The present invention relates broadly to switch mechanisms and methods for activating switch mechanisms and, in particular, discloses improvements upon the switch mechanism first disclosed in Australian Patent Application No. P07404 which formed the basis of International Patent Application No. PCT/AU90/00181 (WO 90/13879), the disclosure of which is hereby incorporated by cross-reference.

International Application No. PCT/AU90/00181 discloses a switch assembly which includes a magnetically operable switch that is activated by the relative relocation of a contact block and a rotatable boss to provide a connection between two contact pads. The switch assembly provides for dual operation whereby, for normal operation the boss is rotated relative to the contact block so as to actuate the magnetically operable switch. For emergency operation, the boss and contact block are adapted to be rotated together such that the relative movement of the contact pads provide for an interconnection between terminals connected thereto.

The switch assembly as described was developed as part of a location marker/emergency distress device such as a flashing strobe light or a radio transmitter. The construction was such that when sealed to a casing, generally by a threaded connection sealed with an 0-ring, the switch assembly provided for water tight and gas proof switching and was thus suitable for use in. all climates, weather conditions and in hazardous industries such as the petro-chemical industry. Furthermore, the switch is only "operable under definite movements of the hands of a user which thereby prevented inadvertent switching.

However, there are various applications in which weather resistant switching is required and under which it is preferred that no manual switching action take place. Summary of the Invention

It is an object of the present invention to substantially overcome, or ameliorate, these problems through provision of an alternate activation mechanism for the prior art switch. In accordance with one aspect of the present invention there is disclosed a switch assembly comprising a casing including a magnetically operable switch arranged to selectively connect and disconnect at least two contact terminals,

a magnet arranged in said casing adjacent said switch to permit activation and closure of said switch, and a trip plate positionable between said magnet and said switch to prevent activation and closure of said switch. Brief Description of the Drawings

A number of preferred embodiments of the present invention will now be described with reference to the drawings in which:

Fig. 1 shows one preferred embodiment used in a life raft configuration shown in an armed position; Fig. 2 is an exploded perspective of Fig. 1;

Fig. 3 is an exploded perspective view of the switch assembly of Fig. 1 and Fig. 2;

Fig. 4A is an inverse plan view of an alternate contact block; and

Fig. 4B is a side cross-section of a second embodiment incorporating the contact block of Fig. 4A.

Best and Other Modes for Carrying Out the Invention

Referring to Figs. 1 and 2, an electrical device 1 corresponding to that disclosed in International Application No. PCT/AU90//00181 is shown provided with a switch assembly 10 and a strobe lamp 3. The specific embodiment of Fig. 1 is intended for life raft operations and a float collar 2 is arranged about the device 1 so as to ensure positive buoyancy and to maintain the strobe lamp above water level when in emergency situations. The device 1 is ountable to a bulkhead (not illustrated ⁾ via a mounting bracket 4 which includes spring clips 5 which clasp around a casing of the device 1. The device 1 is provided with a ring 9 which allows for connection of a life raft lanyard 8 which interconnects to the device 1 with a life raft mountable adjacent to the bulkhead (not illustrated). In operation, should the life raft be released from its mounting on the ship or vessel, the device 1 is pulled from the mounting bracket 4 via the lanyard 8.

A trip plate 6 is interposed between a rotatable boss 11 and a contact block 12 of the switch assembly 10. The trip plate 6 is formed of magnetically shielding material whereby the switch assembly 10 can be "armed" in which the magnet (see Fig. 3) in the boss 11 is aligned with the magnetically operable switch (see Figs. 4A and 4B for example ⁾ within the contact block 12 which enables operation of the device 1 and the subsequent flashing of the strobe lamp 3. However, with the trip plate 6

interposed between the boss 11 and the contact block 12, the trip plate 6 prevents the operation of the magnetically operable switch. The trip plate 6 is connected to the mounting bracket 4 via a lanyard 7. The trip place 6 is held in position between the boss 11 and the contact block 12 by an interference fit such that, when the device ! is pulled from the bracket 4, the trip plate 6, which is retained by the lanyard 7, is pulled from its position interposed between the boss 11 and the contact block 12. Accordingly, once clear of the trip plate 6, the switch assembly 10 operates in its normal function whereby the alignment of the magnet and the magnetically operable switch allow energisation of the device 1 and the flashing of the strobe lamp 3.

Figs. 1 and 2 also show a bandolier attachment 25 in which the device 1 can be secured to the body of a user. In such a*, configuration, the lanyard 7 can, for example, be secured to the bulkhead in any fashion whereby the device 1 can act as a man-overboard marker should the user fall overboard. In such applications, the lanyard 8 is not required.

Fig. 3 is an illustration similar to Fig. 6A of International Application No. PCT/AU90/00181 and illustrates how, the trip plate 6 is interposed between the boss 11 and the contact block 12. The boss 11 is provided with posts 14 and 15 which are adapted to mate with corresponding recesses (not shown) formed in the contact block 12. The switch boss 11 is rotatably connected to the contact block 12 via a spigot 13 having a spring 19 and secured by a nut 26 thereby providing a resilient force which maintains interconnection between the boss 11 and the contact block 12. A magnet 18 is provided in the boss 11 to activate, upon rotation of the boss 11, a magnetically operable switch (not illustrated in Fig. 3) located in the contact block 12. The magnetically operable switch a Reed switch or a Hall effect device for example. The trip plate 6 acts to prevent magnetic flux from the magnet passing to the magnetically operable switch that can caused activation. Preferably, the trip plate is manufactured of ferromagnetic materials of which stainless steel is a good example. As seen in Fig. 3, the trip plate 6 includes a series of notches 21, 22 and 23 which are respectively shaped so as to substantially mate with the spigot 13, and the posts 15 and 14 respectively. In this manner, the trip plate 6 can be inserted between the boss 11 and the contact block 12 and the resilient action of

the spring 19 maintains an interference fit retaining the trip plate 6 sandwiched therebetween. The trip plate also includes an aperture 24 for connection to the lanyard 7. The notches 21,22,23 also act to prevent the trip plate 6 from being inadvertantly dislodged by rotation from between the contact block 12 and the boss 11.

The preferred embodiment disclosed in International Application No. PCT/AU90/000181 included an electronics device having four batteries in which the contact pads 16 and 17 (see in Fig. 3 of the present specification ⁾ respectively connected to the terminals of two of each of the batteries. Accordingly, the contact pads 16 and 17 are C-shaped so as to provide interconnection 1n two configurations with respective pairs of battery terminals.

The embodiment shown in Figs. 4A and 4B illustrates .an alternative electrical device 40 having a switch assembly 50 including a contact block 51 which is used to provide switching for series aligned batteries 42.

The embodiment of Figs. 4A and 4B includes a switch boss 11 and spigot 13 corresponding to that already described. However, in this embodiment, the contact block 51 has a radial contact pad 52 and a peripheral contact pad 53, seen best In Fig. 4A. The contact pads 52 and 53, in a manner similar to the pads 16 and 17 of the block 12, are connected to a magnetically operable switch 54 arranged within the contact block 51.

As seen in Fig. 4B, the radial contact pad 52 connects centrally with a terminal of one of the batteries 42. The peripheral contact pad 53 is arranged to connect to a contact pin 43 biased onto the pad 53 via a spring 44. In this manner, the switch assembly 50 of Fig. 4B can be switched in a manner similar to the assembly 10 by rotating the switch boss 11 in the usual manner. For emergency operation, as in International Application No. PCT/AU90/00181 , the switch boss 11 and contact block 51 are rotated together (i.e. without extracting the posts 14 and 15 from the block 51) which thereby displaces the radial contact pad 52 and the peripheral contact pad 53. With a rotation of 90°, the radial contact pad 52 turns to make contact with the contact pin 43 thereby providing an interconnection which by-passes the magnetically operable switch 54.

There can be any number of batteries 42 arranged in series connection and the other terminal of the batteries, interconnects with a contact pad 46 mounted on a spring 47. The contact pin 43 extends through a passage 45 (illustrated in phantom) to provide a terminal connection 49 associated with a terminal connection 48 from the contact pad 46. The terminal connections 48 and 49 can thereby mate to any form of electrical load 60 such as lamp, electronics package such as a radio frequency transmitter and the like. The load 60 need not be confined within the casing 41 of the device 40. In view of the common arrangement of the switch boss 11 between the embodiments of Fig. 3 and Fig. 4, the trip plate 6 is also useful in providing trip activation of the electrical device 40 of Figs. 4A and 4B.

It will the apparent to those skilled in the art that the present invention can be used in configurations other than with life rafts. For example, military organisations can use trip plate activation to detect disturbances to "trip wires" for security purposes. ^" In such embodiments, the electrical devices, can be either light emitting or infrared flashing lamps, or explosive charges for example. The foregoing describes only two embodiments of the present invention and modifications, obvious to those skilled in the art can be made thereto without departing from the scope of the present invention.

For example, the shape and configuration of the trip plate 6 can be varied according to any design variations of the switch boss 11 and contact blocks 12,51..