Piezocable based sensor for measuring unsteady pressures inside a pipe Number:7,367,239 from the United States Patent and Trademark Office (PTO) owispatent

Title: Piezocable based sensor for measuring unsteady pressures inside a pipe

Abstract: A piezocable-based sensor for measuring unsteady pressures inside a pipe comprises at least one cable extending around at least a portion of a circumference of the pipe. The cable includes a first electrical conductor, a piezoelectric material disposed around the first electrical conductor, and a second electrical conductor disposed around the piezoelectric material. The sensor provides a signal indicative of unsteady pressure within the pipe in response to displacement of the pipe. In various embodiments, a band is wrapped around the at least one cable for compressing the at least one cable toward the pipe. In other embodiments, the sensor includes a clamp attached to opposing ends of the at least one cable for holding the at least one cable in tension around the pipe.

Patent Number: 7,367,239 Issued on 05/06/2008 to Engel

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Inventors:	Engel; Thomas W. (East Hampton, CT)
Assignee:	CiDRA Corporation (Wallingford, CT)
Appl. No.:	11/089,089
Filed:	March 23, 2005

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Related U.S. Patent Documents

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	Application Number	Filing Date	Patent Number	Issue Date
	60564866	Apr., 2004
	60555589	Mar., 2004

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Current U.S. Class:	73/861.18
Current International Class:	G01F 1/20 (20060101)
Field of Search:	73/753,861.18

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Primary Examiner: Lefkowitz; Edward
Assistant Examiner: Patel; Punam

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Parent Case Text

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CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of U.S. Provisional Patent Application No. 60/555,589 filed Mar. 23, 2005, and U.S. Provisional Patent Application No. 60/564,866, filed Apr. 23, 2004; each of which is incorporated by reference herein in its entirety.

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Claims

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What is claimed is:

1. A sensor comprising: at least one cable extending around at least a portion of a circumference of a pipe, the at least one cable including: a first electrical conductor, a piezoelectric material disposed around the first electrical conductor, and a second electrical conductor disposed around the piezoelectric material; an electrical insulator disposed between the at least one cable and the pipe; and a clamp attached to opposing ends of the at least one cable for holding the at least one cable in tension around the pipe; wherein the at least one cable provides a signal indicative of unsteady pressure within the pipe.

2. The sensor of claim 1, wherein the at least one cable includes a plurality of cables having a common outer jacket for securing the plurality of cables together as a ribbon.

3. The sensor of claim 1, further comprising: a band wrapped around the at least one cable, wherein the band compresses the at least one cable toward the pipe.

4. The sensor of claim 3, wherein the at least one cable is attached to the band.

5. The sensor of claim 4, wherein the at least one cable is attached to the band by at least one of: adhesive, epoxy, and heat-shrink material.

6. The sensor of claim 3, further comprising: at least one spacer disposed between the band and the pipe, the at least one spacer being positioned proximate the ends of the at least one cable for preventing the ends of the at least one cable from being pinched when the band is tightened around the at least one cable.

7. The sensor of claim 1, further comprising: a protective sheet disposed between the at least one cable and the pipe.

8. The sensor of claim 1, wherein the at least one cable is mechanically coupled to a protective sheet, the protective sheet being disposed between the at least one cable and the pipe.

9. The sensor of claim 1, wherein the at least one cable includes a plurality of cables electrically connected in parallel.

10. The sensor of claim 1, wherein the first electrical conductor has a cross-sectional shape selected from one of: polygonal, substantially flat, oval, and ovoid.

11. The sensor of claim 1, wherein the first electrical conductor has a round cross-sectional shape.

12. A method of installing at least one sensor on a pipe, the method comprising: wrapping at least one cable around at least a portion of a circumference of the pipe, the at least one cable including: a first electrical conductor, a piezoelectric material disposed around the first electrical conductor, and a second electrical conductor disposed around the piezoelectric material; disposing an electrical insulator between the at least one cable and the pipe; attaching a clamp to opposing ends of the at least one cable for holding the at least one cable in tension around the pipe; and electrically connecting the at least one cable to provide an unsteady pressure within the pipe.

13. The method of claim 12, wherein the at least one cable includes a plurality of cables having a common outer jacket securing the plurality of cables together as a ribbon.

14. The method of claim 12, further comprising: tightening a band around the at least one cable, wherein the band compresses the at least one cable toward the pipe.

15. The method of claim 14, wherein the at least one cable is attached to the band before the at least one cable is wrapped around the pipe.

16. The method of claim 15, wherein the at least one cable is attached to the band by at least one of: adhesive, epoxy, and heat-shrink material.

17. The method of claim 14, further comprising: disposing at least one spacer between the band and the pipe, the at least one spacer being positioned proximate the ends of the at least one cable for preventing the ends of the at least one cable from being pinched when the band is tightened around the at least one cable.

18. An apparatus comprising: an array of sensors, having at least three sensors disposed at different axial locations along a pipe, wherein the sensor provides a signal indicative of unsteady pressure within the pipe, each of the sensors including at least one cable extending around at least a portion of a circumference of the pipe, each cable including: a first electrical conductor, a piezoelectric material disposed around the first electrical conductor, a clamp attached to opposing ends of the each cable for holding each cable in tension around the pipe; and a second electrical conductor disposed around the piezoelectric material; an electrical insulator disposed between the at least one cable and the pipe; and a signal processor configured to: receive the signal indicative of unsteady pressure within the pipe from the at least one cable in each sensor, and determine a parameter of the fluid in response to the signals.

19. The apparatus of claim 18, wherein the parameter of the fluid includes at least one of density of the fluid, volumetric flow rate of the fluid, mass flow rate of the fluid, composition of the fluid, entrained air in the fluid, consistency of the fluid, size of particles in the fluid, and health of a device causing the unsteady pressures to be generated in the pipe.

20. The apparatus of claim 18, wherein the signal processor determines a velocity of the fluid in the pipe and/or a speed of sound propagating though the fluid in response to an array processing algorithm.

21. The apparatus of claim 18, wherein the array of sensors are interconnected to maintain proper spacing therebetween.

22. The apparatus of claim 18, further comprising: a plurality of bands, one of the plurality of bands wrapped around a corresponding one of the plurality of cables and securing the corresponding cable to the pipe.

23. The apparatus of claim 22, further comprising: a plurality of spacers, at least one of the plurality of spacers disposed between each of the plurality of bands and the pipe, the spacers being positioned proximate the ends of the cables for preventing the ends of the cables from being pinched when the band is tightened around the cables.

24. The apparatus of claim 22, wherein each cable is attached to a respective band.

25. The apparatus of claim 24, wherein each cable is attached to a respective band by at least one of: adhesive, epoxy, and heat-shrink material.

26. The apparatus of claim 22, further comprising: at least one spacer disposed between the band and the pipe, the at least one spacer being positioned proximate the ends of each cable for preventing the ends of each cable from being pinched when the band is tightened around each respective cable.

27. The apparatus of claim 18, further comprising: a protective sheet disposed between each cable and the pipe.

28. The apparatus of claim 18, wherein each cable is mechanically coupled to a protective sheet, the protective sheet being disposed between each cable and the pipe.

29. The apparatus of claim 18, wherein each cable includes a plurality of cables electrically connected in parallel.

30. A sensor comprising; a plurality of cables disposed adjacent to each other in a common plane and extending around at least a portion of a circumference of a pipe, each of the cables including: a first electrical conductor, a piezoelectric material disposed around the first electrical conductor, and a second electrical conductor disposed around the piezoelectric material; at least one electrical insulator disposed between the plurality of cables and the pipe; and a clamp attached to opposing ends of the plurality of cables for holding the plurality of cables in tension around the pipe; wherein the plurality of cables provide a respective signal indicative of unsteady pressure within the pipe.

31. The sensor of claim 30, wherein the plurality of cables have a common outer jacket for securing the plurality of cables together as a ribbon.

32. The sensor of claim 30, wherein the plurality of cables are each discrete cables separate from each other.

33. The sensor of claim 30, wherein the plurality of cables have a common outer jacket over at least a portion of the length of the cables.

34. The sensor of claim 30, wherein the common plane of the plurality of cables is parallel to the outer surface of the pipe.

35. The sensor of claim 30, further comprising: a band wrapped around the plurality of cables, wherein the band compresses the plurality of cables toward the pipe.

36. The sensor of claim 35, wherein the plurality of cables is attached to the band.

37. The sensor of claim 36, wherein the plurality of cables is attached to the band by at least one of: adhesive, epoxy, and heat-shrink material.

38. The sensor of claim 35, further comprising: at least one spacer disposed between the band and the pipe, the at least one spacer being positioned proximate the ends of the plurality of cables for preventing the ends of the plurality of cables from being pinched when the band is tightened around the plurality of cables.

39. The sensor of claim 30, further comprising: a protective sheet disposed between the plurality of cables and the pipe.

40. The sensor of claim 30, wherein the plurality of cables is mechanically coupled to a protective sheet, the protective sheet being disposed between the plurality of cables and the pipe.

41. The sensor of claim 30, wherein the plurality of cables are electrically connected in parallel.

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Description

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BACKGROUND OF THE INVENTION

1. Technical Field

The present invention generally relates to an apparatus for measuring unsteady pressures inside a pipe; and more particularly to an apparatus for measuring the same using a piezocable based sensor disposed on an outer surface of the pipe.

2. Background

A fluid flow process (flow process) includes any process that involves the flow of fluid through pipe, ducts, or other conduits, as well as through fluid control devices such as pumps, valves, orifices, heat exchangers, and the like. Flow processes are found in many different industries such as the oil and gas industry, refining, food and beverage industry, chemical and petrochemical industry, pulp and paper industry, power generation, pharmaceutical industry, and water and wastewater treatment industry. The fluid within the flow process may be a single phase fluid (e.g., gas, liquid or liquid/liquid mixture) and/or a multi-phase mixture (e.g. paper and pulp slurries or other solid/liquid mixtures). The multi-phase mixture may be a two-phase liquid/gas mixture, a solid/gas mixture or a solid/liquid mixture, gas entrained liquid or a three-phase mixture.

Various sensing technologies exist for measuring various physical parameters of single and/or multiphase fluids in an industrial flow process. Such physical parameters include, for example, volumetric flow rate, composition, consistency, density, and mass flow rate. Problematically, many sensors must be placed in contact with the fluid and, as a result, cannot be installed, moved or otherwise reconfigured without shutting down a portion of the flow process to install the sensors.

Various non-intrusive sensors have been developed, which are attached to the surface of the pipe. Such sensors include, for example, the ultrasonic transmitter and receiver found in ultrasonic flow meters. While ultrasonic flow meters perform well for certain applications, they are generally limited to use with certain fluid types and/or temperatures. Moreover, precise alignment of the ultrasonic transmitter and receiver pair is required, which may not lend itself to instrument portability and adaptability to different pipe sizes.

In some cases, sensors subjected to severe environmental conditions, such as high temperatures, water spray, precipitation, unintended contact, and the like. Where sensors are used in such conditions, they must be robustly designed to withstand these conditions while maintaining accuracy.

Thus, there remains a need for a robust, non-invasive sensor for measuring various parameters of single and/or multiphase fluids in an industrial flow process that is easily installed and which may be adaptable to different pipe sizes.

SUMMARY OF THE INVENTION

The above-described and other needs are met by a sensor comprising at least one cable extending around at least a portion of a circumference of the pipe. The at least one cable includes: a first electrical conductor, a piezoelectric material disposed around the first electrical conductor, and a second electrical conductor disposed around the piezoelectric material. The at least one cable provides a signal indicative of unsteady pressure within the pipe in response to displacement of the pipe. The at least one cable may include a plurality of cables connected in parallel, and the plurality of cables may have a common outer jacket for securing the plurality of cables together as a ribbon.

In various embodiments, a band is wrapped around the at least one cable and compresses the at least one cable toward the pipe. The at least one cable may be attached to the band. For example, the at least one cable may be attached to the band by at least one of: adhesive, epoxy, and heat-shrink material. At least one spacer may be disposed between the band and the pipe, with the at least one spacer being positioned proximate the ends of the at least one cable for preventing the ends of the at least one cable from being pinched when the band is tightened around the at least one cable. A protective sheet and/or an electrical insulator may be disposed between the at least one cable and the pipe.

In various embodiments, the at least one cable may be mechanically coupled to a protective sheet, with the protective sheet being disposed between the at least one cable and the pipe. In other embodiments, a clamp is attached to opposing ends of the at least one cable for holding the at least one cable in tension around the pipe.

In another aspect, a method of installing at least one sensor on a pipe comprises: wrapping at least one cable around at least a portion of a circumference of the pipe; and electrically connecting the at least one cable to provide a signal indicative of unsteady pressure within the pipe in response to displacement of the pipe. The at least one cable includes: a first electrical conductor, a piezoelectric material disposed around the first electrical conductor, and a second electrical conductor disposed around the piezoelectric material. The at least one cable may further include a plurality of cables having a common outer jacket securing the plurality of cables together as a ribbon.

In various embodiments, the method further includes tightening a band around the at least one cable, wherein the band compresses the at least one cable toward the pipe. The at least one cable may be attached to the band before the at least one cable is wrapped around the pipe. For example, the at least one cable may be attached to the band by at least one of: adhesive, epoxy, and heat-shrink material. The method may further include disposing at least one spacer between the band and the pipe, with the at least one spacer being positioned proximate the ends of the at least one cable for preventing the ends of the at least one cable from being pinched when the band is tightened around the at least one cable.

In another aspect, an apparatus comprises a spatial array of sensors disposed at different axial locations along a pipe. Each of the sensors includes at least one cable extending around at least a portion of a circumference of the pipe, and each cable includes: a first electrical conductor, a piezoelectric material disposed around the first electrical conductor, and a second electrical conductor disposed around the piezoelectric material. A signal processor is configured to receive a signal indicative of unsteady pressure within the pipe from the at least one cable in each sensor and determine a parameter of the fluid using the signals. The parameter of the fluid may include at least one of: density of the fluid, volumetric flow rate of the fluid, mass flow rate of the fluid, composition of the fluid, entrained air in the fluid, consistency of the fluid, size of particles in the fluid, and health of a device causing the unsteady pressures to be generated in the pipe.

The foregoing and other objects, features and advantages of the present invention will become more apparent in light of the following detailed description of exemplary embodiments thereof.

BRIEF DESCRIPTION OF THE DRAWING

Referring now to the drawing wherein like items are numbered alike in the various Figures:

FIG. 1 is a schematic depiction of a spatial array of piezocable based sensors for measuring unsteady pressures inside a pipe, in accordance with an embodiment of the present invention.

FIG. 2 is a cross-sectional view of a piezocable ribbon that may be used with the sensor of FIG. 1.

FIG. 3 is a partial, cross-sectional, side elevation view of one of the sensors 15 of FIG. 1.

FIG. 4 is a cross-sectional view of one of the sensors 15 taken along section 3-3 of FIG. 3.

FIG. 5 is a partial plan view of one of the sensors 15 of FIG. 1 disposed on the pipe 14.

FIG. 6 is a schematic depiction of the array of sensors of FIG. 1 in various stages of installation.

FIG. 7 is a side perspective view of a piezoelectric sensor sheet.

FIG. 8 is a schematic depiction of a spatial array of piezocable based sensors for measuring unsteady pressures inside a pipe, in accordance with another embodiment of the present invention.

FIG. 9 is an exploded plan view of a sensor in the array of FIG. 8.

FIG. 10 is an exploded elevation view of the sensor in the array of FIG. 8.

FIG. 11 is a schematic depiction of the array of FIG. 8 in one stage of installation onto a pipe.

FIG. 12 is a schematic depiction of the array of FIG. 8 installed on a pipe.

FIG. 13 is a schematic depiction of a spatial array of piezocable based sensors for measuring unsteady pressures inside a pipe, in accordance with another embodiment of the present invention.

FIG. 14 is a schematic depiction of an apparatus including the spatial array of piezocable based sensors for measuring at least one parameter of a fluid, in accordance with various embodiments of the present invention.

FIG. 15 is a block diagram of a diagnostic logic used in the apparatus of the present invention.

FIG. 16 is a block diagram of a first embodiment of a flow logic used in the apparatus of the present invention.

FIG. 17 is a cross-sectional view of a pipe having coherent structures therein.

FIG. 18 a k.omega. plot of data processed from an apparatus embodying the present invention that illustrates slope of the convective ridge, and a plot of the optimization function of the convective ridge.

FIG. 19 is a block diagram of a second embodiment of a flow logic used in the apparatus of the present invention.

FIG. 20 a k.omega. plot of data processed from an apparatus embodying the present invention that illustrates slope of the acoustic ridges.

FIG. 21 is a plot of mixture sound speed as a function of gas volume fraction for a 5% consistency slurry over a range of process pressures.

FIG. 22 is a plot of sound speed as a function of frequency for air/particle mixtures with fixed particle size and varying air-to-particle mass ratio.

FIG. 23 is a plot of sound speed as a function of frequency for air/particle mixtures with varying particle size where the air-to-particle mass ratio is fixed.

DETAILED DESCRIPTION

Referring to FIG. 1, a schematic depiction of an array 11 of piezocable based sensors 15 disposed at different axial locations x.sub.1 . . . x.sub.N along a pipe 14 for measuring unsteady pressures inside the pipe 14 is shown. Each sensor 15 comprises a plurality of cables 2 extending around at least a portion of the circumference of the pipe 14. Each cable 2 includes: an inner (first) electrical conductor 4, a piezoelectric material 5 disposed around the inner electrical conductor 4, and an outer (second) electrical conductor 6 disposed around the piezoelectric material 5.

The cable 2 provides a signal indicative of unsteady pressure within the pipe 14 in response to displacement of the pipe 14. More specifically, displacement of the pipe 14, as may be caused by one or both of acoustic waves propagating through a fluid 13 within the pipe and/or pressure disturbances that convect with the fluid 13 flowing in the pipe 14 (e.g., turbulent eddies and vortical disturbances), cause the cable 2 to be strained longitudinally and/or strained radially. In response to this longitudinal and/or radial strain, the piezoelectric material 5 generates a varying electrical charge between the inner and outer conductors 4, 6. The electrical charge varies in proportion to the amount of longitudinal and/or radial strain, and thus provides indication of the amount of displacement of the pipe 14 and, therefore, provides indication of the acoustic waves propagating through the fluid 13 within the pipe 14 and/or pressure disturbances that convect with the fluid 13 flowing in the pipe 14. The varying electrical charge, which may be amplified, impedance converted, and otherwise conditioned (e.g., filtered), is provided as the output signal P(t) from each sensor 15. As will be discussed in further detail hereinafter, these signals P.sub.1(t) . . . P.sub.N(t) may be used to determine one or more parameters of the fluid 13, such as: density of the fluid 13, volumetric flow rate of the fluid 13, mass flow rate of the fluid 13, composition of the fluid 13, entrained air in the fluid 13, consistency of the fluid 13, size of particles in the fluid 13, and health of a device causing the unsteady pressures to be generated in the pipe 14.

In the embodiment of FIG. 1, a band 3 (shown in phantom) is disposed around the plurality of cables 2 for compressing the plurality of cables 2 toward the pipe 14. Each of the sensors 15 includes at least one length of piezoelectric cable 2 secured along a portion of the length of the band 3. In this embodiment, displacement of the pipe 14, as may be caused by one or both of acoustic waves propagating through a fluid 13 within the pipe and/or pressure disturbances that convect with the fluid 13 flowing in the pipe 14 (e.g., turbulent eddies and vortical disturbances), cause the cable 2 to be strained longitudinally and/or strained radially against the outer band 3.

The band 3 is formed from a relatively rigid material in comparison to the piezoelectric material 5. For example, the band 3 may be formed from metal, fiberglass, polymers, and the like. A lubricating material may be disposed between the band and the cables 2 to prevent binding between the band 3 and cables 2. The band 3 may also be spring loaded (e.g., a spring loaded hose clamp) to insure good contact with the cable 2 in the presence of long term settling.

In each cable 2, the inner conductor 4 forms a core of the cable 2 and is comprised of strands of electrically conductive material (e.g., copper, aluminum, and the like). It is also contemplated that the inner conductor 4 may be solid, or may be strands or an extrusion disposed around another rigid material that forms the core of the cable 2. The piezoelectric material 5 is helically wrapped around the inner conductor 4, although the scope of the invention is intended to include embodiments in which the piezoelectric material 5 is otherwise braided, extruded, or molded around the inner conductor 4. The piezoelectric material 5 may include any piezo-active material (e.g., polyvinylidene fluoride (PVDF)), and may include copolymers of PVDF and other materials such as trifluoroethylene (TrFE) or tetrafluorethylene (TFE). For example, a description of piezoelectric materials is provided in J. S. Harrison and Z. Ounaies, Piezoelectric Polymers, NASA/CR-2001-211422 ICASE Report No. 2001-43, ICASE Mail Stop 132C NASA Langley Research Center Hampton, Va. 23681-2199, December 2001, pp. 31. The cable 2 is shown as having a circular cross section. It is contemplated, however, that any convenient cross-sectional shape of the cable 2 and/or inner conductor 4 may be used, such as polygonal (e.g., triangular, quadrilateral (e.g., square, rectangular), pentagonal, hexagonal, heptagonal, octagonal, etc.), substantially flat, oval, or ovoid shapes.

The outer conductor 6 is shown as braided strands of electrically conductive material (e.g., copper, aluminum, and the like). It is also contemplated that the outer conductor 6 may be wrapped, extruded, or deposited around the piezoelectric material 5. One example of a cable 2 that may be used with the present invention is commercially available from Measurement Specialties, Inc. of Fairfield, N.J. as part number 1005801-1 or 1005646-1.

Within each sensor 15, the cables 2 may be arranged parallel to, and in contact with, an adjacent cable 2 in the sensor 15, such that the outer conductors 6 of each cable 2 in the array are in electrical connection. The inner conductors 4 may be electrically connected at one end (e.g., by a soldered connection). The cables 2 in each sensor 15 are effectively electrically connected in parallel. The inner and outer conductors 4, 6 of one cable 2 may be coupled by way of an industrial connector to a non-piezoelectric terminal cable 17, such as a low noise coaxial cable to avoid triboelectrically generated noise in the signal from terminal cable 17 shaking and the like. Each terminal cable 17 conducts a respective signal P.sub.1(t) . . . P.sub.N(t) indicative of unsteady pressure within the pipe 14 to electronic circuitry, as will be described in further detail hereinafter. The ends of the cables 2 opposite the terminal cable 17 are mechanically unrestrained to prevent an overly constrained system.

While the embodiment of FIG. 1 shows the cables 2 in each sensor 15 contacting each other in side-by-side fashion, it is contemplated that other arrangements may be used. For example, the cables 2 may be separated by a dielectric (electrically insulative) material. For example, as shown in FIG. 2, the plurality of cables may have a common outer jacket 7 securing the cables together as a ribbon. The jacket 7 may be formed from any electrically insulative (dielectric) material to environmentally seal the cable 2 and protect it against thermal stimulus. For example, the jacket 7 may be formed from polyethylene or the like.

FIG. 3 illustrates a partial, cross-sectional, side elevation view of one of the sensors 15 disposed on the pipe 14. FIG. 4 illustrates a cross-sectional view of one of the sensors 15 taken along section 3-3 of FIG. 3, and FIG. 5 illustrates a partial plan view of one of the sensors 15 disposed on the pipe 14.

As best seen in FIG. 4, the cables 2 are secured to the band 3 by any suitable means such as, for example, adhesive, epoxy, and/or heat-shrink material. In the embodiment of FIG. 4, the cables 2 are secured to the band 3 by a sheath 12 of heat-shrink material.

Referring to FIGS. 3 and 5, the ends of the band 3 are releasably attached together by a fastener 23 comprising a screw mechanism similar to that of a typical hose clamp. The present invention contemplates that any fastening means, such as bolts, screws, rivets, epoxy, and adhesive, may be used to connect the ends of the bands 3.

Each of the sensors 15 includes at least one spacer 25 disposed between the band 3 and the pipe 14. The spacers 25 are positioned proximate the ends of the plurality of cables 2 for preventing the ends of the cables 2 from being pinched when the band 3 is tightened around the cables 2. The spacers 25 also help to ensure the pressure applied by the band 3 is substantially similar along the length of the cable 2. In the embodiment shown, each of the spacers 25 have an outer contour or chamfer 27 that engages the band 3 proximate each end.

Referring to FIG. 6, the array 11 of sensors 15 is shown in various stages of installation. The installation process begins with cleaning a surface of the section of pipe 14 onto which the sensors 15 are to be installed. This may include removing any debris on the pipe 14 to provide a smooth surface for receiving the sensors 15. A sheet or coating of electrically insulative material 200 is then applied around the pipe 14. For example, a sheet of Kapton.RTM. polymide, commercially available from E. I. du Pont de Nemours and Company of Wilmington, Del., may be used.

Next, a protective sheet 202 is wrapped around the pipe 14, over the electrically insulative material 200, and secured in place. The protective sheet 202 may be secured in place using springs or clamps 203 extending between the ends of the protective sheet 202. The electrically insulative material 200 extends continuously beneath the protective sheet 202 and protrudes from the ends of the protective sheet 202 for providing electrical insulation between the protective sheet 202 and the pipe 14.

The protective sheet 202 may be formed from a rigid material (e.g., metals, plastics, polymers etc.) that can be wrapped around the pipe 14. As best seen in FIG. 6, the protective sheet 202 includes a plurality of spaced-apart tabs 204 protruding therefrom in a direction away from the pipe 14. The tabs 204 define sides of raceways 206, which extend circumferentially around the pipe 14 (substantially perpendicular to the pipe axis) for receiving the sensors 15. One raceway 206 is provided for each sensor 15 to be installed. The tabs 204 maintain the desired sensor 15 location and spacing during assembly and operation. In addition, the protective sheet 202 protects the sensors 15 from heat, moisture, and other adverse conditions that may be associated with the pipe 14.

Once the protective sheet 202 is in place, each sensor 15 is aligned with a raceway 206 (as indicated at 15'). The sensor 15 is then wrapped around the protective sheet 202, and the fastener 23 is tightened to secure the sensor 15 in place (as indicated at 15''). After all of the sensors 15 have been installed, the springs or clamps 203 may be removed. The terminal cables 17 from each of the sensors 15 may be mechanically secured to a convenient structure, and the cables 17 are electrically connected to a signal processor (described hereinafter) or to other associated electronics (e.g., a charge amplifier for impedance conversion of the output signals from the sensors 15), which are in turn coupled to the signal processor.

It is contemplated that the sensors 15 may be mounted, attached or clamped directly onto the outer surface of the pipe 14, without the use of the protective sheet 202 or electrically insulative material 200. Alte