Blast movement monitor

1. A blast movement monitor for measuring the movement of material within a body of material as a result of a blasting operation, the monitor including:

a housing having an interior chamber defining an inner surface; and

an internal communication device that is received immediately within the interior chamber of the housing, the internal communication device including:

a cylindrical body portion;

an end portion formed integrally with one end of the body portion in order that the end portion and body portion define a cavity that is closed at one end by the end portion

an electric coil wound around the body portion;

a circuit board electrically connected to the coil;

a battery electrically connected to the circuit board;

the battery and circuit board being housed within the cavity; and

a cap associated with an opposing end of the body portion that encapsulates the body portion and sealingly houses the body portion thereby insulating the body portion, electric coil, circuit board and the battery from the external environment;

wherein the internal communication device is biased to facilitate self-righting of the internal communication device to a desired orientation within the interior chamber independent of the orientation of the monitor.

2. A blast movement monitor according to claim 1 , wherein the electric coil is wound on an external surface of the body portion.

3. A blast movement monitor according to claim 1 , wherein the electric coil is moulded and wound within material forming the body portion.

4. A blast movement monitor according to claim 1 , wherein the end portion and cap of the internal communication device have clearances grater than 1 mm, preferably at least 3.5 mm, from the inner surface of the internal chamber.

5. A blast movement monitor according to claim 1 , wherein an electrical current can be passed through the electric coil to generate an electro-magnetic field.

6. A blast movement monitor according to claim 1 , wherein the battery and the printed circuit board are encased in an epoxy resin within the cavity of the body portion.

7. A blast movement monitor according to claim 1 , wherein the center of mass of the internal communication device is axial and below a center point of the internal communication device so that the internal communication device aligns itself vertically within the interior chamber independent of the orientation of the monitor.

8. A blast movement monitor according to claim 1 , wherein the end portion and cap have curved outer surfaces.

9. A blast movement monitor according to claim 8 , wherein the end portion and cap form a sphere when the cap is secured to the body portion.

10. A blast movement monitor according to claim 9 , wherein the inner surface of the housing is curved.

11. A blast movement monitor according to claim 1 , wherein the cap is adhered or welded to the body portion.

12. A blast movement monitor according to claim 1 , wherein the housing contains a liquid intermediate the internal communication device and the inner surface of the housing to assist freedom of movement of the internal communication device relative to the housing.

13. A blast movement monitor according to claim 1 , wherein the housing is formed from a plastics material and includes two halves releasably attached to each other to enable the housing to be opened to provide access to the internal communication device.

14. A blast movement monitor according to claim 1 , wherein the housing is formed from a plastics material and includes two halves adhered or welded to one another.

15. An apparatus for determining the movement of a boundary between different portions of a body of material as a result of a blast, the apparatus including:

at least one blast movement monitor as claimed in any one of the preceding claims; and

an external communication device for communicating with the internal communication device of the blast movement monitor.

16. An apparatus according to claim 15 , wherein the external communication device is a detector for detecting signals transmitted by the internal communication device.

17. An apparatus according to claim 16 , wherein the detector is a magnetic field detector and includes a magnetic coil tuned to a frequency corresponding to a frequency of the signals transmitted by the internal communication device.

18. An apparatus according to claim 16 , wherein the detector includes an amplifier operatively coupled to the detector.

19. An apparatus according to claim 16 , wherein the detector is hand held and portable.