US 3673524 A
A bistable magnetically operated mercury switch is disclosed which comprises a magnetic piston contained in a hermetically sealed chamber along with a globule of mercury. As the piston is moved from one end of the chamber to the other end under the influence of an external magnetic field, the mercury is displaced through an aperture in the spindle to the opposite end of the chamber where it electrically connects terminals.
Description (OCR text may contain errors)
United States Patent Lowry 1 June 27, 1972 54] PISTON MERCURY SWITCH FOREIGN PATENTS OR APPLICATIONS 72 Inventor; T n Ni h l L Ge Town- 443,289 4/ i927 Germany ..335/52 ship, Delaware County, Ohio Primary Examiner-Harold Broome Assign: Telephone Labomofies, W Attorney-R. J. Guenther and James Warren Falk Murray Hill, Berkeley Heights, NJ.
22 F] d: M 11 17 1971 I 1 l e m 57 ABSTRACT I l.N.: 12,184 [2 1 App 0 5 A b1stablc magnetically operated mercury sw1tch 1s d1sclosed which comprises a magnetic piston contained in a hermeti-  U.S. Cl ..335/52, 200/152 cally sealed'chamber along with a globule of mercury. As the [5 1] Int. Cl. ..H01h 29/02 piston is moved from one end of the chamber to the other end  Field of Search ..335/47, 48, 49, 51, 52, 50, under the influence of an external magnetic field, the mercury 335/53, 54, 55, 56, 62; ZOO/152.9, 153 W is displaced through an aperture in the spindle to the opposite end of the chamber where it electrically connects terminals.
 References Cited UNITED STATES PATENTS 6 Claims, 3 Drawing Figures 1,010,620 12/1911 Crumpton .335/52 PISTON MERCURY SWITCH FIELD OF THE INVENTION The present invention relates generally to electric switches and more particularly to mercury switches wherein mercury is displaced or moved within the switch chamber to complete an electric circuit between electrical terminals within the switch.
BACKGROUND OF THE INVENTION The desirability of mercury switches which may mount in any position, which are not fragile, which can be hermetically sealed and which are simple in structure has long been recognized and the prior art discloses mercury switches which achieve these goals with varying degrees of success. One prior art mercury switch contains mercury having colloidal iron dispersed therein (magnetic mercury); the mercury may then be moved from one part of the switch chamber to another part through a small orifice under the influence of an externally applied magnetic field. The surface tension of mercury prevents the magnetic mercury from freely flowing through the orifice; this permits the switch to be mounted in any position. However, if the switch is hermetically sealed and unevacuated, pressure equalization means must be provided to keep the pressure on either side of the orifice equal, as the magnetic mercury is moved through the orifice. If the chamber is evacuated it is most likely made of glass, which is fragile, and requires special packaging. In addition colloidal dispersions of iron particles in mercury have a tendency to settle out of the mercury.
Another prior art mercury switch contains two globules of magnetic mercury, one in each of two adjacent and horizontally oriented chambers. The area joining the two chambers is not wettable by mercury and this, in combination with the high surface tension of mercury, prevents the two mercury globules from normally contacting each other. By the application of an external magnetic field, the magnetic mercury globules are attracted and contact each other, closing an elec trical circuit through the mercury. This switch may be hermetically sealed and need not be evacuated, for the deformation of the two globules of magnetic mercury under the influence of the externally applied magnetic field creates no need for pressure equalization within the switch. However, the switch may only be mounted in a horizontal position and the colloidal iron particles tend to settle out of the mercury.
A third prior art mercury switch contains a pool of mercury upon which a magnetic washer floats, partially supported by a corrugated spring washer. An externally applied magnetic field moves the washer into the pool of mercury, displacing mercury to form an arcuate bridge between two electrodes. This switch may also be hermetically sealed and need not be evacuated as the mercury is displaced rather than moved by pressure. This switch may be mounted in other than a horizontal plane, but it is still position sensitive and, for instance, cannot be mounted upside down.
Accordingly it is an object of my invention to provide a mercury switch which is not fragile, which may be hermetically sealed, which is simple in structure, and which can be mounted in any position.
SUMMARY OF THE INVENTION The above and other objects are attained in an illustrative embodiment of my invention in which a mercury switch comprising a cylindrical hermetically sealed switch chamber, made of a material not wetted by mercury, has electrical terminals extending into one end portion of the switch chamber. The chamber contains a quantity of mercury and an apertured piston made of magnetic material and movable into either end portion of the switch chamber. The piston is made of a material not wetted by the mercury. To move the piston, a magnetic field is applied externally to the switch chamber by an energized coil. When the magnetic piston is moved into the end portion of the switch chamber occupied by the mercury, the mercury is displaced through the aperture to the opposite end portion, thereby completing an electric circuit between the electrical terminals.
In accordance with an aspect of my invention the piston is slidably positioned within the chamber, the outer diameter of the piston approximating the inner diameter of the chamber. The piston and the mercury together completely occupy the internal volume of the chamber; advantageously the piston and the mercury occupy substantially equal volumes within the chamber.
In the operation of a switch in accordance with my invention, the piston and the mercury reverse positions within the chamber. Unlike some prior art switches, in a switch in accordance with my invention the piston does not merely force the mercury into a different position within the chamber; the piston and the mercury actually reverse their positions. This is attained, in accordance with another aspect of my invention, as discussed above, by causing the mercury to flow through the constricted aperture in the piston.
Because the aperture through the piston is constricted, because the mercury has a high surface tension, and because the piston and the mercury together completely fill the inner volume of the chamber, the mercury and the piston will remain in either stable position without the necessity for a continuously applied magnetic field or any internal spring or other locking element. This is true regardless of the positioning of the chamber.
It is accordingly a feature of my invention that an electric switch include an apertured piston and a liquid nonmagnetic conductor having a high surface tension, the piston and the conductor together completely occupying the internal volume of the switch chamber. In this way neither the piston nor the liquid conductor can move separately; the piston can only move by forcing motion of the liquid conductor and similarly the liquid conductor can only move when the piston itself moves.
It is another feature of my invention that the aperture through the piston be sufficiently constricted that the high surface tension of the liquid conductor prevents any of the liquid conductor from passing through the aperture regardless of the physical positioning of the chamber.
It is a further feature of my invention that the piston be slidably positioned within the chamber, whereby movement of the liquid conductor can only occur through the constricted aperture in the piston.
It is a further feature of one specific embodiment of my invention that the piston and the liquid conductor occupy substantially equal volumes within the switch chamber, whereby operation of the switch is effected by reversing the physical positions of the piston and the liquid conductor within the switch.
DESCRIPTION OF THE DRAWING The above and other objects and features of my invention will become more apparent from the following detailed description of the accompanying drawing in which:
FIG. I is a partial sectional view of the switch before the mercury is introduced;
FIG. 2 is a sectional view taken on the axis of the cylindrical housing showing the position occupied by a magnetic piston and the mercury when the switch is in the open position; and
FIG. 3 is a sectional view, similar to FIG. 2, illustrating the switch in the closed position.
DETAILED DESCRIPTION Referring now to FIGS. 1 and 2 in the accompanying drawing, the reference numeral 10 denotes the switch housing in the form of an elongated cylinder fabricated of a nonmagnetic and nonconductive material not wetted by and having low solubility with mercury, which may advantageously be formed to hermetically seal the switch. One such material is alumina (A1 0 A pair of terminals 1 I extend through one end wall of the cylinder of housing 10. A piston 12 containing an aperture 12a is fabricated of a magnetizable material, not wetted by and having low solubility with mercury. The piston 12 is slidably mounted within the switch housing so as to be movable along the axis of the switch housing 10 into either end portion thereof.
Referring to FIG. 2, housing 10 contains a quantity of a liquid conductor 23 such as mercury sufficient to substantially fill the remainder of switch housing 10 not occupied by piston 12. The aperture through piston 12 is designed with a constriction such that under normal handling of the mercury switch the surface tension of mercury will not permit mercury 23 to freely pass through the aperture, regardless of the position in which the switch is mounted. Aperture 12a through piston 12 may be of many shapes including biconical or hourglass, though an hourglass shape is shown in the present invention. Typical dimensions of aperture 12a that will preclude mercury 23 from normally flowing through aperture 12a are: a diameter of 0.035 inch at the widest portions of hourglass aperture 12a and a diameter of 0.017 inch at the constriction of hourglass aperture 12a. Surrounding housing 10 is a solenoid winding 14 whose axis coincides with the axes of the housing and of piston 12. With a single solenoid 14 which extends substantially the entire length of housing 10, piston 12 should be made of a material exhibiting residual magnetism such that after coil 14 is deenergized, the piston will be propelled to one or the other end of the chamber. Thus when solenoid 14 is selectively energized by potentials +V and V, as shown in FIGS. 2 and 3, the residual magnetism in magnetic piston 12 interacts with the magnetic field created by the energization of winding 14 to move piston 12 from one end of switch housing 10 to the other end. One such material is steel.
Alternately, piston 12 may be made of iron which retains practically no residual magnetism, in which case coil 14 should be center tapped (not shown). The center tapped coil with either one or the other of its external ends energized will thus prevent a soft iron piston 12 from centering itself between the coil ends.
The external diameter of piston 12 should be slightly smaller than the inside diameter of switch housing 10 to prevent piston 12 from binding but should not be so large as to allow seepage of mercury past the piston. Advantageously, the axial length of piston 12 should be approximately one-half the internal length of housing 10.
Let us assume that the mercury switch is initially in the open position, as shown in FIG. 2. Piston 12 occupies the end portion of housing 10 adjacent terminals 11 while mercury globule 23 occupies the portion of housing 10 remote from terminals 11. To operate the mercury switch from the open position (FIG. 2) to the closed position (FIG. 3), winding 14 is energized by a power supply (not shown) with potential +V applied at its upper end and the potential V applied at its lower end, as shown in FIG. 3. The magnetic field created by the energization of winding 14 interacts with magnetic piston 12, creating a force which moves piston 12 to the upper end of switch housing 10. As piston 12 moves upward, mercury 23 is displaced through the aperture in piston 12 to the lower half of switch housing 10 where the mercury 23 makes an electrical connection between terminals 11. When the energization potential applied to coil 14 in FIG. 3 is removed, the switch will remain in the closed position for the high surface tension of mercury prevents mercury 23 from normally flowing through aperture 12a.
To open the mercury switch coil 14 is momentarily energized with the potential -V applied at its upper end and the potential +V applied at its lower end, as shown in FIG. 2. The reversed magnetic field created by energized coil 14 creates a force which now forces piston 12 downward, displacing mercury 23 to the upper portion of switch housing 10 as shown in FIG. 2. Again, the high surface tension of mercury prevents mercury 23 from normally flowing through aperture 12a.
It is to be understood that the above-described arrangement is merely illustrative of the numerous and varied other arrangements which may constitute applications of the principles of my invention. Such other arrangements may readily be devised by those skilled in the art without departing from the scope of my invention.
What is claimed is:
1. An electrical switch comprising a closed switch chamber having two end portions,
electrical conductors communicating with one of said end portions of said chamber,
a piston having an aperture and slidably placed in said one end portion of said chamber,
a quantity of liquid conductor in another of said end portions, the surface tension of said liquid conductor cooperating with said piston aperture in any physical orientation of said switch to fix said liquid conductor in said other end portion, and
means for moving said piston to said other end portion of said chamber to force said liquid conductor through said aperture, whereby said liquid conductor and said piston reverse positions within said chamber and complete an electrical connection between said electrical conductors when said liquid conductor occupies said one end portion.
2. An electric switch in accordance with claim 1 wherein said liquid conductor is mercury and wherein said quantity of mercury and said piston occupy substantially equal volume within said chamber.
3. In an electric switch, the combination comprising a closed switch chamber having two end portions,
a pair of electrical terminals extending into one of said end portions of said chamber,
a magnetizable piston slidably mounted in said one end portion of said chamber, said piston having an aperture therethrough,
a quantity of mercury in another of said end portions of said chamber, the surface tension of said mercury cooperating with said piston aperture in any physical orientation of said switch to fix said mercury in said other end portion, and
winding means exterior of said chamber and energizable for applying an axial magnetizing force to move said piston into said other end portion forcing said mercury through said aperture in said piston to said one end portion into physical contact with said terminals for completing an electrical connection therebetween.
4. The electric switch of claim 3 wherein said piston is made of a material nonwettable by said mercury.
5. The electric switch of claim 4 wherein said switch chamber is constructed of a material unwettable by said mercury.
6. An electric switch comprising a closed cylindrical switch chamber having two end portions, said switch chamber being constructed of a nonmagnetic material nonwettable by mercua pair of electrical terminals extending into an individual one of said end portions,
a magnetic piston slidably positioned in said chamber for occupying any one of said end portions, said piston being nonwettable by mercury and having an aperture therethrough communicating with said end portions of said chamber,
a quantity of mercury disposed within said chamber other than at said one of said end portions occupied by said piston and sufficient to substantially fill the internal volume of said chamber not occupied by said piston, said mercury and said piston occupying substantially equal volumes within said chamber, and the surface tension of said mercury cooperating with said nonwettable piston aperture in any physical orientation of said switch to fix said mercury other than at said one of said end portions occupied by said piston, and
winding means axial of said chamber and energizable for applying a magnetic field to move said piston, whereby said mercury and said piston reverse positions within said chamber to bring said mercury into physical contact with said terminals when said mercury occupies said individual one of said end portions and to open an electrical connection between said terminals when said mercury occupies other than said individual one of said end portions. 5