WO2011073624A1

WO2011073624A1 - Improvements in or relating to sensing apparatus

Info

Publication number: WO2011073624A1
Application number: PCT/GB2010/002288
Authority: WO
Inventors: Adam Leonard Bridgen; John Barratt
Original assignee: Geoquip Limited
Priority date: 2009-12-17
Filing date: 2010-12-17
Publication date: 2011-06-23
Also published as: EP2513880A1; GB0922044D0

Abstract

A sensing apparatus (10) is provided which has an elongate magnetic core (20, 22) and a single electrical sensor conductor (12) which extends along a space (24) and is free to move relative to the core (20, 22). The space (24) extends longitudinally along the core (20, 22). The core (20, 22) provides magnetic flux within the space (24). Further the core (20, 22) provides a substantially continuous flux path, except at the space (24).

Description

Improvements in or Relating to Sensing Apparatus

The present invention relates to sensing apparatus.

In one aspect, the invention provides apparatus comprising: an elongate magnetic core; a single electrical sensor conductor extending along a space and free to move relative to the core, the space extending longitudinally along the core; and wherein the core provides magnetic flux within the space; and wherein the core provides a substantially continuous flux path, except at the space.

There may be a single space extending longitudinally along the core. The core may comprise a plurality of core pieces. The core may comprise core pieces which abut, the core pieces having a key and complementary keyway to maintain the relative alignment of the core pieces. The key and keyway may extend longitudinally along the core.

The space may be defined, at least in part, between a pair of core pieces. The pair of core pieces may grip a hollow member within which the conductor is contained and free to move. The hollow member may be tubular.

The apparatus may further comprise a sheath around the magnetic core, to hold the core pieces in their relative positions. The apparatus may further comprise a return conductor which is held substantially against movement relative to the core. The return conductor may be held between core pieces. Examples of the present invention, and their uses, 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 simple schematic diagram of an example apparatus;

Fig. 2 is a section at 2-2 of Fig. 1 , looking along the axis of the cable; and

Fig. 3 is an enlarged part of Fig. 2. Fig. 1 illustrates in very simple form the general arrangement of one example of a sensing apparatus in the form of an elongate cable 10. In most envisaged applications, the cable 10 will be much longer than illustrated in Fig. 1.

A single electrical sensor conductor 12 extends along the length of the cable 10 and is connected at 14 to a return conductor 16 which extends longitudinally back along the cable 10. Accordingly, the sensor conductor 12 and the return conductor 16 can both be connected to electrical apparatus 18 to complete an electrical circuit along the cable 10, having a first leg provided by the conductor 12, and a second leg provided by the return conductor 16.

The construction of the cable 10 is shown in more detail in the cross-section of Fig. 2. Part of Fig. 2, circled at 19, is shown further enlarged in Fig. 3. Briefly, the cable 10 comprises an elongate magnetic core 20, 22, which provides a space 24 extending longitudinally along the core 20, 22. The sensor conductor 12 extends along the space 24 and is free to move relative to the core 20, 22, particularly in the event of vibration or other mechanical disturbance of the cable 10. In this example, the sensor conductor is a multi-strand conductor. A single strand conductor could be used.

The core 20, 22 is made of magnetic material to provide magnetic flux within the space 24. Examples include extruded synthetic rubber bonded barium-ferrite powders or other extruded plastic materials containing ferrites. Outside the space 24, the core 20, 22 provides a substantially continuous flux path, except at the space, as will be described. In more detail, the core 20, 22 is made of a plurality of core pieces. In this example, there are two core pieces which are generally semi-circular in section to provide a generally circular cable 10. The core pieces 20, 22 meet approximately at a diameter of the cable 10. In Fig. 2, the boundary diameter is shown as generally horizontal and accordingly, the core pieces 20, 22 will hereafter be referred to as the upper core piece 20 and the lower core piece 22, but it is to be understood that this language is used solely for clarity of description, and no particular orientation is necessary for the core pieces, during use. The core pieces 20, 22 have abutting faces at 26, which include a key 28 and a complementary keyway 30 formed respectively in the lower core piece 22 and the upper core piece 20. The key 28 and keyway 30 extend longitudinally along the core in order to maintain the relative alignment of the core pieces 20, 22. In one example, the key 28 and keyway 30 extend longitudinally along the whole length of the core, which in turn extends along the whole length of the cable 10. In other examples, the core 20, 22 may be provided in several lengths, and the key 28 and keyway 30 may be provided continuously or intermittently.

Thus, in the example being described, the space 24 is provided between a pair of core pieces, namely the core pieces 20, 22. The magnetic material from which the core pieces 20, 22 are made gives rise to magnetic flux across the space 24. In one example, the magnetisation of the material of the core pieces 20, 22 may be arranged to provide magnetic pole configurations as indicated in Fig. 2 by the letters "N" and "S". Thus, the core pieces 20, 22 provide a substantially continuous flux path indicated generally at 32, through the body of the core pieces 20, 22, except at the space 24. In cross-section, as illustrated in Fig. 2, the core pieces 20, 22 provide a generally C-shaped magnet whose flux is concentrated in the space 24.

The pole configurations indicated in Fig. 2 will cause the core pieces 20, 22 to be magnetically attracted, thus tending to retain them together, as illustrated. They may be further retained by an outer sleeve 34, such as a polyurethane or other material, which may provide protection against the external environment, such as being waterproof and/or resistant to ultraviolet or other environmental degradation.

In addition to defining the space 24, the core pieces 20, 22 form jaws which grip a hollow member 36 in the form of a tube which extends longitudinally along the cable 10 and contains the sensor conductor 12. The tube 36 may be of nylon or other electrically insulating material. The tube 36 is oversize compared with the dimensions of the sensor conductor 12, as can clearly be seen in Fig. 2, so that the sensor conductor 12 is free to move transversely within the tube 36, in the event of any vibration or other mechanical disturbance of the cable 10.

The return conductor 16 is in the form of a conventional insulated multi-strand conductor and is located at the centre of the cable 10. The conductor 16 is also gripped between the core pieces 20, 22, so that the conductor 16 is held substantially against movement relative to the core pieces 20, 22.

In another example, there may be no return conductor within the cable 10 but instead, a separate return conductor may be provided, externally of the cable 10. The core pieces 20, 22 are surrounded by the outer sleeve 34, as noted above. Two further layers are provided in the structure, between the sleeve 34 and the core pieces 20, 22, as can be seen in Fig. 3, which is an enlarged partial section at the outer periphery of the cable 10. The outer surface of the core pieces 20, 22 is shown as wrapped in an electrical insulation layer 38, which may be a mylar insulation tape, for example. The insulation layer 38 is in turn wrapped in a layer 40 of non-magnetic screening material. The layer 40 is electrically coupled with an earthing wire 42 which runs longitudinally along the cable 10. Many other arrangements could be made for providing the cable 10 with adequate environmental protection, and with electrical and magnetic screening, particularly in the interests of adequate electromagnetic compatibility (EMC) compliance.

In the structure which has been described, all of the components except the single sensor conductor 12 are held in fixed relative positions, but the sensor conductor 12 is free to move laterally within the tube 36. The tube 36, and thus the sensor conductor 12, is in the space 24 and is thus exposed to the magnetic flux created in the space 24 by the core pieces 20, 22. In the event of any mechanical disturbance to the cable 10, sufficient to cause lateral movement of the sensor conductor 12 within the tube 36, a voltage will be generated in the sensor conductor 12, as a result of it moving within the magnetic field. This voltage will propagate along the sensor conductor 12 and/or the return conductor 16, allowing the generated voltage to be detected at the electrical apparatus 18, which may include an oscilloscope, for example. The size and frequency of the voltage generated in the sensor conductor 12 will be dependent upon the strength of the magnetic flux in the space 24 and upon how violently the sensor conductor 12 is disturbed.

The cable 10 can therefore be used in a wide range of applications to detect mechanical disturbance. For example, the cable 10 can be run out along a boundary, such as a fence, gate, wall or other suitable structure, to detect mechanical disturbance to the boundary, indicative of an intruder or other interference.

Many other shapes and geometries for the components described above can be envisaged without departing from the scope of the invention being described. Many alternative materials, dimensions and relative dimensions could be chosen. The use of a single sensor conductor is expected to provide advantages of signal fidelity. Other spaces could be left within the core 20, 22 and will affect the detailed geometry of the flux paths, but advantages arising from a single sensor conductor would remain.

Additional apparatus could optionally be incorporated, for example at 14a (Fig. 1) without significantly affecting the signal coupling of the sensor conductor 12 and the return conductor 16. The apparatus 14a may, for example, provide a mechanism to detect the integrity of the conductors 12, 16 or may fulfill some other function.

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

1. Apparatus comprising: an elongate magnetic core;

a single electrical sensor conductor extending along a space and free to move relative to the core, the space extending longitudinally along the core;

and wherein the core provides magnetic flux within the space;

and wherein the core provides a substantially continuous flux path, except at the space.

2. Apparatus according to claim 1 , wherein there is a single space extending longitudinally along the core.

3. Apparatus according to any preceding claim, wherein the core comprises a plurality of core pieces.

4. Apparatus according to any preceding claim, wherein the core comprises core pieces which abut.

5. Apparatus according to claims 3 or 4, wherein the core pieces have a key and complementary keyway to maintain the relative alignment of the core pieces.

6. Apparatus according to claim 5, wherein the key and keyway extend longitudinally along the core.

7. Apparatus according to any preceding claim, wherein the space is defined, at least in part, between a pair of core pieces.

8. Apparatus according to claim 7, wherein the pair of core pieces grip a hollow member within which the conductor is contained and free to move.

9. Apparatus according to claim 8, wherein the hollow member is tubular.

10. Apparatus according to any of claims 3 to 9, wherein the apparatus further comprises a sheath around the magnetic core, to hold the core pieces in their relative positions.

11. Apparatus according to any preceding claim, wherein the apparatus further comprises a return conductor which is held substantially against movement relative to the core.

12. Apparatus according to claim 11 , wherein the return conductor is held between core pieces.

13. Apparatus substantially as described above, with reference to the accompanying drawings.

14. 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.