CA1276254C - Method for detecting and obtaining information about changes in variables - Google Patents
Method for detecting and obtaining information about changes in variablesInfo
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- CA1276254C CA1276254C CA000478820A CA478820A CA1276254C CA 1276254 C CA1276254 C CA 1276254C CA 000478820 A CA000478820 A CA 000478820A CA 478820 A CA478820 A CA 478820A CA 1276254 C CA1276254 C CA 1276254C
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- current
- source
- voltage
- locating member
- event
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Abstract
ABSTRACT OF THE DISCLOSURE
An improved method and apparatus for detecting and 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 moveable member such as a valve, a change in tem-perature, or a change in pressure. The apparatus includes an elongate locating member to which connec-tion is made at the location of the event, an elongate source member which supplies current to the locating member through the connection which is made when an event occurs, and a return member to measure the voltage drop down the locating member. The apparatus includes means for ensuring that the apparatus does not signal an event if the impedance of the connection to the locating member is above a predetermined value.
This eliminates false alarms resulting from circumstan-ces which result in high impedance connection between the locating and source members.
An improved method and apparatus for detecting and 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 moveable member such as a valve, a change in tem-perature, or a change in pressure. The apparatus includes an elongate locating member to which connec-tion is made at the location of the event, an elongate source member which supplies current to the locating member through the connection which is made when an event occurs, and a return member to measure the voltage drop down the locating member. The apparatus includes means for ensuring that the apparatus does not signal an event if the impedance of the connection to the locating member is above a predetermined value.
This eliminates false alarms resulting from circumstan-ces which result in high impedance connection between the locating and source members.
Description
~:76'~:~i4 BACKGROUND OF THE INVENTION
, Field of the Invention This invention relates to methods and apparatus for detecting and obtaining informatian about (particularly locating) changes in variables, and is related to the invention disclosed and claimed in Canadian Patent Application Serial No. 457,882, filed on June 29, 1984, in the name of Raychem corporation refer-red to herein as the Masia/Reed application.
Introduction to the Invention A number of methods have been used (or proposed for use) to detect changes in variables along an elongate path, e.g.
the occurrence of a leak (of water or another liquid or gas), insufficient or excessive pressure, too high or too low a temper-ature, 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". Such detection methods are for example highly desirable to detect leaks from steam lines into thermal insulation surrounding such lines, leaks from tanks and pipes containing corrosive or noxious chemicals, or leakage or conden-sation of water under floors or within telecommunication or electrical power systems. Some of these known methods not only signal when the event takes place, but also indicate the location '~
`` ~ 276i~54 of the event. However, the methods which were known prior to the filing of the Masia/Reed applications and which indicate the loca-tion of the event suffer from serious disadvantages. For example, they make use of time domain reflectometer techniques (and are, therefore, expensive), andfor give unreliable results when used over usefully long elongate paths or under conditions when there may be a substantial and unknown variation along the length of the path of a variable which affects the accuracy of the measurement (especially temperature), and/or make use of electrical conduc-tors whose primary purpose is to carry a current (e.g. a telecom-munication signal) under normal operating conditions (and which therefore have resistance and uniformity characteristics consis-tent with that purpose), and/or cannot be used when the event causes electrical connection between two conductors through a connection which is of high or indeterminate resistance, e.g. an ionically conductive connecting element. 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.
Canadian Application Serial No. 457,882 describes an improved method and apparatus for monitoring for the occurrence of an event, and for detecting and obtaining infor-~2762~i4 _3_ 26918-74 mation about the event upon its occurrence (i.e. as soon as it occurs or at some time after it has occurred). In that method, upon occurrence of the event, an electrical connection is made between a source member and a locating member of known impedance characteristics, the connection(s) being effective at a first point at which the event takes place (or whose location is defined by some other characteristic of the event). A current of known size is then driven through the electrical connection and down the locating member to a second point whose location is known. The voltage drop between the first and second points is measured and the location of the first point can then be determined. The system preferably makes use of a locating member having an impedance which is selected to give a desired degree of accuracy in locating the first point, and which preferably does not vary substantially within the temperature range in which the system operates. For many uses, a particularly important advantage is that the infor-mation obtained can be independent of the impedance of the connec-tion 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 the system of Canadian Patent Application Serial No.
457,882, the voltage drop between the first and second points is preferably determined by means of a voltage-measuring device which forms part of a reference circuit, the reference circuit comprising:
(a) the voltage-measuring device, lZ7~i25~
, Field of the Invention This invention relates to methods and apparatus for detecting and obtaining informatian about (particularly locating) changes in variables, and is related to the invention disclosed and claimed in Canadian Patent Application Serial No. 457,882, filed on June 29, 1984, in the name of Raychem corporation refer-red to herein as the Masia/Reed application.
Introduction to the Invention A number of methods have been used (or proposed for use) to detect changes in variables along an elongate path, e.g.
the occurrence of a leak (of water or another liquid or gas), insufficient or excessive pressure, too high or too low a temper-ature, 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". Such detection methods are for example highly desirable to detect leaks from steam lines into thermal insulation surrounding such lines, leaks from tanks and pipes containing corrosive or noxious chemicals, or leakage or conden-sation of water under floors or within telecommunication or electrical power systems. Some of these known methods not only signal when the event takes place, but also indicate the location '~
`` ~ 276i~54 of the event. However, the methods which were known prior to the filing of the Masia/Reed applications and which indicate the loca-tion of the event suffer from serious disadvantages. For example, they make use of time domain reflectometer techniques (and are, therefore, expensive), andfor give unreliable results when used over usefully long elongate paths or under conditions when there may be a substantial and unknown variation along the length of the path of a variable which affects the accuracy of the measurement (especially temperature), and/or make use of electrical conduc-tors whose primary purpose is to carry a current (e.g. a telecom-munication signal) under normal operating conditions (and which therefore have resistance and uniformity characteristics consis-tent with that purpose), and/or cannot be used when the event causes electrical connection between two conductors through a connection which is of high or indeterminate resistance, e.g. an ionically conductive connecting element. 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.
Canadian Application Serial No. 457,882 describes an improved method and apparatus for monitoring for the occurrence of an event, and for detecting and obtaining infor-~2762~i4 _3_ 26918-74 mation about the event upon its occurrence (i.e. as soon as it occurs or at some time after it has occurred). In that method, upon occurrence of the event, an electrical connection is made between a source member and a locating member of known impedance characteristics, the connection(s) being effective at a first point at which the event takes place (or whose location is defined by some other characteristic of the event). A current of known size is then driven through the electrical connection and down the locating member to a second point whose location is known. The voltage drop between the first and second points is measured and the location of the first point can then be determined. The system preferably makes use of a locating member having an impedance which is selected to give a desired degree of accuracy in locating the first point, and which preferably does not vary substantially within the temperature range in which the system operates. For many uses, a particularly important advantage is that the infor-mation obtained can be independent of the impedance of the connec-tion 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 the system of Canadian Patent Application Serial No.
457,882, the voltage drop between the first and second points is preferably determined by means of a voltage-measuring device which forms part of a reference circuit, the reference circuit comprising:
(a) the voltage-measuring device, lZ7~i25~
(b) that part of the locating member which lies between the first and second points, and (c) an electrically conductive return member which (i) is electrically connected to the locating member at the second point and at another point on the locating member whose distance from the second point is at least as great as the distance from the second point to the first point, both distances being measured along the locating member, and (ii) is otherwise insulated from the locating member, the voltage-measuring device having an impedance which is ~ery high by comparison with any unknown part of the impedance of the other components of the reference circuit.
Canadian Patent Application Serial No. 478,813 filed on April 11, 1985 in the name of Raychem Corporation describes a ~ystem which is somewhat similar to that referred to in the pre-vious paragraph, but differs from it in that (a) the source mem-ber is connected to the locating member, so that current can pass through the locating member in the absence of an event, and, (b) upon occurrence of the event, electrical connection is made between the locating member and the return member. Thus Canadian application 478,813 provides a novel method for monitoring for the occurrence of an event, and for detecting and obtaining informa-tion about the event upon its occurrence, which :
lZ7~Z54 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 return member;
the connection to the locating member being effective at a first point whose location is defined by at least one characteristic of the event;
the making of the connection enabling the formation of a test circuit which comprises (a) the connection, (b) that part of the locating member which lies between the first point and a second point having a known location on the locating member, and (c) a voltage-measuring device which has an impedance which is very high by comparison with any unknown part of the impedance of the other components of the test circuit;
~2) there is provided a reference circuit which comprises (a) a source member which is electrically connected to the second point on the locating member and to a point on the locating member whose distance from the second point is at least as great as the distance from the second point to the first point, both distances being measured along the locating member, and which is otherwise electrically insulated from the locating member, ~Z762~4 (b) that part of the locating member which lies between the first and second points, and (c) a power source which causes an electrical current of known size to be transmitted between the first and second points on the locating member; the cur-rent 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;
(3) the voltage-measuring device is used to measure the voltage drop between the first and second points; and (4) information concerning the event is obtained from the measurement made in step (3).
Canadian Patent Application Serial No. 468,974 filed on November 29, 1984 in the name of Raychem Corporation describes preferred ways of assembling the locating, return and source members, at least one of the members having a wrapped configura-tion.
Canadian Patent Application Serial No. 478,817 filed on April 11, 1985 in the name of Raychem Corporation describes a modification of the systems of Canadian applications 457,882 and 478,813 in which a reference impedance is placed in series with the locating member, and the location of the first point on the locating member is determined from the ratio of the voltage drops down the locating member and the reference impedance.
!l ~276254 Canadian Patent Application Serial No. 478,819 filed on April 11, 1985 in the name of Raychem Corporation discloses a modification of the systems of Canadian applications 457,882 and 478,813 in which the locating member comprises (a) a plurality of spaced-apart discrete impedant components, each of which has substantial impedance, and (b) a plurality of elongate intermediate components, each of which physically separates and elec-trically connects a pair of impedant components.
When such a locating member is used, the system isarranged 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 com-ponents.
Canadian Patent Application Serial No. 478,818 filed on April 11, 1985 in the name of Raychem Corporation discloses a modification of the system of Canadian application 457,882 in which the system is so arranged that the only variable impedance in the test circuit is the impedance of the connection between the source and locating members.
~2762~;4 In the systems described in the aforementioned applica-tions, a key requirement is that a current of known size is driven down the locating member. In order to supply such a current, a controlled current source is preferably employed.
SUMMARY OF THE I~VE~TIO~
In making use of systems as described in Canadian application Serial No. 457,882, using a controlled current source, delivering a "fixed" current, in order to detect the presence of electrolytes, we found that false information was sometimes obtained. We further discovered that this false information was obtained when a very small amount of electrolyte was present, so that the locating and source members were connected to each other through a connection whose resistance was so high that the "controlled current" source was no longer able to supply the expected current because its compliance voltage (i.e. the maximum voltage which the current source can provide) was insufficient to drive the "fixed" current in the test circuit. The present invention solves that problem by including in the system one or more components which (a) monitor the current in the test circuit, and (b) prevent the delivery of information if the current falls below the "fixed" value.
It can also be desirable, in a Masia/Reed System including a controlled current source, to prevent the .
~27~25~
_g_ delivery of information when the impedance of the con-nection is within some predetermined range ~e.g. above some predetermined level), even when part or all of that predetermined range is not such as to cause the current in the test circuit to fall below the "fixed"
level. Under these circumstances, the information will be correct, but unwanted, and in accordance with the present invention, the system is modified to include one or more components which (a) monitor the output voltage of the current source (the voltage required to deliver the "fixed" current to a particular test circuit) and (b) prevent delivery of information if the output voltage is within a predetermined range.
Similarly, when a constant voltage source is used in the Masia/~eed system it may be desirable to prevent the delivery of information when the impedance of the connection is within some predetermined range (e.g.
above a certain level or below a certain level). Under these circumstances, too, the information will be correct, but unwanted, and in accordance with the pre-sent invention, the system is modified to include one or more components which (a) monitor the current in the test circuit; and (b) prevent delivery of information if tbe current is within a predetermined range.
~;~7~2~;4 In one aspect, the invention provides a method for monitoring for the occurrence of an event which is expected to occur at some unknown time in the future, and for detecting and obtaining information about the event upon its occurrence, which method comprises (1) providing a system (a) which comprises an elongate electrically conductive locating member and an elongate electricall~ conductive source member, and (b) in whlch, 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 (a) the connection, (b~ that part of the locating member between the flrst point and a second point having a known location on the locating member, and (c) a power source which has an output voltage of V volts and which causes an electrical current I amps of known size to be transmitted between the first and second points on the locating member; and the current and the locaiing member being such that, by measuring the voltage drop between the first and ` 10 9~.Z~ i4 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;
(3) when it is determined that a said connection has been made, determining whether the value of the ratio V/I is within a predetermined range, and if it is, measuring the voltage drop between the first and second points; and (4) obtaining information concerning the event from the voltage drop measured in step (3).
Step (4) is preferably carried automatically and the information obtained is fed to a display.
In another aspect the invention provides apparatus which is suitable for use in the method defined above and which comprises (1) a first terminal;
(2) a second terminal;
(3) a third terminal;
(4) means for connecting the first and second terminals to a power source;
Canadian Patent Application Serial No. 478,813 filed on April 11, 1985 in the name of Raychem Corporation describes a ~ystem which is somewhat similar to that referred to in the pre-vious paragraph, but differs from it in that (a) the source mem-ber is connected to the locating member, so that current can pass through the locating member in the absence of an event, and, (b) upon occurrence of the event, electrical connection is made between the locating member and the return member. Thus Canadian application 478,813 provides a novel method for monitoring for the occurrence of an event, and for detecting and obtaining informa-tion about the event upon its occurrence, which :
lZ7~Z54 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 return member;
the connection to the locating member being effective at a first point whose location is defined by at least one characteristic of the event;
the making of the connection enabling the formation of a test circuit which comprises (a) the connection, (b) that part of the locating member which lies between the first point and a second point having a known location on the locating member, and (c) a voltage-measuring device which has an impedance which is very high by comparison with any unknown part of the impedance of the other components of the test circuit;
~2) there is provided a reference circuit which comprises (a) a source member which is electrically connected to the second point on the locating member and to a point on the locating member whose distance from the second point is at least as great as the distance from the second point to the first point, both distances being measured along the locating member, and which is otherwise electrically insulated from the locating member, ~Z762~4 (b) that part of the locating member which lies between the first and second points, and (c) a power source which causes an electrical current of known size to be transmitted between the first and second points on the locating member; the cur-rent 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;
(3) the voltage-measuring device is used to measure the voltage drop between the first and second points; and (4) information concerning the event is obtained from the measurement made in step (3).
Canadian Patent Application Serial No. 468,974 filed on November 29, 1984 in the name of Raychem Corporation describes preferred ways of assembling the locating, return and source members, at least one of the members having a wrapped configura-tion.
Canadian Patent Application Serial No. 478,817 filed on April 11, 1985 in the name of Raychem Corporation describes a modification of the systems of Canadian applications 457,882 and 478,813 in which a reference impedance is placed in series with the locating member, and the location of the first point on the locating member is determined from the ratio of the voltage drops down the locating member and the reference impedance.
!l ~276254 Canadian Patent Application Serial No. 478,819 filed on April 11, 1985 in the name of Raychem Corporation discloses a modification of the systems of Canadian applications 457,882 and 478,813 in which the locating member comprises (a) a plurality of spaced-apart discrete impedant components, each of which has substantial impedance, and (b) a plurality of elongate intermediate components, each of which physically separates and elec-trically connects a pair of impedant components.
When such a locating member is used, the system isarranged 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 com-ponents.
Canadian Patent Application Serial No. 478,818 filed on April 11, 1985 in the name of Raychem Corporation discloses a modification of the system of Canadian application 457,882 in which the system is so arranged that the only variable impedance in the test circuit is the impedance of the connection between the source and locating members.
~2762~;4 In the systems described in the aforementioned applica-tions, a key requirement is that a current of known size is driven down the locating member. In order to supply such a current, a controlled current source is preferably employed.
SUMMARY OF THE I~VE~TIO~
In making use of systems as described in Canadian application Serial No. 457,882, using a controlled current source, delivering a "fixed" current, in order to detect the presence of electrolytes, we found that false information was sometimes obtained. We further discovered that this false information was obtained when a very small amount of electrolyte was present, so that the locating and source members were connected to each other through a connection whose resistance was so high that the "controlled current" source was no longer able to supply the expected current because its compliance voltage (i.e. the maximum voltage which the current source can provide) was insufficient to drive the "fixed" current in the test circuit. The present invention solves that problem by including in the system one or more components which (a) monitor the current in the test circuit, and (b) prevent the delivery of information if the current falls below the "fixed" value.
It can also be desirable, in a Masia/Reed System including a controlled current source, to prevent the .
~27~25~
_g_ delivery of information when the impedance of the con-nection is within some predetermined range ~e.g. above some predetermined level), even when part or all of that predetermined range is not such as to cause the current in the test circuit to fall below the "fixed"
level. Under these circumstances, the information will be correct, but unwanted, and in accordance with the present invention, the system is modified to include one or more components which (a) monitor the output voltage of the current source (the voltage required to deliver the "fixed" current to a particular test circuit) and (b) prevent delivery of information if the output voltage is within a predetermined range.
Similarly, when a constant voltage source is used in the Masia/~eed system it may be desirable to prevent the delivery of information when the impedance of the connection is within some predetermined range (e.g.
above a certain level or below a certain level). Under these circumstances, too, the information will be correct, but unwanted, and in accordance with the pre-sent invention, the system is modified to include one or more components which (a) monitor the current in the test circuit; and (b) prevent delivery of information if tbe current is within a predetermined range.
~;~7~2~;4 In one aspect, the invention provides a method for monitoring for the occurrence of an event which is expected to occur at some unknown time in the future, and for detecting and obtaining information about the event upon its occurrence, which method comprises (1) providing a system (a) which comprises an elongate electrically conductive locating member and an elongate electricall~ conductive source member, and (b) in whlch, 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 (a) the connection, (b~ that part of the locating member between the flrst point and a second point having a known location on the locating member, and (c) a power source which has an output voltage of V volts and which causes an electrical current I amps of known size to be transmitted between the first and second points on the locating member; and the current and the locaiing member being such that, by measuring the voltage drop between the first and ` 10 9~.Z~ i4 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;
(3) when it is determined that a said connection has been made, determining whether the value of the ratio V/I is within a predetermined range, and if it is, measuring the voltage drop between the first and second points; and (4) obtaining information concerning the event from the voltage drop measured in step (3).
Step (4) is preferably carried automatically and the information obtained is fed to a display.
In another aspect the invention provides apparatus which is suitable for use in the method defined above and which comprises (1) a first terminal;
(2) a second terminal;
(3) a third terminal;
(4) means for connecting the first and second terminals to a power source;
(5) a voltage-measuring device for measuring the voltage drop between the second and third terminals;
(6) a display unit for displaying information derived from a voltage drop measured by the voltage-measuring device; and ~.27G2S4 (7) 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 lla ~27G2~;4 a source member, thus forming a test circuit, prevents the display unit from displaying information if the value of the ratio V/I is outside a predetermined range, where I is the current in the test circuit in amps and v is the output voltage of the power source.
~ his apparatus will often comprise a support member to which components (1) to (7) are secured, and/or a housing which provides physical and/or electrical protection for the components.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention is illustrated in the accompanying drawings in which Figures 1, 2 and 3 are schematic cir-cuit diagrams of the method of the invention.
DETAILED DESCRIPTION OF THE INVENTION
As previously noted, a key feature of the earlier Masia/Reed applications is that, upon occurrence of an event, a current of known size is driven down the locating member. When using a fixed current source, as is preferred, it is assumed, in calculating the loca-tion of the first point, that the current driven down the locating member is the "fixed" current. However, this assumption will not be correct if the impedance of the test circuit is so high that the compliance voltage of the current source is insufficient to drive the n fixed" current, and as a result, the location of the first point will not be correct when it is calculated ~Z7~254 from the voltage drop between the first and second points.
The impedance of the test circuit, as defined by Masia/Reed, includes as variables the resistance (RL) of that part of the locating member which lies between the first and second points on the locating member, and the resistance (RE) of the event- sensitive connection means. RL is a variable because the first point can occur anywhere along the locating member, but the upper limit of RL is fixed. RE is a variable because different events typically produce connections having different resistance, and the variation can be very large.
If RL and RE are the only variables in the test circuit, then it is not possible to fix precisely the range of values of RE for which information is obtained. In other words, the sensitivity of the system depends on the location of the first point. This sensitivity decreases as the ratio of RE to the total resistance of the locating member increases. Accordingly, the critical impedance of the connection (or the lowest value if it i8 a range) is generally at least 2 times, preferably at least 5 times, particularly at least 10 times, the impedance of the full length of the locating member.
By making use of the invention described in Canadian Patent application Serial No. 478,818, the values of RE can be fixed precisely. Thus Reeder's systems include in the test cir-cuit a component which (1) is connected in series with that part of the locating member which ~Z7~2~4 lies between the first and second points and (2) has an impedance substantially equal to the difference between the total impedance of the locating member and the impedance of that part of the locating member. Such a component is preferably provided by making use of a source member which has the same impedance charac-teristics as the locating member.
The range of values for the ratio V/I within which information will be reported can easily be changed (for example so that leaks of different minimum sizes are signalled). When using a fixed current source, sen-~itivity 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 the preselected range of output voltages. When using a fixed 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.
By way of example, in a system in which (1) the source and locating members have a diameter of 30 mils, are separated by a distance of 0.25 inch, and are assembled in a braided configuration; and (2) the "fixed~ current is 250 microamps, then, if RE is set at 16.5 kilohms, a water leak less than 2 inches in length is ignored by the system and a water leak in excess of 2 inches in length is detected by the system.
Attention is now directed to Figures 1, 2 and 3 which show schematic circuit diagrams of the method of the present invention.
~27G2~;~
Figure 1 includes a system 10 comprising source, S, locating, L, and return, R, terminals. The source terminal receives input along a line 12 from a power supply 14, shown as a controlled current supply. The locating and return terminals are connected along lines 16 and 18 respectively to a display 20. An overrange blanking unit 22 is connected along lines 24 and 26 to the power supply line 12 and display 20.
The overrange blanking unit 22 continuously moni-tors the output voltage of the controlled current source ~see Figure 2). If the variable sum (RL+RE) exceeds a predetermined value, so as to increase the output voltage to the compliance voltage, then the overrange blanking unit 22 blanks out the display 20 so that it will not display incorrect information as to event location.
Figure 3 is similiar to Figure 2 except that the power supply 14 is a constant voltage source. The variable current in the test circuit, ILoop~ is moni-tored by an ammeter A. If the ammeter indicates that ILoop has fallen below a predetermined size, then the overrange blanking unit 22 blanks out the display 20.
~ his apparatus will often comprise a support member to which components (1) to (7) are secured, and/or a housing which provides physical and/or electrical protection for the components.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention is illustrated in the accompanying drawings in which Figures 1, 2 and 3 are schematic cir-cuit diagrams of the method of the invention.
DETAILED DESCRIPTION OF THE INVENTION
As previously noted, a key feature of the earlier Masia/Reed applications is that, upon occurrence of an event, a current of known size is driven down the locating member. When using a fixed current source, as is preferred, it is assumed, in calculating the loca-tion of the first point, that the current driven down the locating member is the "fixed" current. However, this assumption will not be correct if the impedance of the test circuit is so high that the compliance voltage of the current source is insufficient to drive the n fixed" current, and as a result, the location of the first point will not be correct when it is calculated ~Z7~254 from the voltage drop between the first and second points.
The impedance of the test circuit, as defined by Masia/Reed, includes as variables the resistance (RL) of that part of the locating member which lies between the first and second points on the locating member, and the resistance (RE) of the event- sensitive connection means. RL is a variable because the first point can occur anywhere along the locating member, but the upper limit of RL is fixed. RE is a variable because different events typically produce connections having different resistance, and the variation can be very large.
If RL and RE are the only variables in the test circuit, then it is not possible to fix precisely the range of values of RE for which information is obtained. In other words, the sensitivity of the system depends on the location of the first point. This sensitivity decreases as the ratio of RE to the total resistance of the locating member increases. Accordingly, the critical impedance of the connection (or the lowest value if it i8 a range) is generally at least 2 times, preferably at least 5 times, particularly at least 10 times, the impedance of the full length of the locating member.
By making use of the invention described in Canadian Patent application Serial No. 478,818, the values of RE can be fixed precisely. Thus Reeder's systems include in the test cir-cuit a component which (1) is connected in series with that part of the locating member which ~Z7~2~4 lies between the first and second points and (2) has an impedance substantially equal to the difference between the total impedance of the locating member and the impedance of that part of the locating member. Such a component is preferably provided by making use of a source member which has the same impedance charac-teristics as the locating member.
The range of values for the ratio V/I within which information will be reported can easily be changed (for example so that leaks of different minimum sizes are signalled). When using a fixed current source, sen-~itivity 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 the preselected range of output voltages. When using a fixed 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.
By way of example, in a system in which (1) the source and locating members have a diameter of 30 mils, are separated by a distance of 0.25 inch, and are assembled in a braided configuration; and (2) the "fixed~ current is 250 microamps, then, if RE is set at 16.5 kilohms, a water leak less than 2 inches in length is ignored by the system and a water leak in excess of 2 inches in length is detected by the system.
Attention is now directed to Figures 1, 2 and 3 which show schematic circuit diagrams of the method of the present invention.
~27G2~;~
Figure 1 includes a system 10 comprising source, S, locating, L, and return, R, terminals. The source terminal receives input along a line 12 from a power supply 14, shown as a controlled current supply. The locating and return terminals are connected along lines 16 and 18 respectively to a display 20. An overrange blanking unit 22 is connected along lines 24 and 26 to the power supply line 12 and display 20.
The overrange blanking unit 22 continuously moni-tors the output voltage of the controlled current source ~see Figure 2). If the variable sum (RL+RE) exceeds a predetermined value, so as to increase the output voltage to the compliance voltage, then the overrange blanking unit 22 blanks out the display 20 so that it will not display incorrect information as to event location.
Figure 3 is similiar to Figure 2 except that the power supply 14 is a constant voltage source. The variable current in the test circuit, ILoop~ is moni-tored by an ammeter A. If the ammeter indicates that ILoop has fallen below a predetermined size, then the overrange blanking unit 22 blanks out the display 20.
Claims (13)
1. A method for monitoring for the occurrence of an event which is expected to occur at some unknown time in the future, and for detecting and obtaining information about the event upon its occurrence, which method comprises (1) providing a system (a) which comprises an elongate electrically conductive locating member and an elongate electrically conductive source member, 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 effec-tive at a first point whose location is defined by at least one characteristic of the event;
the making of the connection enabling the for-mation of a test circuit which comprises (a) the connection, (b) that part of the locating member between the first point and a second point having a known location on the locating member, and (c) a power source which has an output voltage of V
volts and which causes an electrical current I
amps 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;
(3) when it is determined that a said connection has been made, determining whether the value of the ratio V/I is within a predetermined range, and if it is, measuring the voltage drop between the first and second points; and (4) obtaining information concerning the event from the voltage drop measured in step (3).
the making of the connection enabling the for-mation of a test circuit which comprises (a) the connection, (b) that part of the locating member between the first point and a second point having a known location on the locating member, and (c) a power source which has an output voltage of V
volts and which causes an electrical current I
amps 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;
(3) when it is determined that a said connection has been made, determining whether the value of the ratio V/I is within a predetermined range, and if it is, measuring the voltage drop between the first and second points; and (4) obtaining information concerning the event from the voltage drop measured in step (3).
2. A method according to claim 1, wherein the power source is a controlled current source which delivers a known fixed current until its output voltage exceeds its compliance voltage.
3. A method according to claim 1 or 2, wherein the information obtained in step (4) is provided to a display.
4. A method according to claim 1 or 2, which comprises monitoring the current in the test circuit and preventing the display of information when the current falls below the fixed current.
5. A method according to claim 1 or 2, which comprises monitoring the output voltage of said current source, and preventing the display of information if the output voltage falls outside a predetermined range.
6. A method according to claim 1, wherein the power source is a constant voltage source and information obtained in step (4) is provided to a display, comprising the steps of (a) monitoring the current in the test circuit; and (b) blanking out the display if the current in the test circuit falls outside a predetermined range.
7. A method according to claim 1 or 2 , comprising adjusting the sensitivity of the system by changing the compliance voltage of the current source or inserting a resistance of known value in the test circuit.
8. A method according to claim 1, 2 or 6, wherein the value of the ratio V/I is below a predetermined value which is selected so that information concerning the event is not obtained if the resistance of the connec-tion between the locating and source members has a pre-determined value which is at least 10 times the resistance of the full length of the locating member.
9. Apparatus which is suitable for use in a method as defined in claim 1 and which comprises (1) a first terminal;
(2) a second terminal;
(3) a third terminal;
(4) means for connecting the first and second terminals to a power source;
(5) a voltage-measuring device for measuring the voltage drop between the second and third terminals;
(6) a display unit for displaying information derived from a voltage drop measured by the voltage-measuring device; and (7) 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/I is outside a predetermined range, where I is the current in the test circuit in amps and V is the output voltage of the power source in volts.
(2) a second terminal;
(3) a third terminal;
(4) means for connecting the first and second terminals to a power source;
(5) a voltage-measuring device for measuring the voltage drop between the second and third terminals;
(6) a display unit for displaying information derived from a voltage drop measured by the voltage-measuring device; and (7) 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/I is outside a predetermined range, where I is the current in the test circuit in amps and V is the output voltage of the power source in volts.
10. Apparatus according to claim 9 which is adapted to be connected to a fixed voltage AC power source and which comprises a constant current source which con-verts the AC input into a DC current of controlled size.
11. Apparatus according to claim 9 or 10 wherein the device (7) is a current-sensitive device which prevents the display of information if the current in the test circuit falls below a controlled size.
12. Apparatus according to claim 9 or 10 wherein the device (7) is a voltmeter which monitors the output voltage of the constant current source.
13. Apparatus according to claim 9 which is adapted to be connected to a fixed voltage AC power source and to supply power to the test circuit at a fixed voltage, and wherein the device (7) is a current-sensitive device.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US60348584A | 1984-04-24 | 1984-04-24 | |
| US603,485 | 1984-04-24 | ||
| US61810884A | 1984-06-07 | 1984-06-07 | |
| US618,108 | 1984-06-07 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1276254C true CA1276254C (en) | 1990-11-13 |
Family
ID=27084443
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000478820A Expired - Lifetime CA1276254C (en) | 1984-04-24 | 1985-04-11 | Method for detecting and obtaining information about changes in variables |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1276254C (en) |
-
1985
- 1985-04-11 CA CA000478820A patent/CA1276254C/en not_active Expired - Lifetime
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