GB2251517A - Electrical switches - Google Patents

Abstract

An electrical switch is actuated by means of a pressure differential exerted across a diaphragm 10 which is a substantially planar sheet of material supported along its periphery 12 and having in an unsupported central area 13 a series of radial elongate indentations 14 to cause the central portion to adopt a first position and rapidly move to a second position with a predetermined differential across the diaphragm. <IMAGE>

Description

ELECTRIC SWITCHES This invention relates to electric switches in general but more particularly to switches for use in connection with vacuum systems, for example vacuum coating apparatus, to disconnect the relevant parts of the apparatus when not in use.

Many processes can be performed under vacuum and the apparatus in which they are conducted generally supplies high current/voltages to the relevant components during use. When such processes are terminated or when the apparatus is generally not in use, there is clearly a need to ensure that the electrical circuits are broken to allow access to the apparatus by the operator.

In practice, there should be provided (and Governmental restrictions are increasingly making it compulsory) means to break the electrical circuits at a predetermined pressure within the apparatus so that the electric current is off in the region of ambient pressure but is on at the lower working pressures in the vacuum chamber.

Electrical switches are known which are activated by means of contact with a diaphragm itself in contact with the apparatus pressure; generally distortion of the diaphragm with increasing pressure, ie as the apparatus is brought towards ambient pressure after use, activates a switch contact by direct pressure.

However, a problem with such known switches is that the activation of the switch is not sudden and can occur over a range of pressures with the slow movement of the diaphragm. Furthermore, if the increase (or decrease) of pressure occurs relatively slowly, the switch can be turned on and off in quick succession which may lead to arcing in the switch and generally detract from the operation of the apparatus.

Such a slow acting diaphragm can be used with a "snap action" micro-switch; however, these switches are not recommended in safety applications.

The present invention provides an electrical switch for use in particular with vacuum apparatus to disengage electric current within the apparatus at ambient pressures which is more positive and fast acting in operation.

In accordance with the invention, there is provided an electrical switch arrangement which is activated by means of a pressure differential exerted across a diaphragm, wherein the diaphragm is a substantially planar sheet of material supported along its periphery and having in an unsupported central area a series of radially (arrayed) elongate indentations to cause the central portion to adopt a first position and rapidly move to a second position with a predetermined differential across the diaphragm.

The switch arrangement of the invention is particularly useful in conjunction with a positive action (or positive break) switch, ie one in which the switch is closed and capable of passing current when in an unoperated position, and a deliberate cut, for example opening a guard, is necessary positively to depress the switch actuator to reverse this condition and open the circuit. With the invention the snap-acting diaphragm opens the circuit.

Preferably the diaphragm is supported across a passageway or nozzle which is associated with a switch and which is arranged for communication with a pressure or vacuum vessel. In such cases, the pressure of the vessel acts on one side of the diaphragm and ambient pressure acts on the other side of the diaphragm.

Thus, when, for example, the vessel is evacuated, the pressure differential across the diaphragm is increased such that the diaphragm moves from its first position to its second position at the stage when the vacuum in the vessel causes a predetermined pressure difference across the diaphragm; thereby activating the switch and allowing current to flow to apparatus in the vessel.

Equally, when the vacuum in the vessel is being decreased after use, the diaphragm will revert from the second position to its first position again at a predetermined pressure differential across the diaphragm. Generally, the predetermined pressure differential will be substantially the same in either direction of the diaphragm movement.

The structure of the diaphragm itself is important. It is the radially arrayed elongate indentations which cause the diaphragm to adopt a first position or a second position by a quickly effected "snap action at a predetermined pressure differential across the diaphragm.

Preferably, the elongate slots each extend from a small "island" at the centre of the unsupported central area up to a position close to the supported periphery. The central island can advantageously be an indentation, for example circular, rectangular or square, which is preferably formed in the opposite side of the diaphragm to the elongate slots.

In preferred embodiments, the diaphragm is made from a thin circular metallic sheet of material with: i) an outer peripheral band for support against a switch component.

ii) an unsupported central area within which are formed, for example by stamping or pressing, elongate radially extending indentations, and iii) an island at the heart of the array of elongate indentations comprising a circular indentation formed, for example by stamping or pressing.

For a better understanding of the invention, reference will now be made, by way of exemplification only, to the accompanying drawings in which: Figure 1 is a vertical sectional view through a switch arrangement of the invention.

Figure 2 is a plan view of the diaphragm incorporated into the arrangement of Figure 1.

With regard to Figure 1, there is shown a switch arrangement comprising a standard electrical positive action type switch 1 mounted within an inner housing 2 by means of bolts 3,4 with the inner housing itself attached to an outer housing 5 by means of further bolts 6,7.

The outer housing 5 has formed therein a passageway 8 whose flange 9 is adapted for being secured to a vacuum system or chamber within which, for example, a coating process using sputtering or whatever, is being performed.

A circular diaphragm 10 is secured to the inner wall of the outer housing 5 by welding (or whatever) to form a leak-tight connection across the passageway 8.

The position of the diaphragm in the housings is such that it can impinge on a protruding switch actuator 11.

Figure 2 shows a plan view of the diaphragm from the direction of the vacuum chamber. It comprises an outer peripheral band 12 which is welded to the internal wall of the outer housing 5 to form an air tight connection thereto in the position shown in Figure 1. This band 12 stands proud of the surface of a central area 13 (as shown in Figure 1); the centre area 13 has embossed therein a series of radially extending elongate (depressed) slots or grooves 14 which extend from a position close to the inner edge of the band 12 to a central island 15. This central island is in the same plane as the central area but is defined by an upstanding ring 16.

The band 12, the depressed grooves 14 and the upstanding ring 16 can all be formed from a thin sheet of the diaphragm material, normally metallic, by stamping or pressing in one or more operations.

The diaphragm construction allows it and in particular the central island, to adopt two specific positions and to enable it to move rapidly, ie "snap-action", from a first position to its second position and to return to the first position at a particular pressure difference across the supported diaphragm.

The actual pressure at which the movement from one position to the other takes place can depend on the size of the diaphragm itself, the size of the elongate slots and the size of the central island.

In the diaphragm position shown in Figure 1, the system to which the flange 9 is attached is evacuated so that the positive action switch is "on" and allow current to flow to the system. When the system is being brought towards atmospheric pressure, however, the increased pressure on the side of the diaphragm nearest the system causes the diaphragm to "snap" to its other position, thereby depressing the switch actuator and cutting off the current to the system. The switch will only be re-actuated when the predetermined pressure difference across the diaphragm changes during re-evacuation of the system.

Claims (8)

1. An electrical switch arrangement which is activated by means of a pressure differential exerted across a diaphragm, wherein the diaphragm is a substantially planar sheet of material supported along its periphery and having in an unsupported central area a series of radially (arrayed) elongate indentations to cause the central portion to adopt a first position and rapidly move to a second position with a predetermined differential across the diaphragm.

2. An electrical switch arrangement according to Claim 1 incorporating a positive action switch.

3. An electrical switch arrangement according to Claim 1 or Claim 2 in which the diaphragm is supported across a passageway or nozzle which is associated with a switch and which is arranged for communication with a pressure or vacuum vessel.

4. An electrical switch arrangement according to any preceding claim in which the radially arrayed elongate indentations which cause the diaphragm to adopt a first position or a second position by a quickly effected "snap" action at a predetermined pressure differential across the diaphragm.

5. An electrical switch arrangement according to Claim 4 in which the elongate slots each extend from a small "island" at the centre of the unsupported central area up to a position close to the supported periphery.

6. An electric switch arrangement according to Claim 5 in which the central island is an indentation which is formed in the opposite side of the diaphragm to the elongate slots.

7. An electric switch arrangement according to any preceding claim in which the diaphragm is made from a thin circular metallic sheet of material with: i) an outer peripheral band for support against a switch component.

ii) an unsupported central area within which are formed, for example by stamping or pressing, elongate radially extending indentations, and iii) an island at the heart of the array of elongate indentations comprising a circular indentation formed, for example by stamping or pressing.

8. An electric switch arrangement according to Claim 1 substantially as shown in Figure 1 or Figure 2 of the attached drawings.