Method for detecting and obtaining information about changes in variables

• US 5,382,909 A
• Filed: 07/30/1993
• Issued: 01/17/1995
• Est. Priority Date: 06/30/1983
• Status: Expired due to Term

• Current Assignee: Tyco Electronics Corporation (TE Connectivity Limited)
• Original Assignee: Raychem Corporation (TE Connectivity Limited)
• Inventors: Reed, James P., Welsh, Laurence, Frank, Louis M., Wasley, Robert S., Tolles, Thomas W., Masia, Michael, Lahlough, John, Reeder, Larry R., Brooks, Peter L., Stewart, Ray F., Bonomi, Mauro
• Primary Examiner(s): Regan, Maura K.
• Application Number:
  US08/100,710
• Time in Patent Office: 536 Days
• Field of Search: 324/522, 324/509, 324/525, 324/526, 324/512, 324/523, 324/539, 324/551, 324/691, 379/26, 346/602-605, 346/637, 174/11 R
• US Class Current: 324/522
• CPC Class Codes: G01D 11/00 Component parts of measuring arrangements not specially adapted for a specific variable G01D13/00, G01D15/00 take precedence
• CPC Class Codes: G01K 7/18 the element being a linear resistance, e.g. platinum resistance thermometer G01K7/26 takes precedence
• CPC Class Codes: G01M 3/045 with electrical detection means
• CPC Class Codes: G01M 3/165 by means of cables or similar elongated devices, e.g. tapes
• CPC Class Codes: G01M 3/18 for pipes, cables or tubes; for pipe joints or seals; for valves; for welds; for containers, e.g. radiators
• CPC Class Codes: G01N 27/048 for determining moisture content of the material
• CPC Class Codes: G01R 31/08 Locating faults in cables, transmission lines, or networks
• CPC Class Codes: G01R 31/083 in cables, e.g. underground
• CPC Class Codes: G08B 23/00 Alarms responsive to unspecified undesired or abnormal conditions
• CPC Class Codes: G08B 25/018 Sensor coding by detecting magnitude of an electrical parameter, e.g. resistance
• CPC Class Codes: H01H 35/42 Switches operated by change of humidity

Abstract

Detection of liquid leaks and other changes in variables is disclosed. The event causes two elongate conductors to become electrically connected at a location which is determined by the event, thus creating a system in which the connection point can be located by measuring the potential drop from one end of one of the conductors (called the locating member) to the connection point. The system comprises a balancing component so that its sensitivity is not dependent on the location of the event along an elongate path. A fixed current flows through the connection, so that the result is independent of the resistance of the connection. The locating member can be a continuous resistive wire, coated with a conductive polymer; such a locating member can form part of a sensor cable in which the elongate components of the circuit are in a wrapped configuration. Alternatively the locating member comprises a plurality of discrete resistors. The system is arranged so that only connections within a certain range of resistance will activate the system. The voltage drop is calculated by comparing it to the voltage drop over a resistor of known size. Particular event-sensitive connection means are employed for the detection of hydrocarbons.

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

(1) providing a system

(a) which comprises a power source, a voltage-measuring device, an elongate electrically conductive locating member and an elongate electrically conductive source member, the locating member comprising a plurality of available connection points and having an impedance Z_total between the most widely separated available connection points, and

(b) in which, upon occurrence of the event,

electrical connection is made between the locating member and the 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 (i) that part of the locating member which lies between the first point and a second point having a known location on the locating member, (ii) the connection, (iii) the power source, and (iv) a balancing component which is connected in series with said part (i) and which has an impedance substantially equal to the difference between Z_total and the impedance of said part (i), the power source causing 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) monitoring the system to determine when a said connection has been made, said test circuit being in existence while said monitoring is taking place if a said connection has been made; and

(3) when it is determined that a said connection has been made, using the voltage-measuring device to determine the voltage drop between the first and second points; and

(4) obtaining information concerning the event from the measurement made in step (3).

2. A method according to claim 1 wherein the system includes

a reference impedance which has a known impedance and which forms part of the test circuit and wherein the size of the electrical current transmitted between the first and second points on the locating member has a known relationship with the current through the reference electrode;

and wherein

the currents the reference impedance and the locating member are such that, by obtaining a ratio between a first voltage drop across the reference impedance and a second voltage drop between the first and second points on the locating member, the spatial relationship between the first and second points can be determined.

3. A method according to claim 1 wherein the system comprises

a swellable member which swells upon occurrence of the event, and which has at least one of the following characteristics

(a) on swelling it causes an electrical path to be formed between the locating member and the source member through the apertures of an apertured separator, and

(b) it is a conductive, bridging member which, upon occurrence of the event, swells into contact with the locating member and the source member and bridges the members, whereby an electrical connection is made between the members.

4. A method according to claim 3 wherein the locating member, the source member and the swellable member are part of a device which comprises

i) an elongate support core,

ii) the locating and source members helically wrapped around the core,

iii) a separator in the form of a braid surrounding the locating and source members,

iv) the swellable member in the form of a hollow swellable member which comprises a conductive polymer and which surrounds the the separator braid, and

v) a restraining braid surrounding the conductive polymer,

and wherein, upon occurrence of an event, the swellable member swells through the apertures of the separator braid, and contacts and bridges locating and source members and makes an electrical connection between them.

5. A method according to claim 3 wherein the locating member, the source member and the swellable member are part of a device which comprises

an elongate support core having a uniform cross-section along its length;

ii) a spacer member;

iii) the locating member;

iv) the source member in the form of a member which is hollow and surrounds the support core, spacer member and locating member; and

(v) the swellable member;

said spacer member projecting outwardly from the support core a greater distance than the locating member such that in the absence of an event it spaces the source and locating members from each other.

6. A method according to claim 1 wherein the source member and the locating member are identical.

7. A method according to claim 1 wherein the locating member (a) has a temperature coefficient of impedance which averages less than 0.003 per degree over the temperature range 0°

to 100°

C. and (b) comprises an elongate metal core which is physically and electrically surrounded by a jacket of a composition which comprises a polymeric component and, dispersed in the polymeric component, a sufficient amount of carbon black to render the composition conductive at ambient temperatures.

8. A method according to claim 1 wherein

(a) the system comprises an elongate electrically conductive auxiliary member,

(b) the locating, source and auxiliary members follow an elongate path having a near end and a far end,

(c) the second point on the locating member is at the near end of the path,

(d) the auxiliary member is electrically connected to the source member at the far end of the path, and

(e) the locating and source members have substantially the same impedance characteristics.

whereby the balancing component (iv) in the test circuit is provided by that part of the source member which lies between the first point and the far end of the hath.

9. A method according to claim I wherein

(1) the power source in the test circuit has an output voltage V volts and causes an electrical current I amps of known size to be transmitted between the first and second points on the locating member;

and

(2) information concerning the event is obtained only when the value of the ratio V/I is within a predetermined range.

10. Apparatus for detecting an event which comprises

(1) an elongate electrically conductive locating member which comprises a plurality of available connection points which has an impedance Z_total between the most widely separated available connection points, and whose impedance from one end to any of the connection points defines the spatial relationship between that end and that connection point;

(2) an elongate electrically conductive source member;

(3) an event-sensitive connection means which is present at said plurality of available connection points and which, upon occurrence of an event at any of said available connection points permits or effects electrical connection between the locating member and the source member at one or more of the connection points, 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 (i) that part of the locating member which lies between the first and second points, (ii) the connection, (iii) the power source, and (iv) a component which is connected in series with said part (i) and which has an impedance substantially equal to the difference between Z_total and the impedance of said part (i), the power source causing an electrical current of known size to be transmitted between the first and second points on the locating member.

11. Apparatus according to claim 10 wherein the power source is a controlled current source.

12. Apparatus according to claim 10 for detecting and locating, along a longitudinally extending path having a near end and a far end, a change in an ambient condition from a first state to a second state, in which apparatus

(a) the source member lies along said path and has a near end at the near end of the path and a far end at the far end of the path;

the locating member

(i) lies along said path and has a near end at the near end of the path and a far end at the far end of the path, the near end of the locating member being electrically connected to the near end of the source member

(ii) is electrically insulated from the source member at all points along the path when said ambient condition is in the first state at all points along the path,

(iii) when said ambient condition changes from the first state to the second state at at least one point along the path, becomes electrically connected to the source member at a connection point at which said ambient condition has changed from the first state to the second state, thereby creating a test circuit which includes part of the source member and part of the locating member and

(iv) has an impedance from the near end to each point thereon which is characteristic of its length from the near end to that point;

(c) the power Source is a controlled current source which forms part of the test circuit created when said ambient condition changes from the first state to the second state;

and which apparatus further comprises

(d) an elongate electrically conductive return member which has a near end at the near end of the path and a far end at the far end of the path, which is electrically insulated from the source member and the locating member between its near end and its far end when said ambient condition is in its first state and when it is in its second state, and which connects the near end and the far end of the locating member thus forming a reference circuit which contains the

voltage-measuring device said voltage-measuring device having a very high input impedance by comparison with the other components of the reference circuit;

the source member, the locating member, and the return member being physically secured together and at least one of the first, second and third connection means having a wrapped configuration;

whereby it is possible to monitor the voltage-measuring device, and when the voltage measured by the voltage-measuring device changes, to measure the change in the voltage and to calculate therefrom the distance between the near end of the locating and the connection point.

13. Apparatus according to claim 10 wherein the locating member and the source member are wrapped parallel to each other around an insulating core.