GB2476266A

GB2476266A - Sensor for determining the location of a disturbance comprising a signal conduit which when disturbed creates a signal that propagates to either end

Info

Publication number: GB2476266A
Application number: GB0922043A
Authority: GB
Inventors: Adam Bridgen
Original assignee: Geoquip Ltd
Current assignee: Geoquip Ltd
Priority date: 2009-12-17
Filing date: 2009-12-17
Publication date: 2011-06-22
Anticipated expiration: 2029-12-17
Also published as: GB2476266B; GB0922043D0

Abstract

A sensing apparatus 10 is provided with a signal conduit 12 which has two ends 15. The conduit 12 is operable to create a signal 14 when disturbed between the ends 15, the signal 14 thereafter propagating from the position of the disturbance 16 to each of the ends 15. Further the apparatus 10 has analyser means 18 which is operable to detect the signal 14 as received at each of the ends 15. The analyser means 18 is operable to find the maximal correlation of the signal 14 as received at each of the ends 15, and to determine the position of the disturbance 16 from the maximal correlation. In another aspect, a method is provided for using the apparatus. The signal conduit may include an electrical conductor movable, when disturbed, in a magnetic field to create an electrical signal propagating along the conductor to both ends.

Description

lmrovements in or Relating to Sensing pparatus The present invention relates to sensing apparatus.

In one aspect, the invention provides apparatus comprising: a signal conduit having two ends and operable to create a signal when disturbed between the ends, the signal thereafter propagating from the position of the disturbance to each of the ends; analyser means operable to detect the signal as received at each of the ends; and the analyser means being operable to find the maximal correlation of the signal as received at each of the ends, and to determine the position of the disturbance from the maximal correlation.

The apparatus may further comprise a communication channel operable for communicating the signal received at least at one of the ends, to the analyser means. The communication channel may be provided separately from the signal conduit. Alternatively, the communication channel may be provided in the same structure as the signal conduit. The communication channel may be optical, mechanical, electrical or electromagnetic.

The analyser means may comprise an analyser operable to receive the signals from the respective ends of the signal conduit for correlation of the changes. The analyser means may comprise first and second analysers operable separately to provide initial analysis of the signal received at respective ends of the signal conduit, and the analyser means being operable to combine the results to complete the correlation. The results of the initial analysis by one of the analysers may be forwarded to the other analyser for completion of the correlation.

The analyser means may be operable to detect at least one parameter of the signal as received at each of the ends, the parameter changing as the signal propagates along the signal conduit. The received signals may be correlated to detect a difference in at least one parameter, caused by a difference of path lengths along the signal conduit, thereby to determine the position of the disturbance. The correlation may identify the time separation of corresponding features of the signal as received at each of the ends, to identify differences in propagation delay.

Each of the received signals may be periodically sampled, and the samples combined to complete the correlation. Each of the samples may be allocated a timestamp. The samples representing each of the received signals may be stored, and a correlation value obtained by combining samples of one of the received signals with corresponding samples of the other received signal, and further correlation values are created by changing the correspondence between the samples, to yield a correlation curve. Multiple correlation values may be created, each representing a different time correspondence between the samples. Each correlation value may be calculated as a sum of products of the corresponding samples. Each correlation value may be obtained from all of the samples of the received signals, or subsets of the samples. The subsets may contain contiguous samples.

The apparatus may further comprise buffers operable to store the samples. The analyser may be operable to shift the contents of one buffer relative to those of the other buffer, and to obtain a correlation value at a plurality of shift positions.

Alternatively, the analyser may be operable to change the subset of samples used to obtain a correlation value.

The signal conduit may include an electrical conductor movable, when disturbed, in a magnetic field, to create an electrical signal propagating along the conductor.

In another aspect, the invention provides a method in which: a signal conduit having two ends is used to create a signal when disturbed between the ends, the signal thereafter propagating from the position of the disturbance to each of the ends; the signal is detected as received at each of the ends; and the signal is analysed to find the maximal correlation of the signal as received at each of the ends, and to determine the position of the disturbance from the maximal correlation.

The signal received at least at one of the ends may be communicated to the other end for analysis. A communication channel may be provided separately from the signal conduit. Alternatively, a communication channel may be provided in the same structure as the signal conduit. The communication channel may be optical, mechanical, electrical or electromagnetic.

There may be initial analysis of the signal received at respective ends of the signal conduit, followed by combining the results to complete the correlation.

At least one parameter of the signal as received at each of the ends may be detected, the parameter changing as the signal propagates along the signal conduit. The received signals may be correlated to detect a difference in at least one parameter, caused by a difference of path lengths along the signal conduit, thereby to determine the position of the disturbance. The correlation may identify the time separation of corresponding features of the signal as received at each of the ends, to identify differences in propagation delay.

Each of the received signals may be periodically sampled, and the samples combined to complete the correlation. Each of the samples may be allocated timestamp.

The samples representing each of the received signals may be stored, and a correlation value obtained by combining each sample of one of the received signals with a corresponding sample of the other received signal, and further correlation values are created, by changing the correspondence between the samples, to yield a correlation curve. Multiple correlation values may be created, each representing a different time correspondence between the samples. Each correlation value may be calculated as a sum of products of the corresponding samples. Each correlation may be calculated from all of the samples of the received signals, or from subsets of the samples. The subsets may contain contiguous samples.

The samples may be stored in buffers. The contents of one buffer may be shifted relative to those of the other buffer, for obtaining a further correlation value, and a correlation value being obtained at a plurality of shift positions.

Alternatively each correlation value may be obtained from a different subset of samples.

Various example embodiments of the present invention will now be described in more detail, by way of example only, and with reference to the accompanying drawings, in which: Fig. 1 is a schematic diagram of sensing apparatus; Fig. 2 is a schematic section through a signal conduit of the apparatus of Fig. 1; Fig. 3 is a schematic diagram of the apparatus, including analyser arrangements; Fig. 4 illustrates the analyser arrangements in more detail; and Fig. 5 is a plot of the results of analysis.

Overview Fig. 1 is a simple diagram of one example of apparatus 10. The apparatus 10 comprises a signal conduit 12 in the form of a sensor wire to be described more fully below. The sensor wire 12 has two ends 15 and is operable to create a signal (indicated schematically at 14) when disturbed between the ends 15, at a position such as that indicated at 16. The signal 14 thereafter propagates from the position of the disturbance 16 to each of the ends 15. Analyser means 18 are operable to detect the signal 14 as received at each of the ends 15, and the analyser means 18 is operable to find the maximal correlation of the signal 14 as received at each of the ends 15. The position of the disturbance 16 is determined from the maximal correlation, as will be described.

Sensor wire Fig. 2 is a simplified cross-section through a cable 19 for use in the arrangement of Fig. 1. In this example, the cable 19 includes Iwo core pieces 20 which are magnetised as indicated by the letters "N" and "S'. The core pieces 20 define a relatively large cavity 22 in which the sensor wire 12 is located and is free to move laterally. A relatively small cavity 24 contains a second wire 26, which is fixed in position relative to the core pieces 20. *30

The magnetisation of the core pieces 20 results in magnetic flux within the cavity 22. Accordingly, the sensor wire 12 will move in this magnetic flux, in the event that the cable 19 is disturbed, for example by impact or vibration. This movement of the sensor wire 12 will generate a voltage in the sensor wire 12, resulting in a voltage signal propagating in both directions along the sensor wire 12. Screening against electromagnetic noise may be required.

Many other arrangements could be envisaged for creating an electrical signal frgm a disturbance. One example is described in our previous British patent GB21 75771 B. Other types of signal could be created, such as a vibration.

Overview of analyser arrangements Returning to Fig. 1, the analyser means 18 includes first and second analyser circuits 28, 30 operable to receive the signal 14 from respective ends of the sensor wire 12. In this example, the first and second analysers 28, 30 are operable separately to provide initial analysis of the signal 14 received at the respective ends 15. This initial analysis may simply be a measurement of an instantaneous magnitude of the signal 14. Other example measurements are described below. The analysers 28, 30 can combine the results in order to complete the correlation between the signals 14 received at the respective ends 15, as will be described. This is facilitated by providing a communication channel by which the result of the initial analysis by the second analyser 30 can be forwarded to the first analyser 28, for completion of the correlation operation with the information received by the first analyser 28, directly from the sensor wire 12.

The communication channel may be provided by the second wire 26 in the cable 19, thus being provided in the same structure as the signal conduit or sensor wire 12. Alternatively, the communication channel may be provided separately from the signal conduit as indicated at 32 in Fig. 1. In either of these examples, the communication channel may be optical, mechanical, electrical or other electromagnetic system (such as radio), and may incorporate amplification or other signal processing, if desired.

Thus, in the example illustrated in Fig. 1, the initial analysis by one of the analysers 28, 30 is forwarded to the other analyser for completion of the correlation. Alternatively, the initial analysis results from both of the analysers 28, 30 could be sent to a third device for completion of the correlation, as illustrated in Fig. 3, in which a processor arrangement 34, to be described below, receives information from each of the analysers 28, 30.

In one example, applicable to the structure of either Fig. 1 or Fig. 3, each of the analysers 28, 30 operates by periodically sampling the signal received from the sensor wire 12. Each sample is allocated a timestamp derived from a synchronising clock 36, so that the time relationship between the samples produced by each of the analysers 28, 30 is known.

Details of analyser arrangements and methods Fig. 3 can be used to describe the analyser arrangements and methods in more detail. In Fig. 3, the processor 34 is separate from each of the analysers 28, 30 but could alternatively be incorporated with one of them. In particular, the processor 34 could be incorporated within the analyser 28, resulting in a scheme generally as illustrated in Fig. 1, with the analyser 30 communicating back to the analyser 28, which also incorporates the processor 34. In either example, the correlation process can be completed by an arrangement such as that illustrated as the processor 34 of Fig. 3. The processor 34 is also illustrated in more detail in Fig. 4.

The processor 34 may be a general purpose computing device operating under appropriate software control to provide the functions which will be described, or may be a dedicated computing device, such as an ASIC (application specific integrated circuit). The processor 34 provides a storage buffer 38 for receiving samples from the first analyser 28, representing measurement samples of the signal 14 as received by the analyser 28. The storage buffer 38 may be a shift register or general purpose memory. A second buffer 40 similarly receives samples from the second analyser 30, representing measurement samples of the signal 14 as received by the analyser 30. Appropriate arrangements, such as a clock 36, allow the time relationship between samples in the shift registers 38, 40 to be determined.

The processor 34 also provides a combining circuit 42 for combining the samples in the buffers 38, 40. In this example, the combining circuit 42 is configured to combine pairs of samples from the buffers 38, 40, in order to multiply the value of each pair of samples and then calculate the sum of these products. The "sum of products" may be calculated from the whole of each data set (the entire contents of the buffers 38, 40) or may use only part of the data set. In one example, a subset of contiguous data points is selected from one data set and a sum of products is calculated with the corresponding subset of the other data set. In effect, this looks at each data set through a window which is smaller than the data set. Each "sum of products" calculation forms a single data point in a data set which is completed by creating further "sum of products" values. Further values can be created either after rotationally shifting the contents of one of the buffers (illustrated as the connection 44 for the buffer 40 in Fig. 3) or after moving the window used to select the subset of samples. The magnitude of the shift between each sum of products calculation may be a single position, or a larger number of positions. Each sum of products calculation yields a further data point for the data set which is collected by a data circuit 46.

Each shift changes the time correspondence between the samples in the buffers 38, 40. The result of a sum of products calculation will therefore change as the samples are shifted, and will reach a maximum when the shift corresponds to the time difference introduced between the signals received at each end 1 5, by any difference in the path length from the position 16 to the respective end 15.

Fig. 5 illustrates a data set created by a series of sum of products calculations by the combining circuit 42. The data set is shown with a horizontal axis representing the shift distance introduced in the register 40, and a vertical axis representing the sum of products value calculated by the combining circuit 42. In this example, the data set reaches a peak, generally at 48, when the change in the time relationship introduced by shifting the contents of the register 40 is equal to (or closest to) the difference in transit time arising from the difference in the path length to the respective ends 15. That is, the data set identifies the time separation of corresponding features of the signal 14 as received at each of the ends 15, since the maximum correlation will occur when the change in the time relationship has compensated for the difference in transit time, and restored the signals 14 to be in synchronisation.

Thus, the position of the peak 48 provides a value for the optimum shift distance in the buffer 40. The difference in the propagation time of the two signals received at the ends 15 is then given by dividing the optimum shift distance (expressed as the number of shifts within the register 40) by the sample rate used in the analysers 28, 30.

Having calculated the difference in the propagation time, the position of the original disturbance 16 can be calculated in various ways. In one example, the difference in the propagation time can be used to calculate a position based on an assumption that the propagation speed of the signal 14 is constant (or known) throughout the system. In an alternative, the calculated difference can be compared with calibration values previously created by disturbing the sensor wire 12 at known positions, from which it can be assumed that the current disturbance is located close to the known position which provides a calibration value closest to the currently calculated value.

The output 50 of the data circuit 46 represents either the position of the peak, the difference in the propagation time or the position of the disturbance, depending on whether further processing is to follow, or not.

The quality of the data analysis on which the data set of Fig. 5 is based depends on the number of register shifts between each calculation of a data point. In principle, the best data set is obtained by executing a shift of a single position between each calculation. However, this creates the maximum data processing workload for the combining circuit 42 and the data circuit 46. A smaller data set can be obtained by executing a shift of a greater number of positions between each calculation and employing an efficient algorithm to find the maximum. This reduces the data processing workload for the combining circuit 42 and the data circuit 46.

Alternatively, the data analysis may be used to determine that the result lies in a range of values rather than at a specific value. This corresponds with identifying the disturbance 16 in a zone of positions, rather than at a specific position. This may be sufficient in practical applications.

Further alternatives Many alternatives to the arrangements described above can be envisaged, without departing from the scope of the present invention.

For example, although the description has related to measurement of the magnitude of a signal received at the end of the sensor wire 12, there may be other signal attributes which change as a signal propagates, such as phase.

Other signal attributes can therefore be measured and used in the process of finding the position from the maximal correlation. That is, by finding the maximal correlation of the signals with respect to at least one other parameter of the signal (the "determinant" parameter), the position of the disturbance can be calculated either from the position of maximal correlation from the determinant or by the comparison of some parameter of the signal when the two signals are aligned with respect to the determinant parameter. The determinant parameter may be time, phase, or the time of a trigger based on the amplitude of the signal,

for example.

Many alternative technologies for signal detection, signal processing, data processing and analysis could be used, as will be readily apparent to the skilled reader.

Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.

Claims

CLAIMS1. Apparatus comprising: a signal conduit having two ends and operable to create a signal when disturbed between the ends, the signal thereafter propagating from the position of the disturbance to each of the ends; analyser means operable to detect the signal as received at each of the ends; and the analyser means being operable to find the maximal correlation of the signal as received at each of the ends, and to determine the position of the disturbance from the maximal correlation.
2. Apparatus according to claim 1, wherein the apparatus further comprises a communication channel operable for communicating the signal received at least at one of the ends, to the analyser means.
3. Apparatus according to claim 2, wherein the communication channel is provided separately from the signal conduit.
4. Apparatus according to claim 2, wherein the communication channel is provided in the same structure as the signal conduit.
5. Apparatus according to any of claims 2 to 4, wherein the communication channel is optical, mechanical, electrical or electromagnetic.
6. Apparatus according to any preceding claim, wherein the analyser means comprises an analyser operable to receive the signals from the respective ends of the signal conduit for correlation of the changes.
7. Apparatus according to any preceding claim, wherein the analyser means comprises first and second analysers operable separately to provide initial analysis of the signal received at respective ends of the signal conduit, and the analyser means being operable to combine the results to complete the correlation.
8. Apparatus according to claim 7, wherein the results of the initial analysis by one of the analysers is forwarded to the other analyser for completion of the correlation.
9. Apparatus according to any preceding claim, wherein the analyser means is operable to detect at least one parameter of the signal as received at each of the ends, the parameter changing as the signal propagates along the signal conduit.
10. Apparatus according to any preceding claim, wherein the received signals are correlated to detect a difference in at least one parameter of the signal as received at each of the ends, caused by a difference of path lengths along the signal conduit, thereby to determine the position of the disturbance.
11. Apparatus according to any preceding claim, wherein the correlation identifies the time separation of corresponding features of the signal as received at each of the ends, to identify differences in propagation delay.
12. Apparatus according to any preceding claim, wherein each of the received signals is periodically sampled, and the samples combined to complete the correlation.
13. Apparatus according to claim 12, wherein each of the samples is allocated a timestamp.
14. Apparatus according to claim 12 or 13, wherein the samples representing each of the received signals are stored, and a correlation value obtained by combining samples of one of the received signals with corresponding samples of the other received signal, and further correlation values are created by changing the correspondence between the samples, to yield a correlation curve.
15. Apparatus according to claim 14, wherein multiple correlation values are created, each representing a different time correspondence between the samples.
16. Apparatus according to claim 15, wherein each correlation value is calculated as a sum of products of the corresponding samples.
17. Apparatus according to claim 15 or 16, wherein each correlation value is obtained from all of the samples of the received signals, or subsets of the samples.
18. Apparatus according to claim 17, wherein the subsets contain contiguous samples.
19. Apparatus according to claim 17 or 18, wherein the analyser is operable to change the subset of samples used to obtain a correlation value.
20. Apparatus according to any of claims 12 to 19, wherein the apparatus further comprises buffers operable to store the samples.
21. Apparatus according to claim 20, wherein the analyser is operable to shift the contents of one buffer relative to those of the other buffer, and to obtain a correlation value at a plurality of shift positions.
22. Apparatus according to any preceding claim, wherein the signal conduit includes an electrical conductor movable, when disturbed, in a magnetic field, to create an electrical signal propagating along the conductor.
23. Amethodinwhich: a signal conduit having two ends is used to create a signal when disturbed between the ends, the signal thereafter propagating from the position of the disturbance to each of the ends; the signal is detected as received at each of the ends; and the signal is analysed to find the maximal correlation of the signal as received at each of the ends, and to determine the position of the disturbance from the maximal correlation.
24. A method according to claim 23, wherein the signal received at least at one of the ends is communicated to the other end for analysis.
25. A method according to claim 23 or 24, wherein a communication channel is provided separately from the signal conduit.
26. A method according to claim 23 or 24, wherein a communication channel is provided in the same structure as the signal conduit.
27. A method according to claim 25 or 26, wherein the communication channel is optical, mechanical, electrical or electromagnetic.
28. A method according to any of claims 23 to 27, wherein there is initial analysis of the signal received at respective ends of the signal conduit, followed by combining the results to complete the correlation.
29. A method according to any of claims 23 to 28, wherein at least one parameter of the signal as received at each of the ends is detected, the parameter changing as the signal propagates along the signal conduit.
30. A method according to any of claims 23 to 29, wherein the received signals are correlated to detect a difference in at least one parameter of the signal as received at each of the ends, caused by a difference of path lengths along the signal conduit, thereby to determine the position of the disturbance.
31. A method according to any of claims 23 to 30, wherein the correlation identifies the time separation of corresponding features of the signal as received at each of the ends, to identify differences in propagation delay.
32. A method according to any of claims 23 to 31, wherein each of the received signals are periodically sampled, and the samples combined to complete the correlation.
33. A method according to claim 32, wherein each of the samples is allocated a timestamp.
34. A method according to claim 32 or 33, wherein the samples representing each of the received signals are stored, and a correlation value obtained by combining each sample of one of the received signals with a corresponding sample of the other received signal, and further correlation values are created by changing the correspondence between the samples, to yield a correlation curve.
35. A method according to claim 34, wherein multiple correlation values are created, each representing a different time correspondence between the samples.
36. A method according to claim 35, wherein each correlation value is calculated as a sum of products of the corresponding samples.
37. A method according to any of claims 35 or 36, wherein each correlation is calculated from all of the samples of the received signals, or from subsets of the samples.
38. A method according to claim 37, wherein the subsets contain contiguous samples.
39. A method according to claim 37 or 38, wherein each correlation value is obtained from a different subset of samples.
40. A method according to any of claims 32 to 39, wherein the samples are stored in buffers.
41. A method according to claim 40, wherein the contents of one buffer are shifted relative to those of the other buffer, for obtaining a further correlation value, and a correlation value being obtained at a plurality of shift positions.
42. A method according to any of claims 23 to 41, wherein the signal conduit includes an electrical conductor movable, when disturbed, in a magnetic field, to create an electrical signal propagating along the conductor.
43. Apparatus substantiaHy as described above, with reference to the accompanying drawings.
44 A method substantially as described above, with reference to the accompanying drawings.
45. Any novel subject matter or combination including novel subject matter disclosed herein, whether or not within the scope of or relating to the same invention as any of the preceding claims.