GB2298963A - Switch assembly - Google Patents

Abstract

A switch assembly comprises a housing defined by first and second housing members each defining a substantially planar base wall 52, 90 with the second housing member being mounted within the first housing member in a hermetically sealed relation therewith to define a chamber between parallel base walls 52, 90, a plurality of depending electrically conductive tubes 28, 30, 32 fixed to the housing second member base wall 90 in hermetically sealed relation thereto.

Description

HERMETICALLY SEALED SNAP SWITCH ARRANGEMENT This invention relates to switch assemblies that are intended to be installed as part of a complete control for fluid and bulk solid flow or storage systems, and more particularly, to arranging such assemblies for complete hermetic sealing so as to prevent the passage of gas or electrical arcs from within the switch assembly to the exterior of the switch assembly, and to enhance the performance of such a switch assembly as a control in explosive, corrosive, dusty, and damp environments.

Control switch assemblies are commonly used in complete control systems for fluid flow and bulk solid material flow or storage systems that may indicate such important factors as pressure, fluid flow, fluid level, bulk solid material levels, proximity valve positions, etc. However, a major problem with equipment of this type is that it is not hermetically sealed even though some sealing may be involved.

in accordance with the present invention there is provided a hermetically sealed assembly comprising: a housing defined by first and second housing members, said housing members each defining a substantially planar base wall, said first housing member being formed from imperforate material, said second housing member being mounted within said first housing member in hermetically sealed relation therewith, and with said base walls of said housing members being disposed in substantial parallelism to form said housing and define a chamber between said base walls of said housing members, said housing second member base wall including a plurality of depending electrically conductive tubes fixed to same in hermetically sealed relation therewith, said housing second member otherwise being formed from imperforate material, said tubes each being disposed relative to said housing such that one end of each of said tubes projects away from said chamber, said base wall of said first housing member having a portion of same indented out of the plane thereof to form a hermetic wall portion, a first lever disposed externally of said housing, said first lever extending in general parallelism to said base walls and being fixed to said hermetic wall portion a switch arranged at the distal of said first lever for actuation by the first lever a second lever disposed internally of said chamber and being fixed to said hermetic wall portion, said tubes provide the option of purging said chamber and backfilling same with a gas through one of said tubes, and an electrical insulating layer adjacent said second housing member base wall.

The present invention provides a switch assembly of the general type indicated that includes a housing which is fully hermetically sealed to prevent the passage of gases or electrical arcs from within the chamber.

Further, the housing arrangement for the switch assembly can be arranged to accept a subminiature snap action switch of the conventional types that is provided with projecting pin type terminals by providing the housing switch mounting structure with depending tubes that are hermetically sealed and positioned to slidingly receive the respective pin type terminals of the switch so that the respective depending tubes may be hermetically sealed closed relative to the switch terminal received within same, and lead wire connections made to the respective tubes which connections are in turn hermetically sealed by being covered with a potting material.

In the preferred embodiment the hermetically sealed housing defines a dimple or indentation to which external and internal lever arms are fixed appropriately actuating the switch when a predetennined force acts on the switch assembly. The internal lever is within the hermetically sealed chamber defined by the housing involved.

Also provided in accordance with this invention is a method of hermetically sealing a chamber in a switch assembly that includes a housing defined by first and second housing members each defining a substantially planar base wall, said first housing member being formed from imperforate material, said housing second member being mounted within said first housing member in hermetically sealed relation therewith, and with said base walls of said housing members being in substantial parallelism to form said housing and define a sealed chamber between said housing member base walls, a switch mounted externally of the chamber, said housing second member base wall including a plurality of open ended depending tubes affixed to same and projecting therefrom in hermetically sealed relation therebetween, and said second housing member otherwise being formed from imperforate material, including the steps of: hermetically sealing the depending ends of all but one of said tubes, applying one end of a flexible conduit in sealed relation to the depending end of said one tube, purging said housing chamber through said conduit, backfilling the said housing chamber with a gas, removing said conduit one end from said one tube, hermetically sealing the depending end of said one tube, and covering the projecting portions of all said tubes with a potting material.

Preferably the potting material is a two part epoxy resin.

A full understanding of the invention will become apparent from a consideration of the following detailed description with reference to the accompanying drawings in which: Figure 1 is side elevation view of a fully hermetically sealed snap switch assembly in accordance with the present invention, from the lower end of which projects the usual lead wires that extend to the electrical components to be controlled by the switch assembly ofFigure 1; Figure 2 is a side elevational view of the far side of the switch assembly as shown in Figure 1; Figure 3 is a bottom plan view of the switch assembly shown in Figures 1 and 2; Figure 4 is a top plan view of the switch assembly shown in Figures 1 through 3; Figure 5 is a sectional view, through the switch assembly, shown along lines 5--5 of Figure 4, with the potting material shown in Figure 3 omitted;; Figure 6 is a view similar to Figure 5, but with such potting material included; and Figure 7 is a larger scale view of Figure 6.

However, it is to be distinctly understood that the drawing illustrations referred to are provided primarily to comply with the disclosure requirements of the Patent Laws, and that the invention is susceptible of modifications and variations that will be obvious to those skilled in the art, and that are intended to be covered by the appended claims.

The present invention provides a hermetically sealed snap switch arrangement 10 that is to be used as part of a complete control system, as indicated, for indicating, for instance, pressure, fluid flow and/or level, bulk solid level, proximity, valve position, etc.

While the hermetically sealed switch arrangement 10 is of wide applicability in connection with such control systems, the incorporation of the hermetically sealed snap switch arrangement 10 in control systems used in explosive, corrosive, dusty, and damp environments, enhances the performance of such controls.

Referring now more specifically to the drawings, reference numeral 10 generally indicates the hermetically sealed switch arrangement of the present invention, which comprises hermetically sealed housing 11 defined by outer housing member 12 and inner housing member 14, with the housing members 12 and 14 defining hermetically sealed switch chamber 16 in which a conventional snap switch 18 provided with an actuating member 20 (see Figures 5-7) is operably mounted, without requiring the usual mounting bracket for the switch 18.

The Applicant's hermetically sealed snap switch arrangement 10 that is illustrated in the drawings represents a preferred embodiment of the invention, although it will be apparent that some features of the preferred embodiment that are hereinafter disclosed may be varied at the option of those skilled in the art.

In accordance with the Applicant's invention, the switch 18 is of the type having projecting pin type terminals 22,24,26 (see Figures 5-7) that are available in conventional snap switches of this general type that are offered by a number of US companies, such as the Micro-Switch Division of Honeywell, Inc., Freeport, Illinois.

Hermetically sealed mounted in inner housing member 14 and disposed to project outwardly of switch chamber 16 are a similar number of open ended tubes 28,30 and 32 that are oriented and proportioned for slip fit receiving, respectively, the respective pin type terminals 22,24,25 of the switch 18, and mounting the switch 18 within the chamber 16, in the manner indicated in Figures 5-7, free of any mounting bracket.Further, the housing members 12 and 14 are connected together in such a manner that the chamber 16 is hermetically sealed thereabouts at their abutting portions indicated in Figures 5-7, with the switch actuating member 20 being activated by an external layer 34 that actuates internal lever 36 through a housing hermetic wall portion 38 (see Figures 5-7) to which both levers 34 and 36 are suitably bonded or fixed; the respective switch terminals 22,24 and 26 are respectively hermetically sealed with respect to the respective housing tubes 28, 30 and 32 (in which they are respectively mounted), and lead wires 40,42, and 44 are electrically connected, in a hermetically sealed fashion, to the respective housing tubes 28, 30, and 32, with the remaining space that is defined by the housing 11 exterior of inner housing member 14 being filled with a suitable potting material 48 that overlies the electrical connections of the respective lead wires 40,42, and 44 to the respective tubes 28, 30, and 32, and thus hermetically seals such connections.

The outer housing member 12 comprises a cover 50 that is of rectangular dished or cupped shape configuration that is suitably formed from a suitable grade of steel in imperforate sheet metal form to define base wall 52 that is integral with encompassing side wall 54 that extends from the base wall 52 to the side wall marginal rim portion 56 that is encompassing relation with respect to the housing 11. The base wall 52 of the outer housing member 12 is essentially planar in configuration, except where it is formed to define the indentation or dimple 58, which defines the housing hermetic wall portion 38 that essentially parallels the outer housing member base portion 52, and that is circumscribed by annular base wall segment 59.

Associated with the outer housing member 12 is external lever 34 that at its distal end 60 has suitably affixed thereto a contact 62 (see Figures 5-7) which is spot welded or otherwise suitably affixed to the exterior of outer housing member hermetic wall portion 38, with the lever 34 also defining proximal end 64 that, in accordance with the present invention, effects activation of switch 18. For this purpose, inner lever 36 is provided having distal end 66 integral with contact 68 that is also suitably fixed to the interior of the hermetic wall portion 38 of the outer housing member 12; the proximal end 70 of the internal lever 36 operably engages the actuating member 20 of the switch 18 (see Figures 5-7).

Levers 34 to 36 are suitably formed from strips of relatively stiff metallic material, since their function is to transmit without substantial deflection downward thrust that is applied to the proximal end 64 of external lever 34 to physically move the proximal end 70 of the internal lever 36, by way of both levers 34 and 36 being affixed to the hermetic wall portion 38 of housing member 12 that flexes independently of base wall 52 for this purpose, whereby the internal lever 36 is activated to depress switch actuation member 20 and thereby actuate the switch 18 in accordance with the specific arrangement of this snap switch and the manner in which the installer has installed assembly 10 in the control system of which the assembly 10 is made a part. For this purpose, levers 34 and 36 are preferably disposed in substantial parallelism.

The switch 18 may be in the form of any suitable conventional subminiature snap action switch of the type indicated, which is provided with conventional pin type terminals 22, 24, and 26.

The outer housing member 12 also includes a pair of spaced mounting tubes 72 and 74 (see Figures 5 - 7) that are open ended, extend transversely or crosswise of the housing member 12, and have their respective ends (73, 75, 77, and 79) welded to and about corresponding apertures 78, 80, 82, and 84 that are formed in the side wall 54 of the outer housing member 12 in any suitable manner to effect a hermetic seal at these corresponding locations of the assembly 10.The cross tubes 72 and 74 are for the purpose of suitably mounting the hermetically sealed snap switch arrangement 10 by passing suitable mounting screws (not shown) through the open bores of these tubes and fixed structure apaturing that suitably mounts assembly 10 for operation purposes when it is installed (it is assumed, of course, that suitable nuts or the like are applied to such screws to hold the assembly 10 involved in place).

The inner housing member 14 is also a rectangular dished or cupped configuration and is proportioned to fictionally slip inside the marginal rim portion 56 defined by the outer housing member 12. The inner housing member 14 defines base wall 90 (see Figures 5-7) that is integral with side wall 92 thereabout, which extends between the indicated base wall 90 and the marginal rim 94 of the inner housing member side wall 92. The base wall 90 of the inner housing member is formed with a number of eyelets 96 (see Figure 7) in spaced apart relation that are numerically the same as the number of pin type terminals that the switch 18 is to have, with the respective tubes 28, 30, and 32 being hermetically sealed to such eyelets 96 respectively, with glass seals 95, 97, and 99 (see Figure 7, that may be formed of any suitable type of glass material that is arranged for hermetic sealing purposes); the respective tubes 28, 30, and 32 are located relative to the inner housing member 14 to smoothly accept the respective switch terminals 22, 24, and 26 respectively; a suitable layer or sheet of insulating material 100 preferably separates switch 18 from the inner housing member base wall 90, which layer 100 may be formed from commercially available RTV rubber; it is, of course, preferable that the layer 100 be apertured in accordance with the orientation of the respective switch terminals 22, 24, and 26 since such switch terminals extend from the switch 18 well into the respective tubes 28. 30, and 32, as indicated in Figures 5-7. Further, the externally disposed ends 101 ofthe respective terminals 22, 24, and 26 are respectively soldered to and about the respective tubes 28, 30, and 32, that they are received in (as at 103) to hermetically seal the respective tubes 28, 30, and 32.

For purposes of 'wiring' switch 18, the respective lead wires 40, 42, and 44 each comprise the usual metallic, electrically conducting, core 102 within the usual insulative covering 104; in accordance with the present invention, the cores 102 of the respective lead wires 40, 42 and 44 are operably connected to the respective switch pin type terminals 22, 24, and 26 by being connected to their respective tubes 28, 30, and 32 in some manner.As shown in Figures 5 through 7, this may be done by wrapping the respective lead wire cores 102 around the respective tubes 28, 30 and 32 and spot welding or soldering them in place (as at 105), or by employing a suitable conventional mechanical device for connecting the respective lead wire cores to the respective tubes, which may be of the so-called 'quick connect' or 'stake-on' type, for instance.The remaining volulnes of the space surrounding the electrical connections to the lead wires 40, 42 and 44 to the respective tubes 28, 30, and 32 is filled with a suitable potting compound 48 which preferably overlies the electrical connections of the respective lead wires 40, 42, and 44 to the respective tubes 28, 30, and 32, and the hermetic sealing 103 of the respective tubes 28, 30 and 32 to the respective switch terminals, down to and including the terminal portions of the respective lead wire covers 104. A potting material preferred for this purpose is the EL CAST Resin 4123 hardener that is available from United Resin Corporation, of Santa Ana, California.

As indicated, the inner housing member 14 is proportioned for slip fit application within the side wall 54 of the outer housing member 12, as indicated in Figures 5 through 7, and with the switch 18 and lead wires 40, 42, and 44, applied to the ilmer housing member 14 as indicated, the inner housing member 14 is slipped within the rim 56 of side wall 54 of the outer housing member, and the joint between the inner housing members 12 and 14 is suitably hermetically sealed, as by welding same continuously about the margin 56 (prior to the application of the potting material 48 to the inner housing member 14) or in any other suitable manner.

The resulting hermetically sealed snap switch arrangement 10 is adapted for retrofitting into controls which utilize the Basic Series Switch (which is an industry standard).

When a suitable sensing mechanism through a suitable transmitter means (not shown) deflects the proximal end 64 of the external lever 34 of Figures I through 7 of the drawings, counter clockwise of Figures 5-7, lever 34 moves as a whole in the same direction, with its contact 62 at its distal end 60 similarly flexing hermetic wall portion 38 in the same direction, thereby effecting movement of the internal lever 36 as a whole in the same direction.

Since the contact 68 at the distal end of lever 36 is affixed to hermetic wall portion 38, movement of internal lever 36 is in the same direction as that experienced by extemal lever 34, whereby internal lever 36 actuates switch 18 in accordance with the options worked into the control system by the installer.

The biasing action of the switch 18 on its actuator 20 effects repositioning of the levers 36 and 34 to their original positions of drawing Figures 1-7.

It will be apparent to those skilled in the art that the hermetically sealed switch arrangement 10 also works in a reverse manner so as to actuate a suitable switch (not shown) with which external lever 34, and specifically its proximal end 64, is associated, provided, of course, that the conventional switch that is used for this purpose (in place of switch 18) is suitably arranged to this end.

The present invention also contemplates that after assembly in the manner indicated, the switch chamber 16 may be purged and then backfilled with a gas, such as hydrogen, nitrogen, or helium, to enhance the electrical life of the subminiature snap switch 18 employed in connection with this invention.For this purpose, one ofthe tubes 28, 30, or 32 is initially left free of hermetic sealing 103 with respect to the switch terminal received therein, and before the potting material 48 is applied to the assembly 10, one end of a suitable flexible conduit (not shown) is applied to the exteriorly projecting end of the unsealed tube, and a suitable reversible gas pump or the like is applied to the other end of the conduit to first purge the chamber 16 of air and other gas remaining in same, and then reversing the pump involved, supplying a gas (such as the aforementioned hydrogen, nitrogen, or helium) to the chamber 16 as desired. Thereafter, the indicated flexible conduit is removed from the indicated tube of the assembly 10, after which such tube of assembly 10 is hermetically sealed with respect to the switch terminal received therein, after which the potting material 48 is applied to complete the device 10 as indicated.

A major improvement provided by the present invention is the hermetic sealing of the assembly tubes 28, 30, and 32 by applying the glass sealing arrangement thereto that is described and illustrated. Another important improvement is the presence of the tubes 28, 30, and 32 themselves, which, as a whole, act as a socket that accepts the pin type terminals of subminiature snap action switches such as a switch 18. Further, the mounting arrangement for the subminiature snap action switch 18 eliminates the need for mounting brackets for same.

The foregoing description and the drawings are given merely to explaining and illustrate the invention, and the invention is not to be limited thereto, except insofar as the appended claims are so limited, since those skilled in the art who have this disclosure before them will be able to make modifications and variations therein without departing from the scope of the invention.

The hermetically sealed snap switch assembly described above is described also and claimed in our co-pending British Patent Application No 9305540.8 (Publication No 2267998) from which this application is divided.

Claims (10)

Claims

1. A hermetically sealed assembly comprising: a housing defined by first and second housing members, said housing members each defining a substantially planar base wall, said first housing member being formed from imperforate material, said second housing member being mounted within said first housing member in hermetically sealed relation therewith, and with said base walls of said housing members being disposed in substantial parallelism to form said housing and define a chamber between said base walls of said housing members, said housing second member base wall including a plurality of depending electrically conductive tubes fixed to same in hermetically sealed relation therewith, said housing second member otherwise being formed from imperforate material, said tubes each being disposed relative to said housing such that one end of each of said tubes projects away from said chamber, said base wall of said first housing member having a portion of same indented out of the plane thereof to form a hermetic wall portion, a first lever disposed externally of said housing, said first lever extending in general parallelism to said base walls and being fixed to said hermetic wall portion a switch arranged at the distal of said first lever for actuation by the first lever a second lever disposed internally of said chamber and being fixed to said hermetic wall portion, said tubes provide the option of purging said chamber and backfilling same with a gas through one of said tubes, and an electrical insulating layer adjacent said second housing member base wall.

2. A switch assembly as claimed in claim 1, wherein; said first and second housing members are cupped shape in configuration with each of said housing members defining in addition to said base walls a side wall thereabout that extends from the respective member base walls to a marginal rim portion disposed about said housing, with said side wall of said second housing member extending from said base wall thereof a predetermined fraction of the distance that said side wall of said first housing member extends from said base wall thereof, said second housing member being received in said marginal rim portion of said housing member for mounting said second first housing member with said first housing member, within said marginal rim portions of said housing members projecting from the base walls thereof, respectively, in the same direction.

3. A switch assembly as claimed in claim 1 or 2, including: a pair of mounting tubes extending through said chamber and disposed in coplanar relation with a plane that substantially parallels the respective housing member base walls, said mounting tubes extending between opposite portions of said first housing member and being hermetically sealed relation therewith.

4. A switch assembly as claimed in any of claims 1 to 3, wherein: lead wires are electrically connected to the respective tubes, and a potting material overlies both said lead wire connections to the tubes and said ends of said tubes.

5. A switch assembly as claimed in claim 2, wherein: lead wires are electrically connected to the respective tubes, and a potting material overlies said lead wire connections to the tubes substantially fills the space defined by said second housing member base wall and side wall.

6. A switch assembly as claimed in any preceding claim, wherein: said tubes are each disposed in an eyelet formed in said housing second member base wall, with said tubes being respectively fixed to said housing second member base wall by glass seals that form said hermetically sealed relation thereto.

7. A method of hermetically sealing a chamber in a switch assembly that includes a housing defined by first and second housing members each defining a substantially planar base wall, said first housing member being formed from imperforate material, said housing second member being mounted within said first housing member in hermetically sealed relation therewith, and with said base walls of said housing members being in substantial parallelism to form said housing and define a sealed chamber between said housing member base walls, a switch mounted externally of the chamber, said housing second member base wall including a plurality of open ended depending tubes affixed to same and projecting therefrom in hermetically sealed relation therebetween, and said second housing member otherwise being formed from imperforate material, including the steps of: : hermetically sealing the depending ends of all but one of said tubes, applying one end of a flexible conduit in sealed relation to the depending end of said one tube, purging said housing chamber through said conduit, backfilling the said housing chamber with a gas, removing said conduit one end from said one tube, hermetically sealing the depending end of said one tube, and covering the projecting portions of all said tubes with a potting material.

8. The method set forth in claim 7, wherein: the potting material is a two part epoxy resin.

9. A hermetically sealed switch assembly according to claim 1 and substantially as herein described with reference to the accompanying drawings.

10. A method of hermetically sealing a chamber in a switch assembly according to claim 7 and substantially as herein described.