US3230333A - Capillary mercury switches - Google Patents

Description

Jan. 18, 1966 N. BERMAN CAPILLARY MERCURY SWITCHES 3 Sheets-Sheet 1 Filed March 14, 1962 INVENTOR.

NELSON HERMAN Jan. 18, 1966 N. BERMAN 3,230,333

CAPILLARY MERCURY SWITCHES Filed March 14, 1962 3 Sheets-Sheet 2 Fig.4?

I HYDROGEN 3 GAS United States Patent C 3,230,333 CAPILLARY MERCURY SWITCHES Nelson Ber-man, 6 Magnolia Drive, New Hyde Park, N.Y. Filed Mar. 14, 1962, Ser. No. 179,727 7 Claims. (Cl. 200-152) The present invention relates to improvements in mercury switches, relays, and other contact making devices.

In particular, it relates to mercury switches employing closed capillary tubes.

Hermetically sealed gas filled mercury switches are widely used for switching electrical circuits because the use of liquid contact surfaces results in long troublefree operation, freedom from electrical noise, no contact bounce, and low contact resistance.

The use of many mercury switches is limited to applications where they are always in a vertical or near vertical position, and where they are not subject to shock or vibration. Other switches of the type in which a solid dielectric separates a single pool of mercury into two pools when the circuit is opened do not have consistently high insulation resistance in the open circuit condition.

The objects of this invention are as follows:

(1) To provide an improved mercury switch which can be operated in any position.

(2) To provide a mercury-switch which is unafiected by shock and vibration.

(3) To provide a switch which can be operated rapid- 1y.

(4) To provide a hermetically sealed gas filled mercury switch which can be made in a very small size.

The invention will be more fully described with reference to the accompanying drawings. In the drawings:

FIG. '1 is a longitudinal section of a capillary mercury switch.

FIG. 2 is a longitudinal section of a normally open, panel mounted, capillary mercury switch.

FIG. 3 is a longitudinal section of a normally closed, panel mounted, capillary mercury switch.

FIG. 4 is a longitudinal section of a panel mounted relay including a capillary mercury switch.

FIG. 5 is a longitudinal section of a multiple tube capillary mercury switch.

FIG. 6 is a longitudinal section of a tubular diaphragm capillary mercury switch.

FIG. 7 is a plan view of a rotary cornmutating switch including capillary mercury switches.

FIG. 8 is a sectional view taken on line 88 of FIG. 7.

FIG. 9 is a longitudinal section of a multiple circuit capillary mercury switch.

FIG. 10 is a schematic of a crossbar matrix switch.

FIG. 11 is an electrical connection chart for the matrix switch of FIG. 10.

FIG. 12 is a longitudinal section of a magnet-ostriction capillary mercury relay.

Referring to FIG. 1, this embodiment of the invention is a normally open push button switch. It is comprised of a glass capillary tube 1 interposed between a bellows 2 and a metal capillary tube 3, and a second glass capillary tube 4. The capillary bore 5, of the metal. tube 3 is axially aligned with the bores 6 and 7 of the glass tubes and the diameters of the three tubes are essentially equal. The end of the glass tube 4 is closed. The glass tubes are attached to the metal tube and to the bellows by the glass to metal seals 8 and 9 respectively.

The end of the bellows away from the glass tube is also closed. Most of the volume of the bellows 2 is occupied by a cylindrical rod filler piece 10 made of a "ice material inert to mercury such as Teflon. The filler piece 10 has small projections 11 at the end adjacent to the glass capillary tube 1 so that the flow of mercury in and out of the capillary tube 1 is not impeded. The remaining volume of the bellows 2 and part of the volume of the glass capillary bore 7 are occupied by mercury 12. The remainder of the glass bore 7, all of the met-a1 capillary bore 5, and all of the glass capillary bore 6 are filled with a compressed gas, preferably hydrogen. The leads 13 and 14 are attached by solder 16 to the metal tube 3 and bellows 2 respectively.

In operation, the electrical circuit including the battery 17 and load 18 is completed by deflecting the bellows 2 decreasing internal volume of the bellows and forcing some of the mercury through the glass tube 1 and through the metal tube 3 into the glass tube 4. In order to keep the contact resistance low the bellows 2 and metal tube 3 are mad-e of a material that can be wetted 'by mercury, such as nickel.

T he elements are so proportioned that the end of the a mercury column is in a glass segment of the capillary channel in both the on and off positions. This precaution is taken to prevent malfunction of the switch under conditions of shock, vibration, or acceleration. In the off condition of the switch, a malfunction can i occur only if the mercury moves along the tube until it forms a conducting path between the metal tube 3 and the bellows 2. Since the mercury does not wet the glass, capillary force and surface tension of the mercury tend to keep the mercury in a single mass. Movement of the mercury mass along the capillary channel is prevented by the pressure of the gas in the space unoccupied by mercury. In the on condition of the switch, malfunction can occur only if the mercury column is disrupted. Disruption can occur only if a portion of the mercury moves along the capillary channel away from the bellows. Again, such movement is prevented by the combination of capillary force, surface tension and gas pressure.

In the configurations shown in FIGURES 1, 2, 3, 4, 5, 6, and 9, the invention incorporates a resilient member for changing the sealed volume of the switch. As shown, the portion of the switch undergoing the change in volume has a volume much greater than the volume of thecapillary channel. In order to prevent the device from behaving like a thermometer when temperature changes occur, a filler piece (10 in FIG. 1) which reduces the net volume is enclosed in the chamber of the resilient member. This filler piece could be eliminated by reducing the size of the resilient member to capillary dimensions. However, the construction shown is preferred for ease of mechanical operation and fabrication.

FIGURE 2 shows an embodiment of the invention which includes provision for mounting the switch of FIG. 1 in a panel. All of the elements of the switches shown in FIG. 1 and FIG. 2 are the same except that a bushing 19 having a flange 20 and an external thread 21 upon which is threaded the mounting nut 22 is interposed between the glass capillary tube 1 and the bellows 2. External circuit connections are made to the lead 23 and the bushing 19. The switch is a normally open push-button type operated by finger pressure on the bellows 2.

FIGURE 3 shows an embodiment of the invention which is a normally closed push button type switch. This embodiment is the switch shown in FIG. 2 modified by the addition of a mechanism which changes it from being normally open to being normally closed.

The bushing 24 corresponds to bushing 19 of FIG. 2, modified by the addition of a threaded shank 25 at the bellows end on which is screwed the cylinder 26 having an internal thread 27. Mounted in the cylinder by means of a pin 28 is a lever 29. Spring 30, positioned by spacer 30a, acts in combination with lever 29 to keep the bellows deflected until the button is depressed. The button 31 and spring 30 and spacer 30:: are retained in the cylinder 26 by the lip 32 formed by spinning over the edge of the cylinder 26. The switch is shown in the normally closed position with the mercury column 12 completing the circuit between the metal capillary tube 3 and the bushing 24.

An embodiment of the invention in the form of a relay is shown in FIGURE 4. The bushing 24 in FIG. 2 is replaced by bushing 33. This bushing has been counterbored to allow for recessed mounting of the capillary tubes. The bushing 33 has a threaded shank 34 at the bellows end on which is mounted the internally threaded cylindrical cap 35. Within the cap are the relay actuating elements, coil 36, armature 37, and spring 38, which, in conjunction with the switch capsule 39, operate in the conventional fashion as a normally closed relay. External connections to the relay coil 36 are made to the leads 40. The load circuit is connected to the lead 41 and the bushing 33.

In this invention the electrical circuit is completed by the mercury in a capillary channel. This channel can have dimensions equivalent to a circular diameter of from .005 to .040" with a preferred dimension about .010". This small diameter limits the amount of current which can be handled in a single contact making element. FIGURE shows an embodiment of the invention which provides multiple parallel paths for the current, thus increasing the amount of current which can be handled. In FIGURE 5 a single metal bellows 42 is sealed to the ceramic case 43. Shown in the case are four capillary elements 44 comprised of a metal capillary tube 45 between and in axial alignment with two glass capillary tubes 46 and 47. One end of the capillary element 44 is closed. The other end opens into the chamber formed by the bellows 42. The metal capillary tubes are connected to the lead 48 by solder 49. The lead 48 passes through the case 43 in a ceramic to metal seal 50. The capillary elements 44 are embedded in plastic 51 to improve the mechanical strength of the switch.

A filler piece 52 is contained in the bellows 42 to reduce the net volume of the bellows. The remainder of the bellows 42 is filled with mercury 53 and the mercury extends partially into the bore of the glass capillary tubes adajcent to the bellows. The remainder of the capillary elements 44 are filled with compressed gas, preferably hydrogen. External connections are made to the leads 48 and 48a. The switch is operated by deflecting the bellows 42.

FIGURE 6 shows another embodiment 55 of the invention. This differs from the embodiment shown in FIG- URE 1 in that a thin Walled resilient metal tube 54 is substituted for the bellows 2 of FIGURE 1. This switch is operated by applying pressure to the sides of the thin walled tube 54. The configuration of the other parts of the switch shown in FIGURE 6 differ somewhat from those shown in FIGURE 1 but there are no other functional differences.

The switch 55 shown in FIGURE 6 is used as the contact making element of the rotary commutating switch shown in FIGS. 7 and 8. In this embodiment of the invention the switches 55 are located in grooves in the baseplate 56. A flexible arm 57, loaded by the spring 58, is attached to the shaft 59 of the motor 60. A roller 61 is mounted in the end of arm 57 by pin 62. Operation of the motor causes the arm 57 to rotate and the roller 61 applies pressure to the resilient tube 54 of the switch 55 as it passes over the switch. Hence as the arm rotates the switches 55 are sequentially momentarily operated. The load connections to the leads 63 of the individual switches and the operation of the commutator switch for sampling signals from multiple external sources can be made in various ways well known to the art.

Another embodiment 64 of the invention is shown in FIG. 9. In this embodiment the switch shown in the first embodiment, FIG. 1, is modified by the addition of multiple alternate conducting and non-conducting capillary tube segments. In FIG. 9, the bellows 2, filler piece 10, glass capillary tube 1, and metal capillary tube 3, are the same as those shown in FIG. 1. The additional glass capillary tubes, 65, 66, 67, and the additional metal capillary tubes 68, 69, and 70, are joined together in axial alignment alternating a conducting with a non-conducting segment. The last segment is the closed end glass capillary tube 4. External leads 71 to 75 inclusive are connected to the bellows 2 and to the metal tubes. Two masses of mercury are contained in the switch. One 76 fills the bellows and extends into the glass segment 1. The other mercury mass 77 is entirely in the capillary channel 78 completley filling the segments, 68, 66, and 69, and extending partially into the glass segments, 65 and 67. The normal minisci positions are L, M, and N in FIG. 9. The portions of the capillary channel not occupied by mercury are filled with hydrogen.

Upon actuation of the switch, mercury 76 is displaced into the capillary channel 58. This movement of mercury compresses the gas between the two masses of mercury 76 and 77. The increased pressure causes the second mass 77 to move along the tube until the pressures in the two gas filled sections are equal. The amount of displacement of the two masses of mercury is controllable by the dimensional design of the bellows 2 and capillary segments. In the embodiment shown in FIGURE 9, after actuation one mass of mercury 76 completely fills the bellows 2, the glass segment 1, and the metal segment 3;

and partially fills the glass segment 65. The other mass 7 Condition Normal Actuated Closed. Open. Open. Closed.

It will be obvious to those skilled in the art that various other switching functions can be performed by proper selection of the number of capillary segments, amount, number and position of the mercury masses.

FIGURE 10 shows schematically the construction of a matrix switch using pluralities of switches similar to the multiple segment switches of FIGURE 9 and constructed and wired as shown. A rectangular array of any size is made by orienting the switches as shown and soldering the metallic segments 79 together at the points of intersection 82. Actuation of any two of the bellows 2 will complete a circuit. The positions of the mercury columns in metallic segments 81 prior to actuation is indicated at 80 in FIG. 10. After actuation the mercury column 80 forms a conducting path between metallic segments 81 and 79. FIG. 11 is a tabulation of some of the connections that can be made by actuation of two of the switches (1) to (8). g

Another embodiment of the invention is a relay utilizing the magnetostriction effect for displacing mercury. Certain metals have the property of changing their dimensions when magnetized. For example, iron-cobalt alloys will change longitudinally up to 96 parts per million. Electrostrictive materials such as barium titanate change their dimensions when subjected to an electrostatic field.

The manner in which the magnetostriction effect is utilized is described referring to FIGURE 12. A compartment is formed by two coaxial concentric shells 87 and 88, each having one end open. An electromagnetic coil 84 enclosed in a case 83 made of magnetostrictive material, preferably an alloy of iron and cobalt is located in and fills the peripheral compartment between the two shells 87 and 88. One end of the case 83 is sealed by the welds 94 to the plate 85. The ends of the coil 84 are attached to the insulated feed-through glass-to-metal-sealed terminals 86 which are located in plate 85. The plate 85 is also sealed by the welds 95 to the shells 87 and 88. A capillary switch capsule 89 is sealed by the Weld 92 in an opening in the center of the closed end of the inner shell 88. The open end of the capillary channel connects to the chamber 97 formed by the shells 87 and 88 and one end of the case 83. The chamber 97 is filled with mercury 91 and the mercury extends into part of the capillary channel 96. Foam rubber 90 fills the remainder of the space in shell 88.

When the coil 84 is energized it sets up an electromagnetic field which magnetizes the case 83. The length of the case increases and mercury is forced out of the chamber 97 into the capillary channel 96. While the amount of dimensional change due to magnetostriction is small, in this invention the dimensional change is, in effect, hydraulically amplified by an amount equal to the ratio of the area of the end of the case 83 to the area of the capillary channel 96. This ratio will vary with the design parameters chosen. However, a preferred and easily obtained ratio is 2,000 to 1. The variation of length of the mercury column in the closed capillary channel 96 is utilized in the manner described for the other embodiments of the invention, to open and close the circuit between the leads 93.

While a relay employing a magnetostriction element has been described this element can be replaced by an electrostrictive element, such as barium titanate without departing from the scope of this invention.

While there have been shown and described and pointed out the fundamental novel features of the invention as applied to preferred embodiments, it will be understood that various omissions and substitutions and changes in the form and details of the device illustrated and in its operation may be made by those skilled in the art without departing from the spirit of the invention. It is the intention, therefore, to be limited only as indicated by the scope of the following claims.

What is claimed is:

1. A switching device including in combination a capillary tube comprising an electrically conductive section and a nonconductive section, a variable volume reservoir, a supply of conductive fluid in said reservoir, said fluid supply comprising a portion of said fluid extending into said capillary tube and a solid slug of inert material having a low thermal coeflicient of expansion disposed in said reservoir.

2. A switching device including in combination a capillary tube comprising an electrically conductive section and a nonconductive section, a supply of conductive fluid comprising a portion extending into said capillary tube and magnetostrictive means acting on said fluid to move said portion between a position at which it contacts said conductive section and a position at which it is out of contact with said conductive section.

3. A switching device including in combination a capillary tube comprising an electrically conductive section and a nonconductive section, a supply of conductive fluid comprising a portion extending into said capillary tube and electrostrictive means acting on said fluid to move said portion between a position at which is contacts said conductive section and a position at which it is out of contact with said conductive section.

4. A switching device including in combination a capillary tube comprising an electrically conductive section and a nonconductive section, a variable volume reservoir connected to said capillary tube, a supply of conductive fluid in said reservoir and comprising a portion of said fluid extending into said capillary tube, said reservoir being formed at least in part of maignetostrictive material and means applying a magnetic fieid to said magnetostrictive material to vary the volume of said reservoir to move said extending portion of said fluid between a position at which it is out of engagement with said conductive portion and a position at which it is in engagement with said conductive portion.

5. A switching device including in combination a plurality of capillary tubes each comprising an electrically conductive section and a nonconductive section, respective variable volume reservoirs each having a deformable wall connected to said capillary tubes, respective supplies of conductive fluid in said reservoirs, each of said fluid supplies comprising a portion of said fluid extending into its associated capillary tube, means mounting said tubes in spaced relationship and movable means acting on said reservoir walls sequentially to move the respective fluid portions between positions at which they contact the associated conductive sections and positions at which they are out of contact with said conductive sections.

6. A switching device including in combination a capillary tube comprising a plurality of conductive sections separated by nonconductive sections, means closing an end of said tube, a variable volume reservoir connected to the other end of said tube, a supply of conductive fluid in said reservoir, said supply comprising a portion extending into said capillary tube, a discrete charge of conductive fluid separate from said supply disposed in said tube and gas filling the remainder of said tube, said reservoir being adapted to be actuated to move said extending fluid portion and said discrete fluid portion relative to said conductive sections whereby connections are selectively made and broken to said conductive sections in response to actuation of said reservoir.

7. A switching matrix including in combination a plu rality of lines and columns of intersecting capillary tubes, each of said tubes comprising conductive and nonconductive sections, respective supplies of conductive fluid connected to the ends of said tubes, said supplies comprising portions of said fluid extending into said tubes, respective discrete charges of conductive fluid separate from said supplies disposed in said tubes, gas filling the remainders of said tubes and means acting on said fluid in said tubes selectively to interconnect predetermined conductive sections.

References Cited by the Examiner UNITED STATES PATENTS 1,680,400 8/1928 Ulrey et a1. 200-112 X 2,472,082 6/ 1949 Armstrong 200122 2,566,369 9/1951 Putman ZOO-81.6 X 2,587,482 2/1952 Keller 200-87 2,621,268 12/1952 Lindstrom et al 20081.6

KATHLEEN H. CLAFFY, Primary Examiner.

ROBERT K. SCHAEFER, BERNARD A. GILHEANY,

Examiners.

Claims (1)

1. A SWITCHING DEVICE INCLUDING IN COMBINATION A CAPILLARY TUBE COMPRISING AN ELECTRICALLY CONDUCTIVE SECTION AND A NONCONDUCTIVE SECTION, A VARIABLE VOLUME RESERVOIR, A SUPPLY OF CONDUCTIVE FLUID IN SAID RESERVOIR, SAID FLUID SUPPLY COMPRISING A PORTION OF SAID EXTENDING INTO SAID CAPILLARY TUBE AND A SOLID SLUG OF INERT MATERIAL HAVING A LOW THERMAL COEFFICIENT OF EXPANSION DISPOSED IN SAID RESERVOIR.

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