Method and apparatus for detecting and locating fluid leaks

• US 4,083,229 A
• Filed: 09/28/1976
• Issued: 04/11/1978
• Est. Priority Date: 09/28/1976
• Status: Expired due to Term

• Current Assignee: Plaunt & Anderson Company Incorporated
• Original Assignee: Plaunt & Anderson Company Incorporated
• Inventors: Anway, Allen R.
• Primary Examiner(s): Woodiel, Donald O.
• Application Number:
  US05/727,359
• Time in Patent Office: 560 Days
• Field of Search: 73/40.5 A, 73/40.5 R, 73/71.2
• US Class Current: 73/40.50A
• CPC Class Codes: G01M 3/243 for pipes

Abstract

An apparatus and method for detecting and locating a fluid leak in an underground pipe or the like in which the vibration produced by the leak is intercepted at selected spaced apart points by microphones or other transducers, in which the vibration intercepted at each of the two points is converted into an electrical signal, and in which the extent of correlation of the two resulting signals is varied by variably time delaying one signal relative to the other to determine the leak'"'"'s location from the occurrence of maximum correlation between the signals. In one embodiment, the variable time delay of one signal relative to the other is accomplished by a variable length time delay line and a means for progressively varying the length of the delay line. In another embodiment the variable time delay is accomplished by a recirculating delay line analyzer that does more data age comparisons with the same delays in the same time than the variable length delay line.

Claims

1. In an apparatus for locating a fluid leak in an underground or unexposed pipe or conduit, first means effective upon receipt of a vibration caused by the leak for producing an electrical signal corresponding in phase and frequency to the received vibration, second means effective upon receipt of the vibration for producing a further electrical signal corresponding in phase and frequency to the received vibration, electrical time delay circuit means electrically connected to said first means for variably time delaying one of said electrical signals relative to the other to cause maximum mutual time correlation between the two signals, and means providing an indication of the time correlation between the time delayed one of said signals and the other of said electrical signals.

2. The apparatus defined in claim 1 wherein said electrical time delay circuit means comprises a recirculating time delay line.

3. The apparatus defined in claim 1 wherein said electrical time delay circuit means comprises a variable length, non-recirculating time delay line.

4. In an apparatus for locating a fluid leak in an underground or unexposed pipe, first means for intercepting a vibration produced by the leak at two spaced apart points and for converting the vibration intercepted at each of said points into an electrical signal to provide two electrical signals that are miscorrelated in time to an extent determined by the location of the leak from said points, an electrical circuit electrically connected to said first means and including time delay means for varying the extend of time correlation between at least samples of said two signals to cause maximum time correlation therebetween and means providing an indication of the variation of the extent of time correlation between the samples to enable the leak'"'"'s location to be determined from the occurrence of the maximum time correlation.

5. The apparatus defined in claim 4 wherein said first means comprises a pair of stationarily positioned microphones adapted to be located one at each of said interception points to intercept said vibration.

6. The apparatus defined in claim 4 wherein said interception points are selectively located along the path of said pipe, and wherein said first means comprises a pair of microphones adapted to be located one at each of said interception points.

7. The apparatus defined in claim 4 wherein said time delay means comprises a time delay line for variably time delaying at least samples of one said signals relative to the other.

8. The apparatus defined in claim 4 wherein said time delay means comprises a recirculating time delay line for variably time delaying at least samples of one of said signals relative to the other.

9. The apparatus defined in claim 4 wherein said signals are digital signals and wherein said time delay means comprises a recirculating time delay line for variably time delaying samples of one of said signals relative to samples of the other of said signals, means for periodically entering samples of said one of said signals into said delay line at a first predetermined rate, and means for recirculating the samples in said delay line at a rate that is faster than said first predetermined rate.

10. The apparatus defined in claim 4 wherein said signals are digital signals, and wherein said time delay means comprises a first circulating shift register for variably time delaying samples of one of said signals relative to the other, means for periodically entering samples of said one of said signals into said first register at a first predetermined rate, means for circulating the contents in said first register at a second predetermined rate that is faster than said first predetermined rate, and a second circulating shift register for delaying samples of the other of said signals, said second shift register being clocked to circulate the samples of said other of said signals at said first predetermined rate, and said second register having a bit length that is shorter than that of said first register.

11. The apparatus defined in claim 4 wherein said time delay means comprises a variable length delay line for variably delaying at least samples of one of said signals relative to the other, and means for progressively varying the length of said delay line to cause the variation in the extent of correlation between the signals.

12. The apparatus defined in claim 11 wherein said electrical circuit comprises a further delay line of fixed, pre-selected length for delaying at least samples of the other of said signals.

13. In an apparatus for locating a fluid leak in an underground or unexposed pipe, first means for intercepting a sound wave produced by the leak at two separate points spaced apart along the path of the pipe and for producing two electrical signals having a phase difference which is related to the difference in time required for the wave to propagate to the interception points, said first means having a pair of microphones adapted to be positioned one at each of said interception points to intercept said sound wave, an electrical circuit connected to said first means and including time delay means for progressively phase shifting at least one of said signals to cause at least momentarily maximum mutual phase correlation between the two signals, means providing an indication which is a function of the degree of mutual phase correlation between the phase shifted signal and the other of said signals as said one of said signals is progressively phase shifted to indicate the occurrence of maximum mutual phase correlation between the two signals, and means providing a measurement which is a function of the distance of the leak from a known predetermined point at the time maximum mutual phase correlation occurs when the leak is located between the two microphones or at either one of the microphones.

14. The apparatus defined in claim 13 wherein said electrical circuit further includes selectively adjustable delay means for delaying the other of said signals by a fixed selected amount.

15. In an apparatus for locating fluid leak in an underground or unexposed pipe, first and second transducers adapted to be positioned at spaced apart regions along the path of the pipe to intercept a vibration produced by the leak and propagating along the pipe, each of said transducers being effective to convert the intercepted vibration into an electric wave, a circuit for modifying the electric waves produced by said transducers into first and second pulse signals having a phase difference which is related to the location of the leak from said transducers, means in said circuit for progressively phase shifting one of said pulse signals relative to the other pulse signal to cause at least momentarily maximum mutual phase correlation between said first and second pulse signals, means electrically connected to said circuit for producing a further pulse signal which is a measure of the degree of mutual phase correlation between the phase shifted pulse signal and other pulse signal, and means controlled by said further pulse signal for providing an indication which is a function of the degree of mutual phase correlation between the phase shifted pulse signal and said other pulse signal to indicate the occurrence of maximum mutual phase correlation between the phase shifted pulse signal and the other pulse signal.

16. The apparatus defined in claim 15 comprising means providing a distance measurement which is a function of the location of the leak from a known predetermined point at the time maximum mutual phase correlation occurs between the phase shifted pulse signal and the other of said first and second pulse signals.

17. In an apparatus for locating a fluid leak in an underground or unexposed pipe, first means for intercepting a vibration produced by the leak at two spaced apart points and for converting the intercepted vibration into first and second electrical signals having a phase difference which is function of the difference in time required for the vibration to propagate to said points, selectively operable switching means electrically connected to said first means, a variable time delay line electrically connected to said switching means, a phase correlation measuring means electrically connected to said time delay line and to said switching means, said switching means having a first switching position in which it feeds said first signal to said time delay line and in which it bypasses said second signal around said time delay line and feeds the second signal to said measuring means, said switching means having a second switching position in which it feeds said second signal to said time delay line and in which it bypasses said first signal around said delay line and feeds the first signal to said measuring means, means for varying the delay of said delay line to delay the signal fed to the delay line by said switching means, and said measuring means being effective to produce a further signal which is a function of the extent of phase correlation between the delayed signal from said delay line and the other signal which is bypassed around said delay line by said switching means.

18. In an apparatus for locating a fluid leak in an underground or unexposed pipe, first and second circuits each having (a) a microphone for intercepting the vibration produced by the leak to produce an a.c. signal, and (b) a polarity detector for detecting each alternation of one preselected polarity of said signal to produce a pulse wave form, at least one of said first and second circuits having a time delay line for delaying the pulse wave form developed by the polarity detector in one of said circuits relative to the pulse wave form developed by the polarity detector in the other of said first and second circuits, means for varying the delay of said delay line over a pre-selected range, and phase correlation measuring means electrically connected to said first and second circuits for producing a signal which is a function of the phase difference between the pulse wave form which is delayed by said delay line and the pulse wave form developed in said other of said first and second circuits.

19. In an apparatus for locating a fluid leak in an underground or unexposed pipe, means for intercepting a vibration produced by the leak at two selected points that are spaced apart along the path of said pipe and for converting the vibration intercepted at each of said points into an electrical digital signal to provide two signals that are miscorrelated to an extent determined by the location of the leak from said points, means variably time delaying one of the signals relative to the other of said signals for varying the extent of correlation between said signals to achieve maximum correlation between the signals, and means for displaying the variations of the extent of correlations between the time delayed signal and the other of said signals to enable the location of the leak to be determined from the place at which the maximum correlation occurs.

20. The apparatus defined in claim 19 wherein said means for time delaying said one of said signals comprises a recirculating delay line.

21. The apparatus defined in claim 19 wherein said means for time delaying said one of said signals comprises a variable length time delay line and means for incrementally and progressively varying the length of said delay line.

22. In an apparatus for locating a fluid leak in an underground or unexposed pipe, means for intercepting a vibration produced by said leak at two selected points that are spaced apart along the path of said pipe and for converting the vibration intercepted at each of said points into a digital signal to provide two digital signals that are related in phase to the location of the leak from said points, a circulating time delay line for time delaying samples of one of said signals relative to the other, a correlator for comparing the time delayed samples of said one of said signals with at least samples of the other of said signals, and means responsive to the output of said correlator for enabling the location of said leak to be established.

23. The apparatus defined in claim 22 wherein said time delay line comprises a circulating shift register, and means for periodically entering samples of said one of said signals into said shift register at a rate that is slower than the rate at which the samples are recirculated by said shift register.

24. The apparatus defined in claim 22 wherein said signal samples are in the form of binary bits and wherein said correlator comprises a logic gate that produces a binary output of one logic state when the compared signal samples have the same logic state and a binary output of the other logic state when the logic states of the compared signal samples are not the same.

25. The apparatus defined in claim 24 wherein said delay line non-progressively variably delays samples of said one of said signals in a scrambled, but predetermined order, and wherein said means responsive to the output of said correlator comprises a memory having a multiplicity of addresses for storing binary data, means for addressing said memory for storing data determined by the output of said logic gate at addresses in the memory that are determined by the time delays of the samples of said first signal relative to the samples of said second signal, and means for reading the data out of said memory in a predetermined order that is different from the order in which the data is written into the memory.

26. In an apparatus for locating a fluid leak in an underground or unexposed pipe, means for intercepting a vibration produced by the leak at two selected points that are spaced apart along the path of said pipe and for converting the vibration intercepted at said points into two digital signals that are related to the location of the leak from said interception points, means for variably time delaying one of said signals relative to the other to vary the extent of correlation between the two signals, and means for indicating the varied extent of correlation to provide an indication of the location of the leak.

27. The apparatus defined in claim 26 wherein said means for variably time delaying said one of said signals comprises a circulating time delay line and means for circulating samples of said one signal through said delay line at a rate that is faster than the rate at which samples of said one signal are entered into said delay line.

28. An apparatus for locating a fluid leak in an underground or unexposed pipe comprising means for intercepting a vibration produced by the leak at two selected points that are spaced apart along the path of the pipe and for converting the vibration intercepted at said points into two digital signals that are related in phase to the location of the leak from said points, and means for scanning at least a portion of said pipe between said points for the location of said leak by variably time delaying samples of one of said signals relative to samples of the other of said signals.

29. The apparatus defined in claim 28 wherein said scanning means scans spaced apart locations of said pipe portion for said leak, and wherein means are provided for selectively adjusting the scanning resolution of said scanning means.

30. A method of locating a fluid leak in an underground or unexposed pipe comprising the steps of intercepting the vibration produced by the leak at two spaced apart points and converting the vibration intercepted at each of said points into an electrical signal to provide two electrical signals that are miscorrelated in time to an extent determined by the location of the leak from said points, electrically processing at least one of said signals by varying the extent of time correlation between the two signals to cause maximum time correlation between the signals, and determining the location of the leak from the occurrence of said maximum correlation.

31. A method of locating a fluid leak in an underground or unexposed pipe comprising the steps of intercepting the vibration produced by the leak at two selected points spaced apart along the path of the pipe and converting the vibration intercepted at each of said points into an electrical signal to provide two electrical signals that are miscorrelated in time to an extent determined by the location of the leak from said points, electrically processing at least one of said two signals by variably time delaying one of said signals relative to the other without changing the selected points at which the vibration is intercepted to vary the extent of time correlation between the signals, and determining the location of the leak from the variation of the extent of time correlation between the signals.

32. The method defined in claim 31 comprising the step of locating said interception points on opposite sides of the suspected site of the leak.

33. The method defined in claim 32 comprising the step of time delaying the other of said signals by a fixed selected amount during the course of variably time delaying said one of said signals.

34. The method defined in claim 33 comprising the step of time delaying the other of said signals during the course of variably delaying by a fixed time equal to the time required for said vibration to propagate the length of the pipe between the two interception points.

35. The method defined in claim 32 comprising the step of imparting no delay to the other of said signals.

36. In an apparatus for locating a fluid leak in an underground or unexposed pipe, first means including a pair of transducers for intercepting a vibration produced by the leak at two selected points that are spaced apart along the path of said pipe and for converting the vibration intercepted at each of said points into a digital signal to provide two digital signals that are miscorrelated to an extent determined by the location of the leak from said points, a recirculating time delay line, means for electrically connecting said delay line to a part of said first means and for entering digital bits of one of said signals into said delay line at a first predetermined rate, means for circulating the digital bits entered into said delay line at a second predetermined rate to variably time delay the bits of said one of said signals relative to digital bits of the other of said signals and to thereby vary the extent of correlation between the bits of said one of said signals and the bits of the other of said signals to achieve maximum correlation between the bits of said one of said signals and the bits of the other of said signals, said second predetermined rate being faster than said first predetermined rate, and means providing a read-out of the variations of the extent of correlation between the bits of said one of said signals and the bits of said other of said signals to enable the location of the leak to be determined from the occurrence of the maximum correlation between the bits of said one of said signals and the bits of the other of said signals.

37. In an apparatus for locating a fluid leak in an underground or unexposed pipe, first means including a pair of transducers for intercepting a vibration produced by the leak at two selected points that are spaced apart along the path of said pipe and for converting the vibration intercepted at each of said points into a digital signal to provide two digital signals that are miscorrelated to an extent determined by the location of the leak from said points, a recirculating shift register having a pre-selected bit length, means electrically connecting said shift register to a part of said first means for entering digital bits of one of said signals into said shift register every time the shift register completes a pre-selected number of shifts, where said pre-selected number of shifts and said pre-selected bit length of said shift register have no common factors to enable said shift register to be filled up with digital signal bits of different relative ages, means for circulating the bits entered to said shift register at a predetermined rate to variably time delay the bits of said one of said signals relative to digital bits of the other of said signals and to thereby vary the extent of correlation between the bits of said one of said signals and the bits of the other of said signals to achieve maximum correlation between the bits of said one of said signals and the bits of the other of said signals, said predetermined rate being faster than the rate at which bits of said one of said signals is entered into said shift register, and means providing a read-out of the variations of the extent of correlation between the bits of said one of said signals and the bits of said other of said signals to enable the location of the leak to be determined from the occurrence of the maximum correlation between the bits of said one of said signals and the bits of the other of said signals.

38. In an apparatus for locating a fluid leak in an underground or unexposed pipe, first and second circuits each having (a) a microphone for intercepting the vibration produced by the leak to produce a first a.c. signal, (b) an envelope detector responsive to said first a.c. signal for developing a further a.c. signal which follows the envelope of said first a.c. signal and (c) a polarity detector for detecting each alternation of one pre-selected polarity of said further signal to produce a pulse wave form, at least one of said first and second circuits having a time delay line for variably time delaying the pulse wave form developed by the polarity detector in one of said circuits relative to the pulse wave form developed by the polarity detector in the other of said first and second circuits to vary the extent of correlation between the pulse wave forms and means for indicating the variation of the extent of correlation between the pulse wave forms to enable the location of the leak to be determined from the occurrence of maximum correlation between the two pulse wave forms.

39. A data analyzing and storage apparatus comprising a logic gate having an output and a plurality of inputs, means providing a first data channel for feeding binary data bits in order of their relative ages to a first input of said gate, means providing a second data channel for supplying binary data bits to a second input of said gate, means including a circulating delay line in said second channel for variably time delaying the data bits in second channel relative to the data bits fed through said first channel to scramble the relative ages of the data bits that are fed from said second channel to said second input of said gate, the binary state of the output of said gate being determined by the states of the binary bits fed to said first and second inputs, a memory having a multiplicity of addressable locations for storing binary data, and means for addressing said locations in a first predetermined order for writing in binary data that is determined by the output of said logic gate and further for addressing said locations in said second predetermined order for reading out the stored data, said second predetermined order being different from said first predetermined order and providing for a read-out of the stored data in an order than has pre-selected relationship to the age differences between the binary bits fed to the inputs of said gate.

40. The data analyzing and storage apparatus defined in claim 39 wherein said logic gate is a correlator.

41. An apparatus for locating a fluid leak in an underground or unexposed pipe or conduit, said apparatus comprising first means effective upon receipt of a vibration caused by the leak for producing an electrical digital signal corresponding in phase and frequency to the received vibration, second means effective upon receipt of the vibration for producing a further electrical digital signal corresponding in phase and frequency to the received vibration, electrical circuit means for variably time delaying one of said electrical signals relative to the other to cause maximum mutual correlation between the two signals, and means providing an indication of the correlation between the time delayed signal and the other signal, said electrical circuit means comprising a recirculating time delay line.

42. An apparatus for locating a fluid leak in an underground or unexposed pipe or conduit, said apparatus comprising first means effective upon receipt of a vibration caused by the leak and producing an electrical digital signal corresponding in phase and frequency to the received vibration, second means effective upon receipt of the vibration for producing a further electrical digital signal corresponding in phase and frequency to the received vibration, electrical circuit means for variably time delaying one of said electrical signals relative to the other to cause maximum mutual correlation between the two signals, and means providing an indication of the correlation between the time delayed signal and the other signal, said electrical circuit means comprising a variable length, nonrecirculating time delay line.

43. An apparatus for locating a fluid leak in an underground or unexposed pipe comprising first and second electrical circuits each having (a) a microphone for intercepting the vibration produced by the leak and (b) means connected to the microphone for producing an electrical digital signal related in phase and frequency to the vibration received by the microphone, said microphones being adapted to be located at two spaced apart points on opposite sides of the leak to cause said signals to be miscorrelated in time to an extent determined by the location of the leak between said points, at least one of said first and second circuits having a time delay line for variably time delaying one of said digital signals relative to the other to cause maximum mutual time correlation between the two signals, and means electrically connected to said first and second circuits and providing an indication of the extent of time correlation between said signals to enable the leak'"'"'s location to be determined from the occurrence of the maximum mutual time correlation between the two signals.