Liquid Type Modular Electrical Switch

Abstract

A modular electrical switch includes a fluid-tight enclosure into which conductive contacts extend to provide selective switching in cooperation with a conductive liquid, such as mercury, contained within a cavity in the enclosure, depending on the position of the switch module. The contacts and the connections thereto are formed by metallic deposits on a dielectric substrate. The cavity can be of several different shapes including polygonal and toric, the liquid resting, due to gravity, in the lowermost corner of the cavity in the former embodiment.

Description

FIELD OF THE INVENTION

The present invention generally relates to modular electrical switches employing a liquid conductor, such as mercury-type switches.

BACKGROUND OF THE INVENTION

Switches of the type referred to above take a number of different forms, switching generally being provided by rotation of the unit and the liquid, as stated, usually being mercury. For example, in one switch of this type, mercury is contained in a fluid-tight swinging bulb to which electrodes are attached. A further such switch includes a mercury-containing cylindrical bulb inside of which electrodes are electomagnetically rotated. Another switch of this type is formed by a fluid-tight toric or toroidal glass tube which contains a mass of mercury and into which projects an electrode assembly. The mercury moves responsive to swinging or rotational movements of the tube to make selective contact with the various electrodes.

Although these switches are relatively simple, the relatively large size and mass of the switches is a disadvantage and can render the switches unsuitable for certain applications.

SUMMARY OF THE INVENTION

In accordance with the present invention, a modular electrical switch is provided which is of substantially reduced size and weight as compared with prior art switches, but, nonetheless, enables complex switching to be carried out.

In its broader aspects, the swtich of the invention comprises a liquid-tight, insulating enclosure which contains a conductive liquid and into which conductive contacts extend, the contacts being formed by a metallic deposit on a dielectric substrate. The metallic deposits can, for example, be thin metallic layers formed by printed circuit techniques, thereby making it possible to substantially reduce both the size and cost of the device.

According to one important embodiment of the invention, the fluid-tight enclosure provides a toric cavity and the contacts are located about the periphery of the cavity. This arrangement permits the use of a large number of contacts and hence provides a correspondingly large number of switching states.

Another advantageous embodiment, which is particularly intended for use with relatively weak signals, the contacts are covered or coated with a conductive deposit which can be wetted by the conductive liquid, the additional deposit permitting the passage of very weak currents. Where the conductive liquid is mercury, these deposits can be made up of platinum, nickel, chrome, tungsten or other metals which do not form an amalgam with mercury.

Other features and advantages of the invention will be set forth in or apparent from, the description of the preferred embodiments of the invention found hereinbelow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevation, partially broken away, of a first embodiment of the invention;

FIG. 2 is a sectional view taken generally along line II--II of FIG. 1;

FIG. 3 is side elevation, partially broken away, of a second embodiment of the invention;

FIG. 4 is a sectional view taken generally along line IV--IV of FIG. 3;

FIG. 5 is a side elevation, partially broken away, of a third embodiment of the invention;

FIG. 6 is a sectional view taken generally along line VI--VI of FIG. 5; and

FIG. 7 is a perspective view illustrating an assembly of switches similar to those of FIGS. 1 and 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIGS. 1 and 2, a modular electrical switch in accordance with a first embodiment of the invention is shown. The switch includes a dielectric substrate 10 with a series of conductive connections 12 located thereon, the connections 12 being formed by metallic deposits on substrate 10. The connections 12 are adapted to be connected, through connector portions 12a, to external circuitry by conventional lead wires (not shown) and include contact portions or contacts 12b which form a discontinuous conductive network, as illustrated. The connections 12 are preferably formed as thin layers using printed circuit techniques and employing copper, or by conventional photoengraving techniques using platinum, chrome-nickel or tungsten. Connections 12 can also be formed in even thinner layers using silk screening techniques. Substrate 10 can, for example, comprise a polyester with glass fibers incorporated therein.

As is also illustrated, portions of contacts 12b extend into a fluid-tight housing or enclosure 14 formed by a rectangular insulating cup 16. Cup 16 is secured to substrate 10 by suitable means such as gluing, using a bead of epoxy resin as indicated at 20 in FIG. 2, and defines a cavity 18 The enclosure 14 contains a conductive liquid formed by a drop of mercury 20. The switch is assumed to be vertical in FIG. 1, and the mercury drop 22 thus occupies the lower corner of rectangular cup 16 where it is held by gravity.

In the example illustrated, there are six connector portions 12a arranged so that their associated contacts 12b form three inter-electrode gaps or "posts" 24, 26, 28 in three corners of cup 16 which are bridged by mercury drop 22 when the switch is rotated so that the gap in question is lowermost, i.e., in the position shown for gap 26 in FIG. 1. The gaps 24 and 26 are formed by the ends of four convergent contacts 12b, one contact of each being the end of the arm of a generally cruciform shaped central contact as shown. The other gap 26 is formed by two contacts, viz, the foot of the cruciform shaped central contact and a straight line contact portion, as shown. It will be appreciated the amount of mercury, i.e., the size of mercury drop 22, depends on the space or gap defined at 24, 26 and 28, although in a specific practical embodiment, the volume of drop 22 is several cubic millimeters.

The switch of FIG. 1 does not have to be vertical to enable proper operation and, in fact, can be inclined up to about 50.degree. to the vertical and still function as intended. The precise maximum value of inclination, of course, depends on a number of technical or physical relationships, the frictional forces exerted by the drop 22 on the surface of the cup 16 depending, for example, on the substance used to make the cup.

In order to reduce the risk of gradual oxidation of conductive contacts 12b, it is advantageous to deposit a suitable metal thereon which does not form an amalgam with mercury drop 22 and is capable of wetting thereby. Alternatively, (or additionally) a partial vacuum can be created in cavity 18 or this cavity can be filled with a neutral gas.

As mentioned hereinabove, the switch of the invention is particularly advantageous in switching microcurrents (currents of several milliamperes) but when so used, it is necessary, as a practical matter, that the contacts 12b be covered with a thin conductive layer providing good electrical contact with mercury drop 22, the resistance between drop 22 and contacts 12b preferably being held to value on the order of one milliohm. If contacts 12b are copper, this purpose may be served by electrochemically depositing thereon a suitable metal such as platinum, chrome or nickel. Alternatively, tungsten can be sprayed on contacts 12b using conventional tungsten plasma techniques.

The switch of the invention is very small in size and low in cost relative to conventional switches of this type and, with this simplicity, enables complex switching to be performed thereby making it attractive for use, as an example, in telephonic switching. It is noted that cup 16 need not be rectangular and other polygonal shapes can be used to provide a number of interelectrode gaps, corresponding to gaps 24, 26 and 28, equal to the number of angles of the polygon. However, it will be understood that there is a limit to the number of sides the polygon can have and it has been found that the angle of rotation between adjacent gaps should be at least 30.degree..

Referring to FIGS. 3 and 4, a further embodiment of the invention is illustrated which includes a fluid-tight unit or housing 30 defines a toric or toroidal cavity 32 into which a plurality of radial contacts 34b extend. Radial contacts 34b are part of corresponding connections, generally denoted 34, which terminate in connector portions 34a. The unit 30 houses a mercury drop 36 and is mounted on a substrate 38, and the switch of FIGS. 3 and 4 is otherwise similar to that of FIGS. 1 and 2. As illustrated, the volume of mercury drop 36 is such as to provide connection of three adjacent contacts 34b although, of course, this volume can be reduced to provide connection between two contacts only.

The embodiment of FIGS. 3 and 4 provides a particularly large number of switching gaps or posts for mercury drop 36 simply by multiplying the number of conductive connections 34. Switching is accomplished, as in the embodiment of FIGS. 1 and 2, by merely rotating the switch, the mercury drop 36 remaining stationary and providing connection between the next set of electrode contacts 34b rotated into the position shown in FIG. 3. The embodiment of FIGS. 3 and 4 is particularly useful in generating pulses and, for example, measuring rotational speeds.

Referring to FIGS. 5 and 6, the embodiment shown therein is closely related to that shown in FIGS. 3 and 4 and like elements have been given the same numners as in FIGS. 3 and 4 with prime superscripts. In FIGS. 5 and 6, an annular cup 40 replaces the enclosure of FIGS. 3 and 14 and defines a circular cavity 42. Substrate 38' includes a concave face 38a' the center of which is coaxial with cavity 42. Electrodes 34' are also curved to conform to the shape of the concave face 38a' of substrate 38' as shown in FIG. 6.

In operation, with the switch horizontal, the mercury drop 36' is located in the center of cavity 42 as illustrated. In this embodiment, it is advantageous to, for example, connect all even electrodes 34' to the same pole and all odd electrodes 34' to another pole so that a current path can be established by swinging the switch in any direction.

Referring to FIG. 7, an assembly 50 of a series of switches similar to those of FIGS. 1 and 2 is shown. Flexible lead wires 52 are provided and the switches are held together by rods (not shown) which extend through the assembly and on to the ends of which are screwed nuts 54.

It will be appreciated that the invention is not limited to the embodiments described hereinabove and that various modifications and variations can be effected in these embodiments without departing from the scope and spirit of the invention. For example, a polygonal half cup may be combined with a toric-shaped half cavity and an appropriate arrangement of contacts provided. Further, referring again to the embodiment of FIGS. 3 and 4, it is possible to locate a branched conductive network in the center of housing 32, the branches cooperating with the mercury drop 36 and two electrodes 34 to provide switching connections. These modifications are, of course, non-limiting and are only examples of those possible.

Claims

I claim:

1. A modular electrical switch comprising a dielectric substrate, electrical contacts located on said substrate, a fluid-tight insulating enclosure secured to said substrate and containing a conductive liquid and said electrical contacts extending into said enclosure, said contacts comprising thin metallic layer deposits on said dielectric substrate and said conductive liquid, in the switching position thereof, providing a conductive path between a pair of neighboring electrical contacts.

2. A switch as claimed in claim 1 wherein said enclosure defines a toric cavity therein, said contacts comprising radial contacts located about the periphery of said toxic cavity.

3. A switch as claimed in claim 1 wherein said enclosures defines a cavity of polygonal shape.

4. A switch as claimed in claim 1 wherein said dielectric substrate includes a concave face, said enclosure being mounted on said concave face.

5. A switch as claimed in claim 1 wherein said contacts provide plural connection areas each including at least two contacts positioned relative to one another such that the liquid completes an electrical connection therebetween.

6. A switch as claimed in claim 1 wherein said contacts include a conductive deposit thereon capable of wetting by the conductive liquid.

7. A switch as claimed in claim 1 wherein said thin layers comprise printed circuits.

8. A switch as claimed in claim 1 wherein said enclosure is filled with a neutral gas.

9. A switch as claimed in claim 1 wherein a partial vacuum is provided within said enclosure.