GB2206240A

GB2206240A - Magnetically operated electrical switches

Info

Publication number: GB2206240A
Application number: GB08814860A
Authority: GB
Inventors: Eric Franklin Birns
Original assignee: BIRNS UK Ltd
Current assignee: BIRNS UK Ltd
Priority date: 1987-06-26
Filing date: 1988-06-22
Publication date: 1988-12-29
Also published as: GB8814860D0; GB8715089D0

Abstract

An electrical switch comprises a microswitch (30) mounted in a first chamber (18) of a casing (10). A first magnet (32) is located adjacent the actuating member (34) of the microswitch (30) and may be urged against the actuating member (34) by magnetic repulsion when a second magnet (54) is moved into proximity therewith by movement of a sliding plunger (56). The microswitch (30) is mounted in a holder including springs for biasing the magnet (32) to its non-actuating position, or bias is provided by the microswitch mechanism. The second magnet (54) can be biassed by magnetic repulsion alone and can be mounted in its own housing which is sealed or not to the environment. The switch is suitable for installation in bulkheads or the like to serve as a control switch in hostile environments since there is no mechanical linkage between the plunger (56) and microswitch (30). <IMAGE>

Description

Improvements in or relating to Electrical Switches The present invention relates to an improved actuating mechanism for electrical switches and is particularly, but not exclusively, concerned with control or limit switches for use in hostile environments.

Where an electrical switch is to be used in a hostile environment, it is desirable that the switch itself be isolated from its surroundings both to ensure reliable operation of the switch and for safety considerations.

Accordingly, if a mechanical actuating linkage is required to extend through a bulkhead or the like to operate a switch, difficulties are encountered.in maintaining effective seals. Electronic proximity sensors are also subject to interference problems when operating in radioactive environments.

It is an object of the present invention to obviate or mitigate the aforesaid disadvantages.

Accordingly, the invention provides an electrical switch comprising electrical switching means having an actuating member and a first permanent magnet movably located adjacent said actuating member such that said magnet may be urged against the actuating member to actuate said switching means in response to the proximity of an opposed magnetic field.

Preferably, said switching means and said first permanent magnet are located in a first, closed chamber.

Preferably also, the switch further includes a second permanent magnet movable into and out of proximity with said first magnet, the first and second magnets being arranged with like poles facing one another.

Preferably also, said second magnet is located in a second chamber and is movable in response to operation of a further actuating means.

Preferably also, said first and second chambers are formed in a common housing, said first and second magnets being located on either side of a wall separating the two chambers. The housing may be adapted to extend through a bulkhead or the like. Alternatively, the first and second chambers may be formed in independent housings.

The mechanism of the invention thus provides an actuating mechanism wherein the switch may be completely isolated from its surroundings without the need for mechanical linkage or sensitive electronic components and will thus operate reliably in hostile environments and will not be adversely affected by radio-activity.

An embodiment of the invention will now be described by way of example only, with reference to the accompanying drawings in which, Fig. 1 is a sectional side view of a switch housing embodying the invention; Figs. 2(a) and 2(b) are, respectively side and end views of a microswitch mounted in a holder forming part of the housing of Fig. 1; Fig. 3 is a sectional side view of an alternative embodiment of the invention; and Fig. 4 is a sectional side view of still another embodiment of the invention.

Referring now to the drawings, a switch housing 10 comprises a generally cylindrical casing 12 having a first, relatively narrow, externally threaded portion 14 and a second, wider portion 16. It will be appreciated that this external shape may be varied widely as desired or as required by particular circumstances. The portion 16 may be externally shaped to accept a spanner or the like by provision of flat portions (not shown) on its external surface or by being made hexagonal in section.

Alternatively, the casing 12 may be of a constant diameter and be externally threaded along its entire length. Axial bores extending inwardly from either and of the casing 12 define first and second chambers 18 and 20 separated from one another by a wall 22.

The first chamber 18 is closed and sealed by an end plug 24, having electrical terminals 26 extending therethrough, and encloses a commercially available microswitch 28, mounted in a substantially cylindrical holder 30 located adjacent the end plug 24 and connected to the terminals 26 and a first disc-shaped permanent magnet 32 slidably located between the microswitch 28 and the wall 22.

The actuating member 34 of the microswitch 28 faces the first magnet 32.

The microswitch 28 is positioned in a diametrical slot formed in the holder 30 and is retained by a pair of pins (not shown) extending through corresponding pairs of apertures 36 in the holder 30 and microswitch 28. First and second bores 38 and 40 are formed in the end face 42 of the holder 30 on either side of the microswitch 28, wherein are located first and second coil springs 44 and 46 which, in use, serve to bias the first magnet 32 away from the actuating member 34 of the microswitch 28.

The second chamber 20 is a free-flooding chamber having an end piece 48 provided with a central aperture 50 through which an elongate actuating plunger 52 passes. A second disc-shaped permanent magnet 54 is attached to the inner end of the plunger 52 within the second chamber 20 and a stop member 56 is attached to the opposite, outer end thereof. The second magnet is thus slidable between a first position adjacent the end piece 48 and a second position adjacent the wall 22, and is biased towards said first position by a third coil spring 58 located on the plunger 52 between the end piece 48 and the stop member 56.

The first and second magnets 32 and 54 are arranged in the housing 10 with like poles facing one another such that when the plunger 52 is depressed against the force of the spring 58 and the second magnet 54 is moved from its first to its second position, the first magnet 32 is repelled and urged against the actuating member 34 to operate the microswitch 28. When the plunger 52 is released the second magnet 54 returns to its first position and the first magnet 32 releases the microswitch 28.

The arrangement allows the microswitch 28 to be completely isolated from its surroundings with no physical connection to the actuating plunger 52, and is thus suitable for use as a control or limit switch in a hostile environment; eg underwater. The device described is suitable for installation in a bulkhead or the like. In some situations it may be desirable to prevent the ingress of debris into the second chamber 20, so as to avoid fouling of the plunger 52, in which case the second chamber may be closed by a bellows arrangement or the like between the casing 12 and the plunger 52.

Fig. 3 shows a modification of the switch housing of Fig. 1, again having a casing 60 divided into first and second chambers 62 and 64 separated by a wall 66, a microswitch 68 and a first permanent magnet 70 located in the first chamber 62 and an actuating plunger 72 and a second permanent magnet 74 located in the second chamber 64.

In this case the second chamber 64 is closed at its outer end by a jam nut 76 and snap ring 78. The plunger 72 is provided with an axial bore 80, closed at the outer end thereof, and is in telescopic engagement with a hollow tubular guide member 82 projecting rearwardly from the wall 66, the second permanent magnet 74 being annular and slidable along the exterior surface of the guide member 82.

The plunger 72 and second magnet are biased into the first position (away from the wall 66 as before) by a spring 84 located inside the plunger 72 and guide member 82 and abutting the outer end of the bore 80 and the wall 66. This replaces the externally mounted spring 58 of Fig. 1 which might be vulnerable to the accumulation of debris.

Fig. 4 shows a further embodiment of the invention, having a casing 86, first and second chambers 88, 90 and a dividing wall 92. The microswitch 94 is again mounted in a holder 96 located in the first chamber 88, and the first magnet 98 is located between the microswitch 94 and wall 92 in a bore formed in the holder 96. The second magnet 100 is mounted in a thickened end of cylindrical plunger 102, which is slidable within the second chamber 90 and is retained in place by a tube 104 located in the second chamber 90 adjacent the outer end thereof. Channels 106, 108 may be formed in the outer walls of the second chamber 90, allowing the interior thereof to communicate with the external environment.

This embodiment differs from those of Figs. 1 and 3 in that no additional biasing springs are included. Instead, the internal biasing of the microswitch actuating member serves to bias the first magnet 98 whilst the mutual repulsion of the magnets 98, 100 biases the plunger and second magnet 100.

Since there is no mechanical linkage between the actuating plunger 52, 72 or 102 and the microswitch 28, 68 or 94, the first and second chambers 18, 62 or 88 and 22, 64 or 90 need not be formed in a common casing but could form discrete units. Thus, the microswitch 28, 68 or 94 and first magnet 32, 70 or 98 may be located in a first unit which might be positioned on one side of a bulkhead and the second magnet 54, 74 or 100 and actuating means located in a second unit positioned on the opposite side of the bulkhead so that the need for an aperture formed in the bulkhead is eliminated. Obviously, the microswitch will be responsive to any opposed magnetic field coming into proximity with the first magnet 32, 70 or 98 so that the actuating arrangement may be varied from the plunger mechanism illustrated.

The materials from which the housing is constructed will depend upon the nature of the environment in which it is intended to operate. In a radio-active environment, for example, organic materials should be avoided and the casing 12, 60 or 88 should be of an alloy resistant to radioactivity so as to avoid problems such as the binding of screw threaded parts. Obviously, the dimensions of the casing and the sizes and strengths of the magnets will depend on the particular application.

Claims

1. An electrical switch comprising electrical switching means having an actuating member and a first permanent magnet movably located adjacent said actuating member such that said magnet may be urged against the actuating member to actuate said switching means in response to the proximity of an opposed magnetic field.

2. An electrical switch as claimed in claim 1, further including a second permanent magnet movable into and out of proximity with said first magnet, said first and second magnets being arranged with like poles facing one another.

3. An electrical switch as claimed in claim 2 wherein said switching means and said first magnet are located in a first, closed chamber.

4. An electrical switch as claimed in claim 3 wherein said second magnet is located in a second chamber and is movable in response to a further actuating means.

5. An electrical switch as claimed in claim 3 or claim 4 wherein said first and second chambers are formed in a common housing, said first and second magnets being located on either side of a wall separating the two chambers.

6. An electrical switch as claimed in claim 5 wherein said housing is adapted to extend through a bulkhead or the like.

7. An electrical switch as claimed in claim 3 or claim 4 wherein said first and second chambers are formed in independent housings.

8. An electrical switch as claimed in any of claims 4 to 7 wherein said further actuating means comprises a member slidable within said second chamber and having said second magnet attached thereto.

9. An electrical switch as claimed in claim 8 wherein said member is biased towards a first position wherein said second magnet is out of proximity with said first magnet.

10. An electrical switch substantially as hereinbefore described with reference to Figs. 1, 2(a) and 2(b).

11. An electrical switch substantially as herein before described with reference to Fig. 3.

12. An electrical switch substantially as herein before described with reference to Fig. 4.