WO2006/120435. A number of improvements are proposed over this prior art specification.

Summary of the Invention

In a first broad independent aspect, the invention provides a structural separation monitoring system or a structural separation monitor for monitoring a region of an existing separation such as a crack or joint of a structure located between a first side and a second side of said structure; said first and second sides displacing over time relative to one another; said system compris ing a first part and a second part; said parts being moveable relative to one another dependent upon the extent of structural separation; said first part being configured for attachment to the surface of said structure on said second side; at least one of said parts incorporating a magnet and at least the other incorporating one or more sensors for sensing the magnetic field of said magnet; and means for obtaining an output for one or more sensors. This configuration is particularly

advantageous for the sensing of the position of the first side relative to the second side of a structure. It lends itself to simple calculations to determine the positions particularly in the context of crack and/or joint monitoring.

In a subsidiary aspect, said magnet is a cylindrical magnet oriented normal to the surface to which it is mounted with a first pole at its upper extremity and a second pole at its lower extremity. This configuration of magnet lends itself advantageously to triangulation and therefore to improvements in the processing required to determine the relative position of the first and second part

In a further subsidiary aspect, the invention provides a sensor spaced apart from said magnet in the Z direction. This allows the determination of variations in the Z direction to be determined. Advantageously, there are at least three sensors to determine the variations in the X, Y and Z directions.

In a further subsidiary aspect, said one or more sensors are Hall Effect sensors. This configuration Is particularly advantageous for accurate and improved calculations of the relative positions of the first and second parts.

In a further subsidiary aspect, said sensors are spaced apart by a predetermined distance and located in a common X and Y plane. This configuration is particularly advantageous when implemented across the substantially planar structure.

In a further subsidiary aspect, said first part incorporates a cylindrical housing and said second part incorporates a further housing; said cylindrical housing and said further housing being distinct housings which are spaced from one another. This configuration is particularly advantageous to accommodate the cylindrical magnet but also lends itself to improved placement on a wall for example.

In a further subsidiary aspect, said first part incorporates a housing with a base portion incorporating adhesive for attaching said first part to said first side. In a further subsidiary aspect, said second part incorporates a housing with a base portion Incorporating adhesive for attaching said second part to said second side. This configuration is particularly advantageous in terms of securing the parts onto the relatively fragile portion of a structure. The interaction of the parts with their respective sides will have little or no impact on the integrity of the structure.

In a further subsidiary aspect, the system further compris es a template with predetermined separate apertures for receiving at least part of said first and second parts; said apertures being configured to locate said first and second parts at a predetermined distance from one another. The template is also advantageous in the calibration process since it allows the initial position of the magnet relative to the sensors to be known which avoids errors in measurement which would otherwise be introduced due to the Inherent variations in the magnetic properties of the magnet of each individual crack monitor. In a further subsidiary aspect, the system further compris es a temperature sensor and means for compensating out temperature variations.

In a second broad independent aspect, the invention provides a method of installing a structural separation monitoring system compris ing the steps of:

• Placing a first part and a second part of a system according to the first broad

independent aspect in a template;

• Providing adhesive on said first and second parts; locating said first and second parts respectively on first and second sides of the structure; and

· Allowing said adhesive to attach said parts to said sides and removing said template. This method allows a particularly precise installation whilst avoiding inflicting any damage to the structure. It avoids for example the requirement of drilling, In a third independent aspect the invention provides a method of measuring the structural separation between two sides of a structure compris ing the steps of:

• providing a structural separation monitor Incorporating a first part and a second part; allowing said parts to displace relative to one another dependent upon the extent of structural separation;

attaching said first part to the surface of said structure on said first side;

attaching said second part to the surface of said structure on said second side; providing one of said parts with a magnet;

providing said other part with one or more sensors for sensing the magnetic field of said magnet;

obtaining an output from one or more sensors; and

deriving a value of the separation between said parts dependent upon the obtained output from said sensors.

In a subsidiary aspect, the method comprises the step of deriving a value of the separation by triangulation taking into account the known distance between two sensors of said second part

In a fourth broad independent aspect, the invention provides a positional sensor comprising a first part and a second part; said parts being moveable relative to one another; said first part being configured to attach said first part to the surface of the structure; said second part being configured to attach said second part to the surface of the structure; at least one of said parts incorporating a magnet and at least the other incorporating one or more sensors for sensing the magnetic field of said magnet; and means for obtaining an output from one or more sensors; wherein said magnet is oriented normal to the surface to which it is mounted with a first pole at its upper extremity and a second pole at its lower extremity; said one or more sensors are Hall Effect sensors; and said sensors are spaced apart by a predetermined distance and are located in a common X and Y plane. The sensors may also advantageously be spaced apart by a predetermined angle.

Brief Description of the Figures

Figure 1 shows a schematic cross-sectional view of a monitoring system in accordance with a first embodiment of the invention. Figure 2 shows a plan view of the monitoring system of Figure 1.

Figure 3 shows a diagram of the relative positions of the sensors and the magnet Figure 4 shows an exploded perspective view of the first and second parts of the monitoring system and their corresponding installation template.

Figure 5 shows the installation template fitted with the first and second part where the annular surface of the first part and the disc-shaped surface of the second part are visible. These locations would be used for example to receive the adhesive.

Figure 6 shows the first and second part installed on a first and second side of a structure such as a wall incorporating a crack. Detailed Description

Basic Concept This embodiment consists of a magnet 1 and two or more magnetic field strength sensors 2 which are part of the monitoring device. The magnet is provided in a cylindrical housing 3 whilst the sensors are provided in a separate housing 4. The sensors 2 are arranged in such a way that the position of the magnet 1 can be calculated relative to the sensors 2. The sensors 2 are fixed relative to each other (their three dimensional relationship to each other being known) and the magnet is free to move. The magnet is fixed to one side 5 to the structural separation 6 and the monitoring device 7 containing the sensors 2 is fixed to the other side 8. The structural separation 6 is either a crack or a joint A value relative to the field strength is obtained from each sensor and then converted to a linear distance. Once the distance from each sensor to the magnet is known, the 3D position of the magnet relative to the sensors can be calculated. The embodiment typically consists of a magnet and only two sensors (see Figures 1-3), which enables the position of the magnet to be calculated in the X Y plane. However, with the addition of one or more sensors such as sensor 28, the position of the magnet can be calculated in the third dimension (Z). The sensor would be typically of the Hall Effect type. If a sensor is positioned in the field so that the lines 29 for flux are perpendicular to the sensor as in the illustration, then the magnetic field strength decreases with the inverse square of the distance from the magnet If when the sensor and the magnet move relative to each other they are kept in this condition, a simple calculation can be done to find the actual distance from the magnet to the sensor. The formula for doing so is

Once the distance respectively A and B from each sensor (2A, 2B) to the magnet 1 is known, the position of the magnet can be calculated relative to the sensors through triangulation. Distance C is fixed and known (see Figure 3). x = A*sin b y = A*cos b

The monitoring device contains the necessary electronics to obtain the output from the sensors and the means optionally to store, transit and/or process the data.

Method of Flying (see Figures 4-6)

For the systems to be accurate it is preferred that the magnet be in the right position and orientation to the monitoring device when initially installed. This is achieved by means of a temporary housing 9 that holds the magnet 10 and monitoring device 11 in exactly the right relationship to each other whilst the device is being fixed to the structure, it is envisaged that the device will be fixed by the means of a rapidly hardening adhesive rather than with screws. The magnet 10 and monitoring device 11 will be placed in the temporary housing, forming an assembly, and so that the back side is accessible. The adhesive will be of a high viscosity type. Adhesive will be applied to the back side of the magnet and monitoring device. The assembly will then be positioned correctly and pressure applied so the complete assembly sticks to the structure. Once the adhesive has hardened, the temporary housing 9 will be removed, leaving the magnet and monitoring device in the connect relationship to each other. The cylindrical magnet housing 10 houses the magnet which may be oriented in the Z direction with one of the poles at the upper potion and the other pole at a lower portion. The housing incorporates a flange 12 protruding radially outwards from the main cylindrical body of the housing 10. On the lower surface 13 of the housing, adhesive agent may be spread in order to readily secure housing 10 on a first side of a structure. The monitoring device 11 incorporates at extremity 14, an arcuous indent 15 which allows the appropriate alignment of the monitoring device with the cylindrical magnet housing. The fact that the cylindrical housing 10 and the monitoring device 11 are separate parts together with the arc-shaped adjacent surfaces allows, once the cylindrical housing is secured to a structure, the monitoring device to be positioned relative to the cylindrical housing in any radial direction. The monitoring device incorporates on its underside 16 a protruding cylindrical member 17. Member 17 may preferably incorporate a lip 18 extending about the drcumference of the cylindrical member. Lip 18 protrudes further than disc-shaped base face 19. The Up 18 and the base face 19 form together a receiving portion for receiving adhesive. The width of monitoring device 11 is not constant along its length. In particular, it incorporates a narrowing section such as narrowing section 20 on both sides of the device. These narrowing portions can be best seen in figure 5 as narrowing portions 20 and 21. On the upper portion of the monitoring device 11, as best seen In figure 6, an elongate cylindrical housing 22 is provided. It may for example house wireless transmission means which may allow the data gathered by the monitoring device to be transmitted to a remote receiver. A corresponding elongate cylindrical member 23 is provided in the recess 24 of template 9. Recess 24 corresponds precisely to the shape of the monitoring device so that the monitoring device may be retained in the recess whilst the process of adhering the monitoring device to a supporting structure such as a wall is completed. The template incorporates a further recess which is a cylindrically shaped recess 25 in which the body of the cylindrical housing 10 is located during the process of adhesion of the cylindrical housing to a side of the structural separation. This can best be seen in figure 6, when the cylindrical magnet housing 10 and the monitoring device 11 are secured to a supporting structure a gap 26 may be present between the two components. Furthermore, the extremity of the monitoring device which is closest to the cylindrical housing may overlap with the crack 27 without entering into contact with it The structure on which the monitoring device is secured is in this embodiment a brick walL