GB2352332A - Trigger mechanism for an alarm call-point - Google Patents

Abstract

A trigger mechanism for an alarm call-point, has a manually operable pressure plate 17, a switch actuator 37, and a visual indicator means (33, Fig.5) to provide a visual indication that the alarm has been triggered, wherein the trigger mechanism may be used in conjunction with a frangible type alarm call-point so as to convert it to a non-frangible type.

Description

2352332 Title: A Trigger Mechanism for an Alarm Call-Point Descrintion of

Invention This invention relates to a trigger mechanism for an alarm call-point, wherein the term "call-point" is used to refer to a manually operable alarm switch of the kind which is activated by a user in response to a fire or other such incident.

Known call-points are usually mounted in a wall mounted box having a front face provided with a frangible element, such as a glass window, which is broken when activation of the alarm to which the call-point is connected is required. Henceforth, call-points of this kind are referred to as "call-points of the frangible type."

In view of safety considerations, other call-points exist which are provided with a non-frangible element, which deforms generally elastically upon application of pressure by an operator, which, as the element is left substantially intact after operation, may then be reset for subsequent use. Such call-points are referred to hereinafter as "call- points of a non-frangible type."

- It is an object of the present invention to provide an improved trigger mechanism for alarm call-points.

According to a first aspect of the present invention, there is provided a trigger mechanism for an alarm call-point comprising a manually operable pressure plate capable of being moved from an inactivated to an activated position, a switch actuator operatively associated therewith, which is biased towards an actuated position, movement of the switch actuator towards said actuated position being resisted when the pressure plate is in its inactivated position.' but permitted when the pressure plate is moved to its activated position such that an alarm to which the callpoint is operatively connected may be triggered, mechanically operable means being provided, which on triggering 2 of the alarm, provides a visual indication that the alarm has been triggered, the visual indicator means also being operatively associated with the pressure plate; characterised in that the trigger mechanism may be used in conjunction with an alarm call-point of the frangible type, such that by removing its frangible plate and by attaching the trigger mechanism to the call-point, the call-point may be converted from a frangible to a non-frangible type.

The switch actuator and the visual indicator means may be carried by a carrier member, the carrier member being provided with a stop co-operable with an engagement part of the pressure plate. In this way, movement of the pressure plate towards its activated position may cause said stop and engagement part to move out of engagement such that the carrier member may move towards an activated position under the action of resilient biasing means.

Preferably, the carrier member is generally planar, with the stop conveniently being provided by a raised formation extending out of the plane.

The engagement part of the pressure plate may be provided by a lug, tab or the like, conveniently extending from an operative edge portion thereof.

The pressure plate, in its inactivated position, preferably overlies a leading edge portion of the carrier member.

The switch actuator may comprise a raised formation such as a pin, which on movement towards its actuated position, may be guided through a channel or recess provided in the operative edge portion of the pressure plate.

The visual indicator means may be provided on or by the leading edge portion of the carrier member, and the visual indicator means may therefore be generally planar.

According to a second aspect of the present invention, there is provided an alarm call-point comprising a trigger mechanism in accordance with the first aspect of the invention.

3 According to a third aspect of the present invention, there is provided a method of converting an alarm call-point of the frangible type to an alarm callpoint of a non-frangible type, comprising removing the frangible plate from the frangible-type alarm call-point, and attaching thereto a trigger mechanism comprising a manually operable pressure plate capable of being moved from an inactivated to an activated position, a switch actuator operatively associated therewith, which is biased towards an actuated position, movement of the switch actuator towards said actuated position being resisted when the pressure plate is in its inactivated position, but permitted when the pressure plate is moved to its activated position such that an alarm to which the call-point is operatively connected may be triggered, mechanically operable means being provided, which on triggering of the alarm, provides a visual indication that the alarm has been triggered, the visual indicator means also being operatively associated with the pressure plate.

The trigger mechanism may be provided with a reset feature, whereby introduction of a reset tool such as a key enables the switch actuator to move away from its actuated position towards a non-actuated position, and the pressure plate to move back towards its inactivated position.

The invention will now be described by way of example only, with reference to the accompanying drawings, of which:

Figure I is a perspective view, from the rear, of the trigger mechanism in a "set" condition, shown without a cover part, Figure 2 shows the arrangement of Figure 1, with the cover part attached, Figure 3 shows a similar perspective view as that of Figure 1, but with the trigger mechanism "activated", Figure 4 shows a view similar to that of Figure 3, with the cover part, Figure 5 is a plan view of the front of the trigger mechanism, shown in its activated position, 4 Figure 6 is a perspective view, from the front, of a conventional glass (frangible) call-point, and Figure 7 shows the trigger mechanism of the present invention, in a 'set' condition, in co-operation with the call-point of Figure 5, with the glass plate removed.

Referring first to Figure 1, the trigger mechanism generally indicated at 10 is provided within a housing 11, the housing comprising an apertured base 12 and side walls 13, 14, 15 and 16 upstanding therefrom. The trigger mechanism comprises a generally planar pressure plate 17 mounted for pivotal movement at its base 18 by a pair of feet 19 which co-operate with a pair of generally U-shaped posts 20 upstanding from the base 12. The pressure plate 17 is biased towards the base 12 by a pair of compression springs 21 mounted about a pair of posts 21,a which upstand from a rear face of the pressure plate 17. As shown in Figure 2, these springs act upon an inside face of a cover 22, which is held in position by recessed posts 23 and screws 24 which engage with internally threaded pillars 25.

The trigger mechanism also comprises a generally planar carrier member 28 which is biased downwardly, from the position shown in Figure 1, to the position shown in Figure 3, by a compression spring 29, one end of which bears upon an inwardly facing surface of the side wall 13, the other end of which bears upon the inside of a recess 30 in an upper edge portion 31 of the carrier member 28.

The carrier member 28 is provided with two upstanding formations in the form of relatively shallow blocks 32, which, in the condition shown in Figure 1, bear upon a pair of tabs 27 which extend from the operative edge portion 26 of the pressure plate 17. It will be appreciated that in view of the downward bias applied to the pressure plate 17 by the compression springs 2 1, the blocks 32 and tabs 27 are maintained in generally face-to-face abutting relationship, which prevents movement of the carrier member 28 under the action of compression spring 29.

As shown in Figures 1, 3 and 5, a leading edge portion 33 of the carrier member is coloured, marked, or otherwise adapted to be readily visible once activation of the trigger mechanism has occurred. As will be appreciated especially from Figures 3 and 5, subsequent to such activation, the leading edge portion 33 extends into the aperture 34 provided in the base 12, thus providing an effective visual indication that the alarm to which the trigger mechanism is operatively connected has been activated.

Specifically, upon application of pressure to the outer face of the pressure plate 17, (acting against the bias of the compression springs 21) the pressure plate is caused to pivot about its base 18, which frees the tabs 27 and blocks 32 from their face-to-face engagement. This, in tam, allows the carrier member 28 to be moved downwardly (towards the position shown in Figures 3, 4 and 5) under the action of compression spring 29, thus causing the visual indicator provided by the leading edge portion 33 of the carrier member, to become visible from the front of the housing. As will be seen from Figures 2 and 4 especially, pivotal movement of the pressure plate causes the posts 2 la to partially enter into slots 22a provided in the cover part 22.

To minimise any risk of skewing of the carrier member during its movement from the position shown in Figure 1 to the position shown in Figure 3, the carrier member is provided with a pair of elongate legs 36 which extend alongside, and abut, the inner faces of the side walls 14 and 16 respectively.

The carrier member is also provided with a switch actuator 37 in the form of an upstanding post, which in use, bears upon a switch member 38 (see Figures 6 and 7) of the call-point to which the trigger mechanism is attached.

If will be appreciated that in the position shown in Figures 1, 2 and 7, the switch actuator presses against the switch member 38, maintaining the associated switch circuitry in an open condition, but that once the switch 6 actuator has moved to the position shown in Figures 3 and 4, the switch member is released, causing the alarm circuitry to adopt a closed condition, thus triggering the alarm, in conventional manner.

To enable the trigger mechanism to be reset, a cross-bar 39 is provided, which extends between the remote ends of the legs 36, the cross-bar being provided with a pair of transversely extending reset legs 40, which may be borne upon by prongs 41 of a reset key 42, which may be introduced to the housing through a pair of apertures 43.

It will be appreciated that in this way, the carrier member may be pushed back towards the position shown in Figures I and 2, and that the carrier member will become "latched" in this position due to re-engagement of its blocks 32 with the tabs 27 of the pressure plate 17, which is biased downwardly towards the carrier member by the compression springs 2 1.

Referring next to Figure 5, this shows a plan view of the trigger mechanism, wherein the visual indicator means 33, the carrier member 28 and the switch actuator are shown in their "released" positions. The front face 44 of the housing is provided with a through-bore 45 to receive a screw or similar fastening means, by which the trigger mechanism may be attached to the callpoint concerned, The front face is also provided with an aperture 46 for reception of an illuminating means such as a light emitting diode, which may additionally be used, if required, to provide a further visual indication of activation of the device, in regions of low illumination, for example.

Figure 6 shows a conventional frangible type call-point 50 of the type employing a frangible glass plate 51 to maintain a switch member 52 in a "set" position. It will be appreciated that sufficient pressure applied to the glass plate 51 by an operator will cause the plate to break, which in turn will free the switch -member 52, allowing it to move downwardly under the action of a spring in the direction shown by arrow W, enabling it to adopt a closed condition, thus triggering the alarm, in conventional manner.

7 Figure 7 illustrates how the trigger mechanism of the present invention may be used in conjunction with a known frangible type call-point of the type shown in Figure 6.

Specifically, it will be noted that the trigger mechanism is configured in such a manner that the switch actuator 37 abuts, in use, the switch member 52 of the call-point, and that with the trigger mechanism in the "set" condition shown, the switch actuator is operative to maintain the switch member 52 in an open condition, thus preventing triggering of the alarm.

When an inwardly directed force is applied to the pressure plate 17, however, the carrier member 28, with which is associated the switch actuator 37, is permitted to move generally downwardly, under the action of compression spring 29, freeing the switch member 52, and causing the alarm to be triggered. In addition, the leading edge portion 33 of the carrier member becomes visible through aperture 34, thus providing a readily apparent, and mechanically operated, visual indication of activation of the alarm.

As will be appreciated by those skilled in the art, a variety of materials may be used for construction of the trigger mechanism, although a relatively high density plastics material is likely to be particularly suitable.

In view of the fact that the trigger mechanism of the present invention is able to inter-fit with "existing" frangible type call-points, this enables such callpoints to be modified or upgraded should the use of a frangible material (such as glass) no longer be appropriate. Moreover, as the trigger mechanism provides a mechanically operable visual indication of activation of the alarm, the trigger mechanism of the present invention is able to comply with existing and expected European legislation.

The features disclosed in the foregoing description, or the following claims, 'or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any

8 combination of such features, be utilised for realising the invention in diverse forms thereof.

9

Claims (11)

1. A trigger mechanism for an alarm call-point comprising a manually operable pressure plate capable of being moved from an inactivated to an activated position, a switch actuator operatively associated therewith, which is biased towards an actuated position, movement of the switch actuator towards said actuated position being resisted when the pressure plate is in its inactivated position, but permitted when the pressure plate is moved to its activated position such that an alarm to which the call-point is operatively connected may be triggered, mechanically operable means being provided, which on triggering of the alarm, provides a visual indication that the alarm has been triggered, the visual indicator means also being operatively associated with the pressure plate; characterised in that the trigger mechanism may be used in conjunction with an alarm call-point of the frangible type specified, such that by removing its frangible plate and by attaching the trigger mechanism to the call-point, the call- point may be converted from a frangible to a non-frangible type.

2. A trigger mechanism according to claim I wherein the switch actuator and the visual indicator means are carried by a carrier member, the carrier member being provided with a stop co-operable with an engagement part of the pressure plate, the arrangement being such that movement of the pressure plate towards it activated position causes said stop and engagement part to move out of engagement such that the carrier member may move towards an activated position under the action of resilient biasing means.

3. A trigger mechanism according to claim 2 wherein the carrier member is generally planar, and the stop is provided by a raised formation extending out of the plane.

4. A trigger mechanism according to claim 2 or claim 3 wherein the engagement part of the pressure plate is provided by a lug, tab or the like, extending from an operative edge portion thereof.

5. A trigger mechanism according to claim 2, claim 3 or claim 4 wherein the pressure plate, in an inactivated position, overlies a leading edge portion of the carrier member.

6. A trigger mechanism according to any one of the preceding claims wherein the switch actuator comprises a raised formation such as a pin, which on movement towards its actuated position, is guided through a channel or recess provided in an operative edge portion of the pressure plate.

7. A trigger mechanism according to claim 5 or claim 6 wherein the visual indicator means is provided on or by the leading edge portion of the carrier member.

8. A trigger mechanism substantially as hereinbefore described and/or as shown in the accompanying drawings.

9. An alann call-point having a trigger mechanism in accordance with one or more of the preceding claims.

10. A method of converting an alarm call-point of the frangible type to a non-frangible type alarm call-point comprising removing its frangible plate and attaching to the call-point a trigger mechanism comprising a manually operable pressure plate capable of being moved from an inactivated to an activated position, a switch actuator operatively associated therewith, which is biased towards an actuated position, movement of the switch actuator towards said actuated position being resisted when the pressure plate is in its inactivated position, but permitted when the pressure plate is moved to its activated position such that an alarm to which the call-point is operatively connected may be triggered, mechanically operable means being provided, which on triggering of the alarm, provides a visual indication that the alarm has been triggered, the visual indicator means also being operatively associated with the pressure plate.

11. Any novel feature or novel combination of features described herein and/or in the accompanying drawings.