GB2255232A

GB2255232A - Alarm call points

Info

Publication number: GB2255232A
Application number: GB9108702A
Authority: GB
Inventors: Stephen John Bayley
Original assignee: Thorn EMI PLC
Current assignee: Thorn EMI PLC
Priority date: 1991-04-23
Filing date: 1991-04-23
Publication date: 1992-10-28
Also published as: EP0510917A2; EP0510917A3; GB9108702D0

Description

-I- SWITCHING--DEVICES 225 52 -332 The present invention relates to

switching devices and in particular to alarm switches commonly known as call points.

A call point is a switch used to activate an alarm by operation of an operating element by a user. Known call points include a frangible window, usually of glass, which is broken in order to change manually to an alarm condition and remain in that condition. The frangible element must provide protection against unintentional operation and deterrent against misuse. Also, to comply with fire regulations, the frangible element, after operation of the call point to signal an alarm, must remain broken or appear to be broken until the call point is reset. However# for glass windows which are broken to activate the alarm, the window must be replaced after each activation. Furthermore, a microswitch is usually incorporated into the call point as the actual switching device, which adds significantly to the manufacturing cost of the call points.

A call point has been proposed which enables operation of the switching element whilst obviating the need to replace the frangible window after each operation, as described in US Patent 4857679. In the arrangement described in US 4857679 the frangible element has a number of frangible areas spaced in succession, one of which is broken off the frangible element each time the device in operated. In the example described, four frangible areas are provided so the frangible element must be replaced after every four operations of the call point. Furthermore, the frangible element is used to operate a separate switching element, with the attendant relatively high cost of providing the separate switching element within the device.

GB 2075265A describes a solid state call point which, as with previous designs, incorporates a frangible glass element, but the element is provided with an electrically conductive path. Resilient contact arms co-operate with the electrically conductive path and a solid state detector to energise an alarm upon activation of the device by breakage of the frangible glass element. To test the call point, one of the.resilient arms can : 2:

be moved away from the conductive path without requiring opening of the device or breaking the glass frangible element. However, such an arrangement is not considered satisfactory as the call point is tested without actual operation of the frangible element which is used to activate the device in a genuine emergency situation. Furthermore, when the device is operated in an emergency situation, the frangible element must be replaced to recommision the call point.

It is an object of the present invention to provide an improved call point which enables activation of the device by displacement of a window element without actually breaking the window element, which provides a tactile feel upon operation, provides a permanent indication of device activation (until reset) and which obviates the need for a relatively expensive switching element within the call point.

Accordingly, there is provided an alarm call point comprising a housing member, a pivotally mounted window member, including a conductive track, being displaceable from a first position with the conductive track In electrial contact with resilient contact means to a further position with the conductive track electrically isolated from the resilient contact means for activation of the call point, and resilient means arranged to co-operate with the window member to releasably retain the window member in the first position.

Preferably, the housing member includes an aperture for receiving a key member having a ramped end portion for engaging the window member for resetting the window member to the first position with the conductive track in electrical contact with the contact means.

The housing member may comprise a cover portion and a chassis portion, each including mutually co-operating projections having arcuate shape end portions, the window member including a recess portion having a cylindrical member extending thereacross, the cylindrical member being arranged to co-operate with the acruate shape end portions for providing a pivotal mount for the window member.

The resilient means to releasably retain the window member in the first position may comprise a resilient arm having an end portion including a ramped surface for engaging the window member in the first position.

The resilient means to releasably retain the window member in the first position may comprise the resilient contact means acting alone or in combination with the resilient arm having the ramped end portion for engaging the window member.

Advantageously, the conductive track is located on a front surface of the window member and the resilient contact means include an extension portion, extending between the housing member and the window member, for providing the electrical contact with the conductive track in the first position.

The present invention will now be described, by way of example only, with reference to the accompanying drawings in which:Figure I is a schematic front view of a call point in accordance with the present invention; Figure 2 is a schematic cross sectional view of the call point shown in Figure 1; Figure 3 is a schematic cross sectional view of a call point incorporating a resilient member for providing a factile response to the operation of the call point; Figure 4 is a schematic cross sectional view showing the resilient member illustrated in Figure 3 in greater detail; Figure 5 is a schematic cross sectional view of a call point according to the present invention and showing the pivotal mounting of the callpoint window; Figure 6 is a schematic view of a window for use in the call point shown in Figure 5; and Figure 7 is a partial schematic side view showing the call point electrical contact in made and broken conditions.

Referring to Figure 1, a call point 2 comprises a housing 4, which may be of moulded plastics material. The housing 4 is, typically, mounted to a wall within easy access to personnel wishing to raise an alarm in an emergency situation, such as a : 4:

fire. The call point is a manually operated device and a window 6 is provided which is activated by applying pressure or striking an indicated position on the window 6, the position usually being indicated by suitable indicia such an arrows 8.

The window 6 is provided with a conductive track 10 on the front surface and near to one edge, which forms a contact member for raising an alarm on activation of the device. The conductive track may be formed by any suitable conductor, such as a conductive ink, a hot foil stamped strip or a copper track. In Figure 2 the window 6 is shown in a first or unoperated position held by resilient contact members 12 which, typically, may be formed from nickel plated spring steel. The contact members 12 include extension portions 14 which extend around the edge of the window 6 into electrical contact with the conductive track 10. The contact members 12 also include knee portions 16 which apply a forward pressure to the window 12, causing the window to engage positively against return portions provided on the housing 4. The resilient contact members serve, therefore, two purposes. Firstly, their shape and resilient nature ensures that a positive tactile feel is provided to the window member for operation of the device, thereby minimising inadvertent operation of the device by accidental pressure applied to the window. Secondly, the contact members 12, in conjunction with the conductive track 10, form the switching device within the call point which, when the electrical contact between the contact members and conductive track is broken, in used to activate the alarm.

A further requirement of the call point, to meet operational regulations, is to ensure that the glass window provides a clear indication, until reset, that the call point has been activated to raise the alarm. As can be seen from Figure 5, a chassis member 18 is provided as part of the housing 4. The housing 4 and chassis 18 are provided, respectively, with projections 20,22 which have arcuate (preferably semicircular) shaped ends which are mutually co-operating. The window 6 is provided with recesses 24,26, as shown in Figure 6, i r, which have cylindrical members 28,30 extending across the recesses. The cylindrical members 28,30 locate within the shaped ends of the projections 20,22 to provide pivot mounts for the window 6 within the housing 4. The window 6 may be fabricated as a transparent plastics moulding as, by the provision of the pivotal mount, and the tactile response provided by the resilient contact members, there is no requirement to actually break the window 6 to operate the call point and raise an alarm.

The tactile response provided to the window 6 may equally be provided by, or enhanced by, a resilient arm 32, such as of plastics material, arranged within the housing 4.

The resilient arm 32 includes an upstanding end portion 34 having a ramp faced end 36 which engages a ramped edge 38 provided on the window 6. As will be seen from Figure 4, the resilience in the arm 32 can be arranged to bias the end 36 into engagement with the ramped edge 38, causing the window to be retained in contact with the return portions on the housing 4.

When the device is activated, the window 6 pivots about the cylindrical members 28,30, thus being displaced from the first or unoperated positions as shown in solid lines in Figure 2, to an active or operated position, as shown in dotted lines in Figure 2. This pivotal movement of the window 6 causes the electrical contact between resilient contact members 12 and the conductive track 10 to be broken, raising the alarm. As the window 6 is displaced from the unoperated position an edge thereof will engage against the knee portion 16 of the contact members 12, flexing the contact members against the natural bias in the contact members, thereby to provide the tactile response to the window 6. Similarly, if the resilient arms 32 are provided in addition or as an alternative to the resilient contact members, the movement of the window 6 in the direction of arrow A from the unoperated position will cause the end portion 34 of the resilient arm 32 to flex in the direction of arrow B, as shown in Figure 4, as the end 38 of the window 6 ramps over the end face 36 of end portion 34.

: 6:

When the window 6 disengages the knee portions 16 of resilient contact members 12, as shown in dotted lines in Figure 7, the window is retained within a restricted area defined by the knee portions 16 and return portions 38 provided on the contact members 12. It will be realised that the width of this restricted area may be controlled by defining the length of straight portions 40 of the contact members 12 so that# in the operated condition, the window 6 may be allowed a restricted degree of 'free' pivotal movement to provide an indication that the call point has been activated, or the windows 6 may be held more positively in the operated position. In either arrangement the indication of an alarm having been raised may be enhanced by the provision of a light emitting member, such as an LED, positioned behind a membrane portion provided on the chassis 18.

In a likewise manner, it will be realised that the end portion 34 of the resilient arm 32 way be appropriately dimensioned to positively hold or provide a restricted degree of movement to the window 6 in the operated condition.

It can be seen from Figure 7 that in the operated condition, the conductive track 10 cannot contact the resilient contact members 12 unless the window 6 is positively reset to force the edge of the window back over the knee portion 16.

To enable the call point to be reset without having to dismantle the housing, as is required in current call point designs to replace the broken glass windowe an aperture 42 is provided on the housing 4 to receive a resetting key 44, as shown in Figure 5. The key 44 includes an extension 46 which is provided with a ramped end face 48 which may engage a co-operating face or lug provided on the window to force the window back over the knee portion to reset the call point.

It will be appreciated from the above description that a call point according to the present invention enables the necessary electrical switching to be achieved without the use of a relatively expensive microswitch usually incorporated into the call point. Furthermore, the call point may be tested by actual operation rather than by a simulation technique of moving a glass window away from a microswitch. Additionally, once operated, either for testing or by raising an actual alarm, the call point may be easily and readily reset by operation of the key device without having to open the call point housing.

Although the present invention has been described with respect to specific embodiments, it will be realised that modiciation may be effected whilst remaining within the scope of the invention. For example, other pivot arrangements may be used to mount the window member. Additionally, other materials may be used to provide the resilient contact members, such as resilient plastic arms with appropriate electrically conductive tips and tracks to provide the switching path to the conductive track 10 on the window 6.

1

Claims

CIAIMS

1. An alarm call point comprising a housing member, a pivotally mounted window member, including a conductive track, being displaceable from a first position with the conductive track in electrical contact with resilient contact means to a further position with the conductive track electrically isolated from the resilient contact means for activation of the call point, and resilient means arranged to co-operate with the window member to releasably retain the window member in the first position.

2. A call point according to claim 1 wherein the housing member includes an aperture for receiving a key member having a ramped end portion for engaging the window member for resetting the window member to the first position with the conductive track in electrical contact with the contact means.

3. A call point according to claim 1 or claim 2 wherein the housing member comprises a cover portion and a chassis portion, each including mutually co-operating projections having arcuate shape end portions, the window member including a recess portion having a cylindrical member extending thereacross, the cylindrical member being arranged to co-operate with the arcuate shape end portions for providing a pivotal mount for the window member.

4. A call point according to claim 3 wherein the chassis portion includes a membrane portion, and the call point includes a light emitting member for indicating an alarm condition through the membrane portion when the window member is displaced from the first position.

5. A call point according to any one of the preceding claims wherein the resilient means to releasably retain the window member in the first position comprises a resilient arm having an end portion including a ramped surface for engaging the window member in the first position.

6. A call point according to any one of the preceding claims wherein the resilient means to releasably retain the window member X 9:

in the first position comprises the resilient contact means.

7. A call point according to any one of the prededing claims wherein the conductive track is located on a front surface of window member and the resilient contact means include an extension portion, extending between the housing member and the window member, for providing the electrical contact with the conductive track in the first position.

8. A call point according to any one of the preceding claims wherein the window member comprises a moulding of transparent plastics material.

9. A call point according to any one of the preceding claims wherein the resilient contact means comprise nickel plated spring steel.

10. A call point substantially as hereinbefore described with reference to the accompanying drawings.