GB2112211A

GB2112211A - Electric switch

Info

Publication number: GB2112211A
Application number: GB08236683A
Authority: GB
Inventors: R J Reid
Original assignee: KAC Alarm Co Ltd
Current assignee: KAC Alarm Co Ltd
Priority date: 1981-12-23
Filing date: 1982-12-23
Publication date: 1983-07-13
Also published as: GB2112211B

Abstract

A switch for use in a fire alarm system has electrical contacts (13-15) urged to an unoperated condition by springs (18) and a further spring (25) which normally acts on a glass or resiliently deformable member (24). If the member (24) is broken or deformed, force is transmitted from the spring (25) to a pivotable driving element (19) to cause the contacts to be operated and maintained in an operated condition against the action of the springs (18). To test the switch, a support (22) for the plate (24) can be pivoted so as to move the plate (24). If the member (24) is formed of or contains thermoplastic material, the springs (25) will cause automatic actuation at elevated temperatures. <IMAGE>

Description

SP ECIFICATION Electric switch This invention relates to an electric switch and is primarily concerned with a switch of the kind used in alarm systems, having electrical contacts which normally remain in an unoperated condition, which can be charged to an operated condition by manual application of pressure of a surface of the switch. which remain in the operated condition which the switch is relieved of the manually applied pressure and which can subsequently be set to the unoperated condition.

Generally, setting to the unoperated condition so that the unoperated condition is maintained involves replacement of a glass or other frangible member which is necessarily broken by the application of the pressure to the switch to cause the contacts to assume the operated condition.

One disadvantage of known switches of the kind referred to is that reliance is placed upon a spring to establish the operated condition of the contacts. If movement of the contacts should be obstructed, for example by fragments of broken glass or by the accumulation of foreign matter over a number of years, or the spring should deteriorate during the service life of the switch, the spring may fail to establish the operated condition of the contacts.

According to a first aspect of the invention, there is provided a switch comprising a body, electrical contacts having an operated condition and an unoperated condition, a driving element movable relative to the body when the contacts are in the unoperated condition for establishing the operated condition of the contacts, biasing means for yieldably resisting a change in the condition of the contacts and an intermediate element having a surface accessible to the hand of a user, being arranged to transmit pressure exerted on said surface to the driving element to establish the operated condition of the contacts and being so arranged that the exertion by the user on said surface of a force which is sufficient to establish the operated condition of the contacts so deforms the intermediate element that the deformation is not automatically reversed completely when the user ceases to exert said force on said surface.

In use of a switch according to the first aspect of the invention, the user can force the contacts into the operated condition. In most cases in accordance with the invention, the force exerted by a user on the surface of the intermediate element serves partly to stress the intermediate element and is only partly transmitted to the driving element, at least until the intermediate element yields completely, for example is broken.

The intermediate element is preferably of a frangible nature. The deformation of the intermediate element caused by operation of the switch is preferably a permanent deformation, for example breakage of the intermediate element.

According to a second aspect of the invention, there is provided a switch comprising a body, electrical contacts having an operated condition and an unoperated condition, a driving element movable relative to the body when the contacts are in the unoperated condition for establishing the operated condition of the contacts, a resilient member arranged to be capable of exerting on the driving element a force to establish the operated condition of the contacts and an intermediate element arranged to bear at least a part of said force so that, whilst the intermediate element is effective, the resilient member is prevented from establishing the operated condition of the contacts, the intermediate element being adopted to be deformed by manual application of pressure on a surface of the switch in a manner such that it ceases to bear said force or a part thereof and allows the resilient member to establish the operated condition of the contacts and such that the intermediate member remains deformed when said application of pressure ceases.

An example of a switch embodying both aspects of the invention will now be described, with reference to the accompanying drawings, wherein: FIGURE 1 illustrated diagrammatically a perspective view of the switch from above, parts of the switch being broken away to reveal internal parts; and FIGURE 2 is a perspective view of certain parts from below the switch.

The switch comprises a body including an upper body part 10 and a lower body part 11. The upper body part has the form of a rectangular frame and is hinged to the lower part and secured by a screw (not shown) by screws 12. For convenience of manufacture and assembly of the switch, the lower body part may comprise a plurality of separately formed components.

The lower body part II has the form of an opentopped box and there is mounted on an underside of bottom wall 9 of the lower body part a first pair of fixed, electrically conductive contacts 13 and a further pair of contacts 1 4, spaced upwardly from the contacts 1 3. There is associated with each of the contacts 13 and 1 4 a respective terminal which is accessible at the underside of the body. A housing 8 which contains the contacts is partly broken away in Figure 2.A movable contact 1 5 is carried on a movable contact carrier 1 6 (shown in Figure 1) for movement between an unoperated condition, in which the movable contact bridges the contacts 14, and an operated condition in which the movable contact 1 5 bridges the contacts 13 and is spaced from the contacts 1 4.

The contact carrier 16 is slidable through the bottom wall 9 of the lower body part Il and normally projects above the bottom wall. The contact 1 5 is biased to its unoperated condition by a pair of coiled springs 1 8 disposed within the housing 9 and acting between the housing and lateral, nonconducting extensions of the contact carrier.

For transmitting to the upper end of the contact carrier 1 6 force acting in a direction towards the bottom wall 9 and thus operating the contacts, there is provided a driving element 1 9. The driving element is generally of plate-like form and extends at a level above the lower body part II over a major portion of that body part, as viewed in plan. The driving element is pivotally connected with the lower body part for relative movement about an axis 20 which is parallel to the bottom wall 9 and to an end wall 21 of the lower body part and is situated near to an opposite end wall of the lower body part.The driving element 1 9 normally rests on the upper end of the contact carrier 1 6 and the contact carrier is spaced substantially from the axis 20, so that the part of the driving element which engages the contact carrier moves approximately in the direction of movement of the contact carrier.

The switch further comprises an intermediate element 24 in the form of a plate which overlies the driving element 1 9 and is trapped between the driving element and the upper body part 10. The upper body part overlies marginal portions of the plate. A marginal portion of the plate 24 adjacent to the end wall 21 extends beyond the corresponding margin of the driving element 19 and rests on a support 22. This support is mounted in the lower body part II for pivoting relative thereto about an axis 23 which is parallel to the axis 20. The support 22 is eccentric with respect to the axis 23 so that, upon pivoting of the support from the position illustrated in the drawing, the marginal portion of the plate 24 which rests on the support is permitted to move towards the bottom wall 9.The plate 24 rests at its end remote from the wall 21 on the driving element 1 9 but the intervening part of the plate is spaced slightly from the driving element when the support 22 is in the position shown in the drawing.

A major proportion of the upper surface of the plate 24 is exposed within a central opening defined by the upper body part 1 0 and is therefore accessible to the hand of a user. The plate has a character such that the exertion of moderate pressure, by hand, on the exposed part of the plate will deform the plate in such a manner that the deformation is not automatically reversed completely when the user ceases to exert the force on the plate.Furthermore, the deformation of the plate is sufficient to enable the plate to transmit at least a major part of the force exerted thereon to the driving element 1 9 at a position lying within the central opening defined by the upper body part 1 0. Typically, the plate 24 is formed of a frangible material;for example glass, and is weakened by a transverse score on its underside.so that it will break when moderate pressure is exerted on the middle of the plate.

The plate 24 is adapted to break, when subjected to pressure by a user, along a line extending generally parallel to the axis 20, rather than perpendicular to that axis. Accordingly, the plate preferably has a length extending in a direction perpendicular to the axis 20 which exceeds its width measured in a direction parallel to that axis.

If a user exerts on the middle of the exposed surface of the plate 24 a force which is sufficient to break the plate and continues application of that force, at least momentarily, after the plate has broken, the force will be transmitted by the broken plate to the driving element 1 9 and thence to the contact carrier 1 6 to bring about operation of the contacts, against the action of the springs 1 8. It will be noted that reliance is not placed upon springs to bring about operation of the contacts.

Resilient means in the form of a coiled spring 25 is provided for maintaining the contacts in the operated condition after the application of hand pressure to the broken plate 24 ceases. The spring 25 is mounted within the upper body part 10 to overlie marginal portions of the plate 24 and driving element 1 9. In the unoperated condition of the switch, the force exerted by the spring 25 is borne by the plate 24 and this force is insufficient to deform the plate.When the plate has been broken or otherwise deformed, the plate transmits to the driving element 1 9 the force exerted by the spring 25 and this force is sufficient to maintain the contacts in the operated condition, against the action of the springs 1 8. It will be understood that, if the plate 24 is broken by a user but the user does not exert force on the plate after it has been broken, so that the user does not operate the contacts, the spring 25 will overcome the action of the springs 1 8 and operate the contacts. A plurality of springs 25 may be provided.

We have found that the provision of separate springs, one or more to oppose operation of the contacts whilst the plate 24 remains undeformed, and the other spring or springs to establish or maintain the operated condition of the contacts after the plate 24 has been broken contributes to the provision of a reliable switch at moderate cost.

Furthermore, when the upper body part 10 is removed from the lower body part to enable a new plate 24 to be inserted in place of the broken plate, the spring 25 is removed with the upper body part and the springs 1 8 are able to establish the unoperated condition of the contacts once more without hindrance. The provision of the separate springs 18 and 25 also faciiitates testing of the contacts.

To enable operation of the contacts to be tested, an aperture 26 is provided in the end wall 21 adjacent to one end of the support 22 and a coupling element 27 is provided on the support to project from this end of the support in a direction parallel to, but offset from, the axis 23. The coupling element 27 is aligned with the aperture 26 so that a tool 28, a part only of which is shown, can be inserted through the aperture to couple with the element. By means of the tool, the support can be pivoted about the axis 23 to permit the plate 24 to be moved towards the bottom wall 19 underthe action of the spring 25 sufficiently for the contacts to be operated.

The tool is so formed that, when an attempt is made to withdraw it from the body, the support 22 is pivoted to its initial position before the tool becomes uncoupled from the coupling element 27 and withdrawn from the body. Pivoting of the support in the absence of the tool is resisted by the spring 25 which urges the place 24 against a flat surface on the support. If required, there may be provided a leaf spring which opposes pivoting of the support 22 in the absence of the tool and which is displaced by the tool to permit pivoting of the support.

The plate 24 may have a laminated construction, comprising a layer of relatively rigid and brittle material, for example glass, and a layer of relatively flexible material, for example a thermoplastics material. A plate of this laminated construction is not completely broken into fragments when pressure is exerted on its exposed face but the plate is so deformed that it is no longer capable of bearing a substantial part of the load exerted by the springs 25.

A further alternative form of intermediate element presents a convex surface outwardly of the switch and is formed of resilient material having a strength and thickness such that it can normally bear the load exerted by the spring 25 but, when additional load is exerted on the intermediate element by a user, it is deformed to present a concave surface outwardly of the switch and in this deformed configuration no longer relieves the driving element 1 9 of the load exerted by the spring 25.

It will be noted that each of the aforementioned forms of intermediate element is incapable of resuming automatically its initial configuration when relieved of pressure exerted by a user on the exposed face of the intermediate element. Once the intermediate element has been deformed by a user, it remains deformed, until the upper body part 10 is removed and the intermediate element is either replaced or returned to its initial configuration.

The character of the intermediate element 24 is such that breakage or other non-spontaneously reversible deformation of the intermediate element is inevitably caused when a user exerts on the exposed surface of the intermediate element a force which operates the contacts. Accordingly, whenever the contacts are operated by a user pressing on the intermediate element, the appearance of the intermediate element will be changed substantially and the fact that the contacts have been operated will be readily apparent.

In a case where the plate 24 is formed of a thermoplastics material or incorporates a thermoplastics material from which a substantial part of the strength of the element is derived, the intermediate element will be incapable of bearing a substantial part of the load exerted by the springs 25 at elevated temperatures. Thus, the contacts of the switch would be operated automatically in the event of a fire which causes the temperature of the switch to rise substantially above normal ambient temperatures.

There may be provided in the switch a diaphragm which seals the top of the lower body part II against ingress of foreign matter, for example dust or moisture, the diaphragm being capable of flexing to accommodate movement of the plate 24, driving element 1 9 and contact carrier 1 6. In a case where a diaphragm is provided, there may also be provided a removable plug of the aperture 26.

Claims

1. A switch comprising a body, electrical contacts having an operated condition and an unoperated condition, a driving element movable relative to the body when the contacts are in the unoperated condition for establishing the operated condition of the contacts, biasing means for yieldably resisting a change in the condition of the contacts and an intermediate element having a surface accessible to the hand of the user, being arranged to transmit pressure exerted on said surface to the driving element to establish the operated condition of the contacts and being so arranged that the exertion by the user on said surface of a force which is sufficient to establish the operated condition of the contacts so deforms the intermediate element that the deformation is not automatically reversed completely when the user ceases to exert said force on said surface.

2. A switch comprising a body, electrical contacts having an operated condition and an unoperated condition, a driving element movable relative to the body when the contacts are in the unoperated condition for establishing the operated condition of the contacts, a resilient means arranged to be capable of exerting on the driving element a force to establish the operated condition of the contact and an intermediate element arranged to bear at least a part of said force so that, whilst the intermediate element is effective, the resilient means is prevented from establishing the operated condition of the contacts, the intermediate element being adapted to be deformed by manual application of pressure on a surface of the switch in a manner such that it ceases to bear said force or a part thereof and allows the resilient means to establish the operated condition of the contacts, and such that the intermediate member remains deformed when said application of pressure ceases.

3. A switch according to Claim 2 further comprising biasing means for yieldably resisting a change in the condition of the contacts and wherein the intermediate element has a surface accessible to the hand of a user, is arranged to transmit pressure exerted on said surface to the driving element to establish the operated condition of the contacts, and is so arranged that the exertion by the user on said surface of a force which is sufficent to establish the operated condition of the contacts so deforms the intermediate element that the deformation is not automatically reversed completely when the user ceases to exert said force on said surface.

4. A switch according to Claim 2 or Claim 3 wherein the body comprises two relatively movable parts, the contacts are mounted in a first of said parts and the resilient means is carried by a second of said parts.

5. A switch according to any one of Claims 2 to 4 further comprising a support and wherein the intermediate element is urged onto the support by the resilient means and the support is movable relative to the body in a manner to permit limited movement of the intermediate element which is sufficient to allow the resilient means to cause the contacts to assume the operated condition.

6. A switch according to Claim 5 wherein the support is pivoted on the body.

7. A switch according to Claim 5 or Claim 6 wherein the intermediate element is of plate-like form and the support is adjacent to a margin of the intermediate element.

8. A switch according to any preceding claim wherein the intermediate element is frangible.

9. A switch according to any preceding claim wherein the driving member is mounted for pivoting relative to the body.

1 0. A switch according to any preceding claim further comprising a contact carrier which carries one or more of said contacts, is movable relative to the body and is engageable with the driving member.

11. A switch according to Claim 1 further comprising a support and resilient means so arranged that the intermediate member is urged onto the support by the resilient means and wherein the support is movable relative to the body in a manner to permit limited movement of the intermediate member which is sufficient to allow the resilient means to cause the contacts to assume the operated condition.

12. A switch according to Claim 11 wherein the support is pivoted on the body.

13. A switch substantially as herein described with reference to and as shown in the accompanying drawing.

14. Any novel feature or novel combination of features disclosed herein or in the accompanying drawing.