US3002069A - Electric switch - Google Patents

Description

Sept. 26, 1961 c. A. BURRUS ELECTRIC SWITCH Filed Dec. 29, 1959 FIG. 3

T0 QC. SOURCE Zla PULSE 0U TP U T wvewroe By C. A. BURRUS A T TORNEV United States Patent 3,002,069 ELECTRIC SWITCH Charles A. Burrus, Red Bank, NJ., assignor to Bell Telephone Laboratories, Incorporated, New York, NY, 'a corporation of New York I Filed Dec. 29, 1959, Ser. No. 862,525 1 Claim. (Cl. 200--112) This invention relates to electric switches and, more I particularly, to electric switches of the mercury contact type. I 7

An object of this invention is to provide an improved mercury contact for use in an electric switch. 7

Another object of the invention is to provide an improved mercury contact switch capable of extremely rapid cyclical operation.

,Still another object of the invention is to provide an improved mercury contact switch which is particularly adapted to form the center conductor of an electric coaxial line. s

A further object of the invention is toprovide an improved mercury contact switch for use in producing a train of pulses each of very short duration and having extremely fast rise time.

These and other objects of the invention are accomplished by mounting a bifurcated member at the bottom of an essentially cylindrical glass envelope or housing of an electric switch. The glass envelope is closed at each end and its lower portion contains a pool of mercury surrounding the bifurcated member which is of such dimensions that the upper ends of its forks project slightly above the surface of the pool of mercury. Due

to the effects of surface tension and capillary action, a thin section of mercury is formed between the forks in an elevated position with respect to the surface of the pool as is more fully described hereinafter. The elevated section of mercury functions as one of the two contacts of this switch.

The other contact of the switch is constituted by the tip of a movable armature'which is suspended from the top of the glass envelope in such a manner that its lower end or tip extends into the elevated section of mercury but deos not quite reach the surface of the pool. This armature is adapted to be electromagnetically controlled or operated so that its lower end will swing transversely through the elevated mercury section; The movement of the armature through the mercury section is facilitated by providing the end of the armature with a knife like edge.

During the operation of this switch, the armature cyclically swings back and forth rapidly between the forks of the bifurcated member and into and out of the elevated mercury section. When the armature is in the section of mercury, an electric connection is made. This connection is broken when the armature swings out of the mercury section. Thus, the operating time consumed in making and breaking a connection is only the few millimicroseconds required for the knife-edge of the armature to slice through the thin elevated section of mercury. It is to be noted that two connections are made FIGS. 3 and 3A are sectional viewsof the lower por- 3,002,069 Patented Sept. 26, 1961 ice tion of the switch showing a modified construction thereof; and

FIG. 4 is a schematic diagram partly in section illustrating the manner in which the switch of FIG. 1 is incorporated in a discharge line type of pulse generator.

While the invention is not limited to a switch of any given size or proportions, it should be noted that this switch is particularly useful when it is connected in series with the center conductor of an electric coaxial line. For this purpose, the switch may be made with extremely small dimensions, and it should therefore be understood that the figures shown in the drawing are greatly enlarged in order to facilitate a clearer comprehension of'the construction ofthe switch.

The illustrative embodiment of the invention shown in FIG. 1 is represented as an electric switch 1 having an essentially cylindrical glass envelope or housing 2 which is closed at each end. In this embodiment of the invention, the envelope is about one and three-eighths inches long and has an outside diameter of approximately three-sixteenths of an inch. Two terminals 3 and 4 are mounted in opposite ends of the envelope 2 with a portion of each extending inside the envelope 2 and another portion projecting outwardly therefrom. These terminals 3 and 4are electrically conductive and are made of any appropriate material, such as an alloy of nickel and iron,

, having substantially the same coefficient of expansion as the glass envelope 2 so that the joints between the terminals 3 and 4 and the envelope 2 will form a gas-tight seal. Prior to the sealing operation, a suitable gas, such as hydrogen is introduced inside the envelope 2 under high pressure for the purpose of improving the operating characteristics of the switch 1 and for prolonging its useful life. Two electric conductors 5 and 6 are connected respectively to the terminals 3 and 4 in any suitable manner. These conductors 5 and 6 constitute part of an electric circuit that is controlled by the switch-1. The portion of the lower terminal 3 that extends inside the envelope 2 supports a U-shaped envelope 7 of magnetic material which is not wettable by mercury. This member 7 is securely fastened to the terminal 3 in any convenient manner. The interior bottom portion of the member 7 serves as a base upon which is fixedly mounted, in any suitable manner, a bifurcated nonmagnetic member 8, having a thickness of between three fthousandths of an inch and one hundredth of an inch. These members 7 and 8 are almost completely submerged in a pool of mercury 9 contained in the bottomof the envelope 2 which serves as a reservoir.

As is indicated in the drawing, a small section 10 of mercury is raised or elevated above the surface of the pool 9 and is supported in the space between the forks of the member 8 due to the effects of surface tension and capillaryaction. In order to facilitate wetting of ,the forks of the member 8 by the mercury, the member 8 is. made of copper coated with platinum. In this embodiment of the invention, the inside spacing between the forks of the member 8 is about two hundredths of an inch and the top of the elevated mercury section it) is about four hundredths of an inch above the surface of the mercury pool 9. As was stated above, this minute elevated met- I cury section 10 constitutes one of the two contacts of the switch 1.

5f the elevated mercury section and the surface of the pool of mercury-9: In-this embodiment'of the invention, the bottom of the tip 12 extends about two hundredths of an inchinto the elevated mercury section 102' For the purpose of'facilitating' the movement of the armature 11 through the mercury section 10,. its lower end is formed in a sharp, tapered point'or tip'12 and is provided with a knife-like edge so that it can easily and quickly slice through the mercury section Ill-with aminimum of resistance. Since the tip 12' forms the other contact of the switch 1, it is coated with anv appropriate material, such as platinum, so that it can be easily wetted by. the mercury. The 'armaturefil'l is joined to the terminal. 4 by a section 13. of spring steelwelded'thereto so.

as. to increase its flexibility andthereby to increase. the

rapidity of its vibration or. movement.

Movement of the reed or armature 11; is. effected by means of a driving coil or winding 14. whichisfconnecte'd' to a. source 14a of alternating electric. curreutihaving; the:

same frequency as the. resonantfrequency of. the. reed.

.11, which, in this example, isone kilocycle. By thus.

using an alternating currentsupply 114a having the; same frequency as the resonant frequency of the reed 11,,it is possible for the reed -11 to. obtainits maximum. amplitudev ofsswing while it is vibrating thereby insuring thatitwill Itv shouldv beknotedthat the upright portions of. the. U.-Shaped morn-- swing completely away from. the mercury.

the-drawing for the purpose-of: simplicity,.itaisto be-understood that the coil 14 may actually consist of 'a sole-- noid; having a large number. oflturnss Thexdriving action of the. coi1;14 is assistedbytwo per.- manent' magnets 15 and 16 which; are. located outside the. glass" envelope 2. in close proximity to the pool 9 of. mercury. The magnets. 15 and16. are-.disposedon opposite' sides of the BRVGIOPEfZ'Wlth their endsafacing the broad sides of the LI-shaped: member 7,..which, ast-was stated above, is made of magnetic material. The magnets 15 and 16 are further arranged; so? that their ends which are adjacent to the envelope 2. are: of opposite polarity. Due to the magnetic forceinduc'ed by the :magnets-v15 and 16, the two upright portionssoi the u-shaped member 7 function aspole-pieces.

At this point, it is appropriate to state that the function of the U-shaped' member 7, which is'of'ma'gnetic material, is to enhance the fields of the externalmagnets 15. and 161- If desired, the member 7 can beomitted provided stronger magnets are substituted for. the magnets 15 and 16. Such a modification of the interior'constructionbf. the switch 1 is illustrated in FIGS. 3- and 3A. In this form of'the switch 1, it is convenient to havethe bifur-' cated member 8' directly supported on, or'attached' to, the upper end of the lower terminal 3.

From the above description of the structure of theswitch 1, it can be understood that the'electric pa'thbetween the leads 5 and 5' is closed through the switch 1' thd mercury section 10. It isto be notedthat'theplatinum coating on the'tip 12' is readily wettable' by'the mer oury" thereby assuring that good electric contacts are made. When the tip 12 moves away, themercury'scction 10 becomes broken or disrupted but it.quickly resumes: its elevatedposition. Asthearmature 11 swings back, its up 12 again enters the mercury section 10 and briefily re establishes the electric connection. Thi's connection is ofvery short duration because the.- tip 12 quickly slices through the extremely thin mercury section. 10. Since the-amount of mercury contained initheelevatedlsection 10 is so'minute and is so thin, it presents negligible resistance to the passagemf the tip 12 and, consequently,;

' ductor of a coaxial line since it can thenfunction as a pulse generator. for producing pulses; with extremely fast rise time and of very shortdurations The manner in which the switch 1 is installed for this purpose is illus trated in FIG. 4 which shows a discharge-line type of pulse generator comprising an open-circuited coaxial'line constituted by an outer cylindrical conductor 17 of non magneticmaterial surrounding an inner-coaxial conductor 18. to conductors S and 6, the terminals 3 and 4 are now connected in serieswith the inner coaxial conductor 18.

This can be done in any convenient-manner, such asby welding. The"function-performedby the magnets 15 and 15', shown-in FIG. 1, is' accomplished by'similar magnets" 19 and 20 which" are attached to the outer coaxial" con-- doctor 17. v

In this embodimentof'the invention, the driving coil 14 of FIG. 1 is. replacedby a driving sol'enoidZl formed around the outside ofthe'outer conductorl? andhaving switch terminal 4", is also connected througharesistor'n' to a source 23 ofdirect currentvoltage which applies a" charge to this open-ended coaxial line.17-18; Djure ing operation, the charged coaxial line 17-18 iscyclica'h 1y discharged attlie rate ofZOOtimes in one secondby the switch. This-produces a train of very'short pulses each havinganunusually fast rise time and each having a length equal't'o or less than the time required for the reed tip 12 to slice through the elevated mercury section It}.

The. switchi is particularly adapted for forming part of'a coa'xiallline: as it hasa substantially uniform crosssection along its. length. This. construction minimizes reflections that might otherwise.v be caused'by an impedance mismatch along the line and is thereby conducive tothe production of. pulses having the desired sharp shape. The pulse shape is further improved. due to the fact that thestructure of the switchv 1. as was explained above is suchthat it produces. no contactchatter during operation of the switch 1. a

What is claimed is: 7

An. electric switch. comprising an. envelope. member. containing at one end" a pool of: mercury, aterrninal having a portion extending outside saide'nvelope and-another portionprojecting inside said. envelope and. sub.- merged in said pool,. a. U-shapedmember. of magnetic material positioned in. said pool and attached to the: terminal portion. therein, said. U-shaped member having. two arms and aninterior bottomportiommeans for. elevating a section of said-mercury above the surface of said. pool with the bottom of. saidsection contiguous with the surface of said pool, said means comprising a bifurcated member of non-magnetic materialhaving'forked .portions,.. said. bifurcated member being mounted on-theinterior bottom portion of said U-shapedmember andbetween the arms thereof, the forked portionsof saidbifurcatedmemher. being so. proportioned as to project above the tops'of the arms of. said. U-shaped member. and. also to. protrude above.- the surface-of said pool while their bottom portions remain submerged in-saidpool of mercury, mag netic means external to said envelope for oppositely, polarizing the arms of said U-shaped member, an armature of magnetic materialmounted abovesaid poolformove- Instead of ccnnecting'the switch terminals 3' and 4- ment of its tip transversely between the forks of said bifurcated member, and electromagnetic means external to said envelope for cyclically changing the polarity of said armature tip, said armature having a length sulficient for the maximum downward extent of travel of its tip to reach only to an intermediate point between the References Cited in the file of this patent UNITED STATES PATENTS George June25, 1957

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