GB2248343A

GB2248343A - Control panels for pressurised enclosures

Info

Publication number: GB2248343A
Application number: GB9120558A
Authority: GB
Inventors: Michael L Firth
Original assignee: Telektron Ltd
Current assignee: Telektron Ltd
Priority date: 1990-09-28
Filing date: 1991-09-27
Publication date: 1992-04-01
Anticipated expiration: 2011-09-27
Also published as: GB9120558D0; GB9021188D0; GB2248343B

Abstract

An enclosure under positive internal pressure has a control panel (6), eg a membrane keyboard, mounted in an opening (2) of the wall (1) of the enclosure. The control panel (6) is protected by an assembly comprising two membranes (14, 18) positioned either side of a panel (10) which is provided with a plurality of holes (11) accommodating button elements (20) for actuating the control panel (6). The inner membrane (18) acts as a main seal for the enclosure. <IMAGE>

Description

Pressurisation Protection System with Keyboard This invention relates to enclosures intended to be maintained under positive internal pressure for reasons of safety, and the invention is concerned in particular with such an enclosure mounting therein a control panel, especially in the form of a membrane keyboard.

In situations where dangerous, e.g.

explosive atmospheres can occur it is common for machinery, such as electrical equipment, to be housed in an enclosure to which inert gas, usually air, is supplied to maintain the interior of the enclosure at a pressure above that of the ambient atmosphere. In some cases the apparatus accommodated in the enclosure requires a means of control during operation whereby an operator can make adjustments to the apparatus and/or its mode of operation. To this end it is known to provide an opening in an enclosure wall and to mount a membrane keyboard within the enclosure to cover and at the same time seal closed the opening to prevent escape of gas from inside the enclosure.A drawback of this arrangement is that the membrane keyboard is exposed and vulnerable to damage by external knocks, and it is required to withstand the internal pressure itself, which is not at all related to its main function as a control panel. If any leakage should occur through or past the membrane keyboard it means inconvenient and costly downtime of the enclosed machinery, and could even lead to a potentially dangerous condition.

The present invention aims to provide a solution to these drawbacks and provides a protection assembly comprising a substantially rigid panel adapted to be mounted on enclosure to span an opening in a wall thereof, and to be sealed to said wall around said opening, an outer membrane for covering the outer surface of the panel, a plurality of button elements accommodated in through holes provided in said panel, and an inner membrane covering the inner surface of panel to seal closed the holes therein with respect to the interior of the enclosure.

With such an assembly the inner membrane provides a pressure seal to retain the pneumatic pressure within the enclosure, and the outer membrane gives protection against damage by external impacts as well as acting to retain the button elements which are preferably separate members although they could be made integral with or be fastened to either of the inner and outer membranes. The panel holes and button elements are arranged to match the configuration of the keyboard control panel which is positioned immediately behind the inner membrane whereby the keys can be actuated by depressing the respective buttons, the membranes exhibiting adequate flexibility to facilitate the degree of movement of the button elements required in this respect.

The invention also resides in an enclosure equipped with a keyboard control panel and including a protection assembly as defined above.

The aforementioned and other preferred features of the invention will be understood better from the following detailed description of an embodiment, given with reference to the accompanying drawings, in which: Figure 1 is a partial plan view of a membrane keyboard installation in accordance with the invention; Figure 2 is a cross-section taken along the line II-II of Figure 1; Figure 3 is a detail view showing the part circled in Figure 2 and illustrating a modification; and Figure 4 is a cross section, similar to Fig 2, through an alternative installation in accordance with the invention.

An enclosure for housing electrical machinery, for instance, has a wall 1 defined by sheet metal. Within this wall is a rectangular opening or window 2, only a corner portion of which is illustrated in the drawings.

In the installation of Figures 1 to 3 mounting studs 3 are fixed, e.g. welded, to the inner surface of the wall 1 and are spaced apart around the periphery of the opening 2. These studs project inwardly and have screw-threaded ends for receiving nuts 4 which secure in place on the wall 1 a membrane keyboard and protection assembly therefor. The membrane keyboard 6 is supported by a rigid backing plate 7 and has a termination 8 extending from an edge thereof. The construction of the membrane keyboard is well known per se and forms no part of the present invention.

The protection assembly includes a rigid button plate 10 conveniently made of metal and having a first set of holes through which the studs 3 pass, and a second set of holes 11 positioned within the area of the opening 2 and arranged to conform with the predetermined array of key areas on the membrane keyboard 6. Covering the outer surface of the button panel 10 is an outer membrane 14 which is imperforate except for holes through which the studs pass. The outer membrane and hence the button panel are sealed to the wall 1 around the entire circumference of the opening 2 by an annular gasket 15. Interposed between the inner surface of the button panel 10 and the membrane keyboard 6 is an inner membrane 18, which like the outer membrane is imperforate except for holes to accept the studs 3.Loosely accommodated in the holes 11 of the button panel between the inner and outer membranes are buttons 20, the lower surfaces of which are convex to concentrate the pressure exerted on the key areas of the membrane keyboard when the buttons are depressed.

The membranes 14, 18 and the buttons 20 can be made from plastic, rubber or metal, but the membranes need to have sufficient flexibility to transfer finger pressure exerted on the outer membrane to the membrane keyboard. Advantageously, the membranes and buttons are made of transparent plastics, which enables characters, e.g. letters and numbers as shown, marked on the keyboard key areas to be viewed from outside the enclosure despite the interposition of the protection assembly. The button panel may be made of metal, but can also be made of clear plastics to further enhance the visibility of the membrane keyboard. If the keyboard is not visible corresponding markings which are visible are preferably applied to a part of the protection assembly, e.g. to the outer faces of the buttons 20, or the outer membrane.Thus, if the outer membrane is of metal, such as stainless steel foil the character markings could be etched on the foil.

In use of the enclosure, the inner membrane acts as the main seal to retain the pneumatic pressure within the enclosure. The outer membrane contains the buttons in the button panel and provides protection against impact damage. In addition the outer membrane provides extra security in the event that the inner membrane should fail. The construction of the protection assembly ensures minimal frictional losses in the transmission of actuating pressure to the membrane keyboard and thereby the tactile feel of the keyboard is substantially retained, which is of considerable benefit regarding ease of operation.

As shown in Figure 1 and 2 the opening 2 and the gasket 15 define a sharp edge whereby corners are formed in which dust may collect. Figure 3 shows a modification in which a fillet or bead 30 of triangular cross-section is inserted to define a bevelled face whereby the sharp corner is eliminated. This modification may be of particular benefit when the keyboard is installed on an inclined wall. The fillet may be a separate element or can be integral with the gasket 15. Figure 4 shows an alternative embodiment essentially as described above in connection with Figs 1 and 2, but in which the membrane protection assembly comprising the button plate 10, the inner and outer membranes 14, 18 and the buttons 20, is mounted on the outer side of the enclosure wall 1 with the inner membrane 18 being sealed to the wall by the annular gasket 15. The studs 3 securing the membrane protection assembly may be threaded into tapped holes in the button plate 10 and pass through holes in the inner membrane, the gasket 15 and the enclosure wall to receive the securing nuts 4 within the enclosure. The backing plate 7 for the membrane keyboard 6 is located in the opening of the enclosure wall and may be supported by additional studs or bolts 23 fitted to the button plate 10 and passing through holes in the backing plate to receive nuts 24. Further support may be provided by clamp bars 25 extending between bolts 23. Alternatively, to obviate the need for the bolts 23, supporting or clamping bars for the backing plate 17 may extend across the enclosure opening between the studs 3. The membrane protection assembly of Fig 4 is otherwise constructed and performs as described in relation to the first embodiment.

Claims

CLAIMS:

1. A protection assembly comprising a substantially rigid panel adapted to be mounted on an enclosure to span an opening in a wall thereof and to be sealed to said wall around said opening, an outer membrane for covering the outer surface of said panel, a plurality of button elements accommodated in through holes provided in said panel, and an inner membrane for covering the inner surface of the panel to seal the holes therein with respect to the interior of the enclosure.

2. A protection assembly as claimed in claim 1 wherein the button elements have convex inner surfaces.

3. A protection assembly as claimed in claim 1 or 2 wherein the button elements are separate from the inner and outer membranes.

4. A protection assembly as claimed in any of claims 1 to 3 wherein the inner and outer membranes are made of a transparent plastics material.

5. A protection assembly as claimed in any of claims 1 to 3, wherein the outer membrane is made of metal foil.

6. A protection assembly as claimed in any preceeding claim wherein an annular gasket is provided for sealing between one of the membranes and the enclosure wall.

7. An enclosure equipped with a keyboard control panel and including a protection assembly as claimed in claim 1, wherein the button elements are positioned to conform with the predetermined array of key areas on the keyboard and the inner membrane acts as a main seal for the enclosure.

8. An enclosure as claimed in claim 7 wherein sealing is provided between the enclosure wall and one of the membranes by means of a gasket.

9. An enclosure as claimed in claim 7 or 8 wherein the outer membrane is within the enclosure and fillet means are located around the edge of the opening to define a bevelled surface between the enclosure wall and the outer membrane.

10. A protection assembly substantially as herein described with reference to the accompanying drawings.

11. An enclosure substantially as herein described with reference to the accompanying drawings.