GB1574703A

GB1574703A - Alarm call point

Info

Publication number: GB1574703A
Application number: GB4934875A
Authority: GB
Original assignee: EMI Ltd
Current assignee: EMI Ltd
Priority date: 1977-03-01
Filing date: 1977-03-01
Publication date: 1980-09-10

Description

(54) ALARM CALL POINT (71) We, E.M.I LIMITED, a British Company of Byth Road, hayes, Middlesex, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement : - This invention relates to an alarm call.

point including an alarm switch.

Call-point switches useful in setting off fire and other alarms in case of emergency and having a breakable front plate which retains unbroken a switch control element against change of condition are well known. While glass or other easily breakable materials are used for the front plates these are still not always easy to break by hand in case of emergency and even then there is a possibility that broken pieces of front plate can retain the switch control element preventing the switch from setting off the alarm. Proposals have been made (UK Patent Specifications 1103457 and 1311696) for the provision of anvils in the switch assembly to ease the breaking of the plate into pieces and for the use of a glass plate acting as a strut between an abutment and a microswitch control element. All these switch assemblies require several piece-parts and precise manufacture and assembly for successful operation.

It is an object of the invention to provide an improved alarm switch assembly.

According to the invention there is provided an alarm call point comprising a housing, a switch arrangement having an alarm condition mounted to the housing, an actuator movable with respect to the housing, resilient means for biassing the actuator, and a breakable element engaging the housing and capable of holding the actuator against the action of said biassing means so that the actuator engages the switch arrangement and prevents it from assuming the alarm condition, wherein said actuator substantially enclose the element within the housing and breakage of the element caused by movement of the actuator allows the switch arrangement to assume the alarm condition.

The actuator may be released from the alarm switch on the breaking of the element. The element may be a solid or hollow, body of glass or a plastics material.

Embodiments of the invention will now be described with reference to the drawings accompanying the Provisional Specification, in which: Figure 1 is a cross sectional side elevation of an alarm call-point switch assembly and Figure 2 shows a front elevation of the assembly of Figure 1, and to the accompanying drawings, in which: Figure 3 shows a plan view of another alarm call-point embodying the invention and Figure 4 and 5 show sectional elevations of the call-points of Figure 3.

Referring to Figures 1 and 2 the alarm callpoint switch assembly is contained in a box 1 which may be arranged for surface or recessed mounting on a wall, with fixing holes if needed and provided with a suitable cable entry for electrical conductors connected to the switch itself.

Within the box 1 is a wall 2 arranged to separate off the bottom or rear, as shown in the drawings, part of the box which contains the switch itself 3. The wall provides some protection against the entry of dirt, insects etc.

The wall is secured to supports 11 and has at its lower mid-point, as shown in the drawing, a recess 21. A matching slot 12 is provided in box 1 opposite this recess.

At the front of the box is an actuator in the form of a square plate 4 which is a loose fit in the aperture of the box. Plate 4 has a rib 41 extending from it and passing through an aperture 22 in wall 2. Rib 41 has a slot 42 matching slot 12 and recess 21 and, when assembled, aligned with them. A breakable element in the form of a glass strip 5 is passed through slots 12 and 42 into recess 21 on assembly of the alarm switch so that plate 4 is held in the assembly by glass strip 5. Rib 41 is formed with an extension 43 at one part.

.Reverting to switch 3 this consists of the two blades 31 and 32 carrying contacts in overlapping relationship at their outer ends.

,The blades are resilient and, in the absence of external action, are arranged to bring the contacts,into conductive connection. extension 43 of rib 41 is shaped to engage the rearward blade 32 and force it out of such connection against its resilience, so long as plate 4 is held in the assembled switch.

Guides 13 are provided on the wall 2 for rib 41 and an aperture 22 in wall 2 permits rib 41 to enter the rearward part of the box.

Items l, 2 and 4 can be moulded plastic piece parts without too tight tolerance being required. For assembly when the switch 3 has been installed in the box and connection made the wall 2 can be inserted and retained by snap engagement between suitably shaped parts of the plastics materials. The plate 4 can then be placed in position and the glass strip 5 inserted to hold the plate in position. The glass strip can be permanently secured in place if required or provision can be made for its removal by suitable "secret" means to permit testing of the switch connection.

To operate the assembled alarm switch the actuator, i.e. plate 4, is forced into the box byhaIzd pressure, flexing strip 5 until it breaks and it no longer holds the plate so that on release of the pressure on plate 4 further movement of the plate occurs by reason of switch resilience. This removes the restraint on the switch making connection and connection is made,-to give an alarm às required. After such operation the alarm switch may be restored by removing broken strip parts and inserting a fresh strip.

Various alternative arrangements are possible. The switch contacts are shown as held open for closure on salami but the reverse, ie held closed and opened on alarm, or change over contacts could be used. The strip of glass 5 could be replaced with a strip of a plastics material such as a crystalline styrene, or a rod instead of a strip. The plate 4 will usually fall clear of the box when strip 5 breaks, under the resilience of switch 3, but-this is not essential.

If required a ti,e or' say nylon thread, can be provided to secure the plate 4 to the box on the release of the plate. The plate 4 could have a knob so that it can be pulled out instead of pushed in. Alternatively the actuator could be pivotally mounted, eg as a lever or swinging plate. The pivot could be the breakable element.

To simplify connection with the switch, contacts may include one part of a receptacle-- and-tab connector, such as those available under the Registered Trade Mark FASTON.

The contact connector parts may be the tabs and may be inside or outside the box 1 eg in a recess in the outer wall to protect them.

A suitable plastics material for the assembly is polycarbonate, red for the box 1 and wall 2 and clear for the plate 4 to maintain conventional "break glass" call point appearance. The plate 4 can be marked PUSH if required and can be opaque if preferred.

The strip 5 may be of a brittle plastics material which melts at a temperature of about 80"C or above so that an alarm is automatically given if the call-point is close to a fire.

Details of the actual connections to the switch contacts are conventional other than as described with reference to the push-on receptacle-and-tab connectors. The plate 4 and wall 2 can be differently coloured so that there is a change of appearance on operation with release of the plate.

As mentioned above the assembly of the alarm switch can take place on installation at the point of use eg from kits of the piece parts involved, or the alarm switch can be supplied complete and tested. By assembling on site the need to dismantle to fix the box is avoided.

The construction of the breakable element in the alarm switch is particulary simple. The element is preferably of elongate form. If rod is used the only step is ,to cut it into lengths without any very close tolerance while the strip may be similarly produced without close tolerance. In the case of rod the diameter, which is the more significant dimension, is controlled during manufacture. The presence of the rib 41 assists in preventing broken pieces from jamming the plate 4 in place and preventing the operation of the alarm.

If required the plate 4 can have a flange or lip to loosely engage the box 1 to provide a seal against entry of dirt etc.

Alternatively wall 2 can be shaped to provide a lip all around the opening in box 1 into which plate'4 fits. The lip can have a resilient sealing material, such as a polyurethane or other plastics foam, applied to it to seal against plate 4 while permitting the plate to be forced into the box to break strip 5. Clearly the lip would need another recess opposite recess 21 for the strip 5.

In another embodiment the switch contacts are of "sealed" construction or together enclosed in an envelope of a flexible plastics film such as polyethylene. The flexibility of the film permits rib 41 to control the switch contacts while the envelope protects the contacts from dirt etc.

The actuator can have forms other than that shown. For-example rib 41- may be reduced with a circular boss which extends through a circular hole in wall 2 and has a projection to operate switch 3. The breakable element, which may be a rod or strip or tube as in the other embodiments, passes through the boss and is also retained in the box 1 as described above. The element may be broken by pulling or pushing plate 4 or by turning it.

If it is desired to keep the plate 4 close to the box after breakage of element 5 rib 41 can be provided with lugs or horns 44 which engage with a slot 14 in the side walls of box 1 so that on the breakage of element 5 plate 4 is constrained to move outwardly and downwardly of the box the lugs or horns moving in the slot. The plate 4 is thus kept with the box in a distinct manner when the element 5 is broken.

The rib 41, or the boss, can have one or more protrusions or recesses to engage with wall 2 or projections therefrom to limit the movement of plate 4 into and/or out of the box.

The breakable element 5 may be horizontal or vertical when the alarm switch assembly is installed, suitable means being provided to prevent the element falling out. The fit of the element is not critical either in length or thickness. The element may be of any suitable crosssection, eg circular, retangular or triangular, and hollow, eg a tube if desired. Although a single element passing through the plate 4 has been described there could be two breakable elements retaining the plate and breakable by forcing a part of the plate 4 between them to flex at least one of them to breaking point to remove the restraint.

The alarm switches embodying the invention and described above are simple to construct and assemble as well as providing an alarm switch with a breakable element which is not likely to injure a person operating the alarm or jam the operation of the alarm.

Figure 3 shows a plan and Figures 4 and 5 respective sectional elevations at IV-IV and V-V of Figure 3 of another alarm switch embodying the invention The alarm switch has a housing portion 100 and an actuator 101.

Both are preferably plastics mouldings, which may be of different colours, or transparent.

The housing 100 may be mounted on a standard electrical wiring accessory box 102 and if required a moulded plastics surround 103 provided for "surface" mounting.

Housing portion 100 and actuator 101 are arranged to hinge together along axis 104 eg by a "dimple-and-hole" moulding form so that the two items can be assembled by being "snapped" together. Actuator 101 has two projections 105, 106 on its inner surface and housing 100 has respectively a recess 107 and an aperture 108 positioned for cooperation with the projections. Projection 106 extends when the alarm switch is assembled ready for use as shown, through aperture 108 to engage the operator 109 of a micro switch 110 mounted on housing 100 and maintain the switch 110 out of a first condition which is the alarm condition. When the alarm switch is used to give an alarm actuator 101 swings away from housing 100, as described below, and projection 106 no longer maintains switch 110 out of the alarm condition so an alarm signal is given over conductors connected to appropriate terminals of switch, 110 as is wellknown.

Projection 105 has a hole 111 which can be aligned with hole 112 and abutments 113,114 in the housing 100, as shown in Figure 4. A breakable element 115 such as a glass rod or tube or the like described above, is placed in the aligned holes and abutments, as shown in Figure 4, to hold the actuator 101 in place in the housing 100. If desired a spring 116 may be housed in recess 107 to act on projection 105, or elsewhere on actuator 101 if preferred.

To operate the alarm switch to give an alarm actuator 101 is moved, eg by pushing it into the frontal recess 117 of the housing, to break breakable element 115. The hold on actuator 101 is thus released and the actuator can now move further, out of recess 117, to take projection 106 out of engagement with operator 109 of micro-switch 110, as described above, and so give an alarm signal. Preferably spring 116 assists in the further movement. Clearly a handle could be provided on actuator 101 and the movement and further movement could be in one direction by pulling the handle to break the breakable element and disengage the actuator from the switch.

To reset the alarm switch the broken breakable element parts are removed and a fresh element installed as described above.

As discussed with reference to Figures 1 and 2 above other forms of alarm construction in accordance with the invention are possible.

If it is desired that parts of the breakable element are not released when the switch is used the actuator may surround the housing and have only a limited further movement. In such an arrangement the alarm switch could be removed as a unit, once used, and replaced with a fresh unit. For example the actuator could extend beyond hole 112 outside the housing and be provided with a hole, not shown, via which the breakable element is inserted. The alarm switch is secured to the mounting by fastening visible only when the breakable element is broken or absent, eg under the extended actuator. The connections to the switch 110 could be push-fit connectors.

Installation is then very simple viz, making the connections, securing the housing and inserting the breakable element. Once used the fastenings are again visible and the unit may be removed and replaced by a fresh one, the broken breakable element remaining inside. The limited further movement of the actuator prevents broken parts escaping. Such an alarm switch is particulary useful for food-handling areas.

The operation of the alarm switch is made visible by the actuator having swung partly or wholly away from the housing.

WHAT WE CLAIM IS: 1. An alarm call point comprising a housing,

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. above. The element may be broken by pulling or pushing plate 4 or by turning it. If it is desired to keep the plate 4 close to the box after breakage of element 5 rib 41 can be provided with lugs or horns 44 which engage with a slot 14 in the side walls of box 1 so that on the breakage of element 5 plate 4 is constrained to move outwardly and downwardly of the box the lugs or horns moving in the slot. The plate 4 is thus kept with the box in a distinct manner when the element 5 is broken. The rib 41, or the boss, can have one or more protrusions or recesses to engage with wall 2 or projections therefrom to limit the movement of plate 4 into and/or out of the box. The breakable element 5 may be horizontal or vertical when the alarm switch assembly is installed, suitable means being provided to prevent the element falling out. The fit of the element is not critical either in length or thickness. The element may be of any suitable crosssection, eg circular, retangular or triangular, and hollow, eg a tube if desired. Although a single element passing through the plate 4 has been described there could be two breakable elements retaining the plate and breakable by forcing a part of the plate 4 between them to flex at least one of them to breaking point to remove the restraint. The alarm switches embodying the invention and described above are simple to construct and assemble as well as providing an alarm switch with a breakable element which is not likely to injure a person operating the alarm or jam the operation of the alarm. Figure 3 shows a plan and Figures 4 and 5 respective sectional elevations at IV-IV and V-V of Figure 3 of another alarm switch embodying the invention The alarm switch has a housing portion 100 and an actuator 101. Both are preferably plastics mouldings, which may be of different colours, or transparent. The housing 100 may be mounted on a standard electrical wiring accessory box 102 and if required a moulded plastics surround 103 provided for "surface" mounting. Housing portion 100 and actuator 101 are arranged to hinge together along axis 104 eg by a "dimple-and-hole" moulding form so that the two items can be assembled by being "snapped" together. Actuator 101 has two projections 105, 106 on its inner surface and housing 100 has respectively a recess 107 and an aperture 108 positioned for cooperation with the projections. Projection 106 extends when the alarm switch is assembled ready for use as shown, through aperture 108 to engage the operator 109 of a micro switch 110 mounted on housing 100 and maintain the switch 110 out of a first condition which is the alarm condition. When the alarm switch is used to give an alarm actuator 101 swings away from housing 100, as described below, and projection 106 no longer maintains switch 110 out of the alarm condition so an alarm signal is given over conductors connected to appropriate terminals of switch, 110 as is wellknown. Projection 105 has a hole 111 which can be aligned with hole 112 and abutments 113,114 in the housing 100, as shown in Figure 4. A breakable element 115 such as a glass rod or tube or the like described above, is placed in the aligned holes and abutments, as shown in Figure 4, to hold the actuator 101 in place in the housing 100. If desired a spring 116 may be housed in recess 107 to act on projection 105, or elsewhere on actuator 101 if preferred. To operate the alarm switch to give an alarm actuator 101 is moved, eg by pushing it into the frontal recess 117 of the housing, to break breakable element 115. The hold on actuator 101 is thus released and the actuator can now move further, out of recess 117, to take projection 106 out of engagement with operator 109 of micro-switch 110, as described above, and so give an alarm signal. Preferably spring 116 assists in the further movement. Clearly a handle could be provided on actuator 101 and the movement and further movement could be in one direction by pulling the handle to break the breakable element and disengage the actuator from the switch. To reset the alarm switch the broken breakable element parts are removed and a fresh element installed as described above. As discussed with reference to Figures 1 and 2 above other forms of alarm construction in accordance with the invention are possible. If it is desired that parts of the breakable element are not released when the switch is used the actuator may surround the housing and have only a limited further movement. In such an arrangement the alarm switch could be removed as a unit, once used, and replaced with a fresh unit. For example the actuator could extend beyond hole 112 outside the housing and be provided with a hole, not shown, via which the breakable element is inserted. The alarm switch is secured to the mounting by fastening visible only when the breakable element is broken or absent, eg under the extended actuator. The connections to the switch 110 could be push-fit connectors. Installation is then very simple viz, making the connections, securing the housing and inserting the breakable element. Once used the fastenings are again visible and the unit may be removed and replaced by a fresh one, the broken breakable element remaining inside. The limited further movement of the actuator prevents broken parts escaping. Such an alarm switch is particulary useful for food-handling areas. The operation of the alarm switch is made visible by the actuator having swung partly or wholly away from the housing. WHAT WE CLAIM IS:

1. An alarm call point comprising a housing,

a switch arrangement having an alarm condition mounted to the housing, an actuator movable with respect to the housing, resilient means for biassing the actuator, and a breakable element engaging the housing and capable of holding the actuator against the action of said biassing means so that the actuator engages the switch arrangement and prevents it from assuming the alarm condition, wherein said actuator substantially encloses the element within the housing and breakage of the element caused by movement of the actuator allows the switch arrangement to assume the alarm condition.

2. An alarm call point according to Claim 1 wherein said element is a solid or hollow elongate body of glass or a plastics material.

3. An alarm call point according to Claims 1 or 2 wherein said element is supported between a slot in the housing and an opposed recess in the housing or in a wall member attached thereto and is capable of engaging a corresponding slot in the actuator.

4. An alarm call point according to Claims 1 to 3 wherein there are two elements.

5. An alarm call point according to Claims 1 to 4 wherein the actuator is pivotally mounted to the housing.

6. An alarm call point according to Claims 1 to 5 wherein the resilient biassing means is a coil spring housed in a recess in the housing and engaging a projection to the actuator.

7. An alarm call point according to Claims 1 to 6 wherein the said resilient biassing means urges the actuator away from the housing.

8. An alarm call point according to Claims 1 to 7 wherein the actuator is a plate forming an outer face of the housing.

9. An alarm call point according to Claims 1 to 8 wherein the actuator comprises a transparent portion through which the inside of the housing is visible.

10. An alarm call point according to any iireceding claim wherein the housing and actuator are comprised of plastics mouldings.

11. An alarm call-point substantially as herein described with reference to the drawings accompanying the Provisional Specification.

12. An alarm call-point substantially as herein described with reference to the accompanying drawings.