the voltage-measuring device, and the number of combinations which the use of the system will allow any particular voltage drop to represent. Referring now to Figure 1, this shows a system of the general kind disclosed in EP0869-US1 and US2. It comprises a locating member 11; a second (or source) member 12 which is connected through a constant current source 15 to end (2) of the locating member 11, but in the absence of an event is otherwise insulated from the locating member; and a third (or return2 member 16 which is connected to both ends of the locating member throngh a voltage-measuring device 14. The system of Figure 1 differs from that shown in MP0869-US1 and US2 in that the locating member comprises a plurality of space:#-apart resistors 111 separated by low resistance intermediate components 112; in Figure 1 and the other Figures, all the intermediate components are shown as beinc of the same short lengths, but in practice they can be of different lengths and can be short or long, e.g. rom less than 1 meter to many hundreds of meters. At spaced-apart locations along the locating and second members, are placed event-sensitive connection means, which are shown as switches 5 but could be any connection means which, upon occurrence of the event, will make a connection of any- kind between the two members. Figure 2 is similar to Figure 1 but shows a system of the general kind disclosed in MP0869-US3, i.e. a system of which the source member 12 is connected to both ends of the locating member, and the return member 16 is connected to end (2) of the locating member but otherwise becomes connected to the locating member only through the event-connection means, which in this system must make a connection of known impedance between the locating and return members. Just as the system of Figure 1 differs from the system of MP0869-US1 and MP0869-US2, so also the system of Figure 2 differs from the system of MP0869-US3 by the use of a locating member comprising impedant components (resistors 111) and intermediate components 112. Figure 3 is similar to Figure 1, but includes the modification disclosed in the Bonomi/Frank application (MP0932-USl), namely the use of a reference resistor Rf connected in series with the locating member and two voltmeters 141 and 142 connected across the reference resistor and the locating member respectively; in this way, the location(s) at which switch(es) S has(have) closed, due to occurrence of an event, can be determined by comparing the voltage drops down the locating member and the reference resistor. Figure 4 is similar to Figure 1, but makes use of resistors 114, 115, 116, 117, and 118 in place of resistors 112, and includes resistors 61, 62, 63, 64, and 65 which are brought into the test circuit when the corresponding switch S closes upon occurrence of an event. The sizes of the resistors 114, 115, 116, 117, 118, 61, 62, 63, 64, and 65 are selected so that each possible combination of switch closures gives rise to a unique voltage drop. Figures 5, 6 and 7 are circuit diagrams of modules which are especially useful for systems of the general kind shown in Figure 4. By making use of a plurality of gauged switches, S1, S2 and S3, which are operated together by the occurrence of an event at the module, (1) in Figure 5, an additional resistor 119 is introduced into the locating member. (2) in Figure 6, resistor 111 is removed from the locating member and resistor 61 is introduced into the connection; and (3) in Figure 7, resistor 111 is removed from the locating member and resistor 120 is introduced into the locating member Modules of this kind can be used to increase the number of possible combinations of events which can give rise to unique voltage drops. Referring now to Figure 8, this shows a module suitable for use when setting up a system which includes a number of branch lines, along each of which an event can take place, and in which system it is adequate to know, when an event has taken place on one of the branch lines, which of the branch lines is involved. Thus in Figure 8, the module provides a branch line 40 which comprises a first elongate conductor 124 for connection into the source member 12 of a system as shown in Figure 1, a second elongate conductor 114 and resistor 111 for connection into the locating member 11 of a system as shown in Figure 1, and a plurality of event-sensitive modules S which will connect the conductors 114 and 124 if an event takes place. Alternatively conductors 114 and 124 could be bare wires, or wires covered by conductive polymer, which would become connected if electrolyte was present in sufficient quantity at any point along the branch line.

Claims: CLAIMS: 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 second member; the locating member comprising (a) a plurality of spaced-apart, discrete impedant components, each of which has substantial impedance, and (b) a plurality of elongate intermediate com ponents, each of which physically separa tes and electrically connects a pair of impedant components; ; the connection to the locating member being made at at least one of a plurality of available connection points which lie between the impedant components, and the connection being effective at a first point whose location is defined by at least one charac teristic of the event; the making of the connection enabling the formation of a test circuit which comprises that part of the locating member between the first point and a second point on the locating member having a known location, and in which an electrical current of known size-is 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 (3). 2. A method according to claim I wherein there is a single available connection point between each pair of impedant components and each of the impedant components is substantially identical. 3. A method according to claim 1 or 2 wherein the impedant and intermediate components have resistance but no reactance, and each of the impedant components has a resistance of at least 0.1 ohm, preferably 1 to 1000 ohms. 4. A method according to claims 1, 2 or 3 wherein the ratio of the impedance of each of the impedant com ponents to the total impedance of all of the intermediate components is at least 100, preferable at least 1000 5. A method according to any one of the preceding claims wherein at least one of the available connection points has associated with it an additional impedant component so that, when, but only when, connection is made between the locating and second members at that available connection point, an additional known impedance is introduced into the test circuit. and said impedant components and additional impedant components are selected so that each possible combination of connections gives rise to a unique voltage drop between the first and second points. 6. A method according to any one of the preceding claims wherein the system comprises a plurality of event-sensitive modules, each of which comprises (a) a said impedant component; (b) a first conductor which has a relatively very small impedance and is connected in series with the impedant component; (c) a second conductor which also has a relatively very small impedance and which, in the absence of an event, is electrically insulated from the first conductor and the impedant com ponent; and (d) an event-sensitive connection means which, upon occurrence of an event, can effect electrical connection between the first and second conductors; the first conductors and the impedant components forming part of the locating member and the second conductors forming part of the second member, and each of the locating member and the second member comprising a plurality of intermediate components which connect the event-sensitive modules. 7. A method according to claim 6 wherein at least one of the first and second conductors comprises a metal core which is electrically surrounded by a jacket which is composed of a conductive polymer, and the event is an increase in the amount of electrolyte to a level sufficient to effect electrical connection between the locating and second members. 8. Apparatus for detecting and obtaining information about an event, by a method as claimed in any one of claims 1 to 7, which apparatus comprises (1) an elongate electrically conductive locating member which comprises (a) a plurality of spaced-apart, discrete impedant components, each of which has substantial impedance, and (b) a plurality of elongate intermediate mem bers, each of which physically separates and electrically connects a pair of impe dant components; (2) an elongate electrically conductive second member; ; (3) a plurality of event-sensitive connection means which, upon occurrence of an event can effect electrical connection between the locating member and the second member, the connection being made at at least one of a plurality of discrete available connection points which lie between the impedant com ponents, and the connection being effective at a first point on the locating member which is defined by at least one characteristic of the event; (4) an electrically conductive third member; (5) 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 (6) a power source which is electrically connected to the second point on the locating member and, which, at least when occurrence of an event causes electrical connection to be made between the locating and second members, causes a current of known size to be transmitted between the first and second points on the locating member. 9. An event-sensitive module which is suitable for use in a method for detecting and obtaining information about an event, as claimed in any one of claims 1 to 7 and which comprises (1) an impedant component having substantial impe dance; (2) a first conductor which has a relatively very small impedance and which is connected in series with the impedant component; (3) a second conductor which also has a relatively very small impedance and which, in the absence of an event, is electrically insulated from the first conductor and the impedant com ponent; and (4) an event-sensitive connection means which, upon occurrence of an event, can effect electrical connection between the first and second conductors; the 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 conductor being connectable in series with incoming and outgoing portions of an elongate electrically conductive second member.

Inventors: HAUPILY, PAUL D.
Applicants: RAYCHEM CORPORATION (A DELAWARE CORPORATION)
Application year: 1985
Main classification: G01R31
IPC codes: G01B7, G01M3, G06F3, G01R31