US2599314A

US2599314A - Low capacity switch

Info

Publication number: US2599314A
Application number: US758684A
Authority: US
Inventors: Lloyd J Bobb
Original assignee: Int Electronics Co
Current assignee: Int Electronics Co; INTERNATIONAL ELECTRONICS Co
Priority date: 1947-07-02
Filing date: 1947-07-02
Publication date: 1952-06-03
Anticipated expiration: 1969-06-03

Description

June 3, 1952 055 2,599,314

LOW CAPACITY SWITCH Filed July 2, 1947 2 SHEETS-SHEET 1 INVENTOR M4?- W d iln/M ATTORNEYS June 3, 1952 L. J. BOBB 2,599,314

LOW CAPACITY SWITCH Filed July 2, 1947 2 SHEETS-SHEET2 7? ATTORNEYS Patented June 3, 1952 LOWCAPAOITYfSWITCI I I Lloyd .J'. -.Bobb, ;.,Glcnside, .Pa;,,assign 1m 4 Internatio'nalv Electronics. (lo mpany-,- A Philadelphiag Pa a corporation of; Pennsylvania- 8 'Claims. 1;.

Thisinventi'on:relates t electricalswitchestand more particularly 1 has i to do with electrical switches for use wliereit is essential toreduce the capacity between the" circuits being-switched to a;

Itis frequently necessar-yin electronic work to provide" for 'alternativelycoupling a circuit element such as a magnetic recording head or a speaker microphone to the input and output of a highfgai'n v'acuumtube amplifier; The difference ineriergyievels between the input and output of such amplifiers may be very high. Forexample, in magneticrecording' amplifiers, the ratio of voltagesl at the output and input may be as high as onemillion toone. It will be understood, therefore; that the transfer of even a very slight amount of energy from theoutput circuit to the input circuit will result in oscillations. Even a very. small, amount of capacity between switch contactsjmay result in the transfer of sufficient energy to produce such an-effect.

A principal object of. theinvention is an electricalswitchinwhich the direct capacity between theacti ve and inactive contacts is at a minimum.

Afurther object of the invention is to provide for simultaneous switching of a plurality of circuits ;while retaining different portions of the circuits imelectrostatic isolation from one another.

The invention also contemplates. an electrical switch adapted to massproduction and assembly from a minimum number of simple components.

Howthei foregoingand'other objects are attainedgwill be' mo're' clearlyv understood from the description,hereinbelow" and the drawings, in.

which:

Figure-,1 is a transverseesectional view of a switch constructed'in accordance with the invention, taken alongpthe, line 1-1 in Figure 2;

Fig-uref2is: an axialsection .of the switch of Figures; 1 g. and:

Figure'Bfis aschematic diagramof one application'of the switch of the invention.

Essentially, the switch of the invention takes theformoi a plurality of fixed contacts arranged in a-circle and a link shielded from one another, and comprising a pair of electrically interconnected moving contacts {adapted to engage two of'ftlie fixed. contacts simultaneously, together wi'th a shield surrounding the link, to eliminate capacitycoupling between the moving contacts andltheactivefixed contacts on the one hand and the inactive contacts on the other.

'In;the; embodiment of. the invention illustrated in thegdrawings; the switchcomprises two similar 2:1 1 witch sections. Each; section... as; ma most clearly be seen in Figure 1, comprises four-.-ex;= tern'ally threaded'fixedxcontactpmembers 23113281), 290, and 20d; These:contacts,:lie;in ,a-'; Dlane=.:i

- opposed pairs;xlwithptheraxes oi the -pairs intersecting. The locus of:.the.-'inner ends 'pf the contacts is -a circle: Fixed contact members-% 2%, 26c and-=2 di'are adiustablyif u potted yuiflw ternally threaded; insulating bnshingszzfl, which bushings =in turn are supported'xby an external cylindrical shield ;m'emb'erqi2 5:: Each:.-contact; :26 extendsthrough. external shield-.2 5cto a point just short of the innen surface-inf:-ithe'ashiel'ds- Disposedwithin the circlevisla coiledaspring-ZI mounted within. an."insulatingsblushing 'ii between a pair of: ball contact 11183110613223 zsup ported by i an internal. cylindrical-shield: member 26 which is mounted for: rotation :withinr mem;- ber '25. i As .will .be seen iromsFigure; 1, spring :2! urges ballmembeias' 23' outwardly againstthaiinner surface of external is1eevel25: Advantageously, spring 2i. may bepermanently..ztconnectedtwith contactmembers 23,. as-bysoldering;

Whe'ndnternal; shield 26 isurotated until-spring 2 i and bushing 22 are aligned with a-pair ofzfixed contact members Zihrfor example ivith fixed-con:- tacts 2 Eta and; 2&0, ball members 23 are urged .iinto contact with fixed :contactmembers."2iiaiand '28c, thusestablishing an; electrical circuit through fixed Contact 2 Ga, ball: 23,; spring; 2:! the second ball 23 and fixed contactl2ilci Y In orderv to "ensure centering-of. the 'switcl'u: each fixed contact 26 :is provided at itsjnner: vendwith a depression :21 of spherical contour adaptedlt'o receive .balls 23.. Thus a's :internal sleevet me'm ber 26 is i rotated. ball. members-:23: rideagainst the inner. surface of: external .sleevc za and then snap into depressions121.:.

It will beseen that'in thevpositi'on represented by :Figure' 1,.the electrical .circuit.betweehicnne tact 28a and.contact.20c;istc'ompletely shielded fromboththe inactive contacts z'fihand zod by the internalshield member; 2 6i andaexternal'shield member 25'... The two shieldzmembers. 25 and 26 maybe constructed of anyv conductive material, but preferably of material havinghigh elect zical conductivity, such as, for example,,brass.=

As will also. be seen from Figural, I.have;-pro.- vided individual shields.28 forthe external; leads toeach of the fixed contacts. These external shields may be bonded. to-the fiexible shield 2,9 of the wire 30 by whichgthe switch is connected to other circuit elements.

In Figure 2, I have illustrated two switch,.,sejc- .tions of. .thetypedisclosed in Figure 1 gangedto provide for simultaneous switching of a plurality of circuits. In this figure, internal shield member 26 will be seen to be mounted on a shaft 31, which shaft carries a knob 38. In addition, external shield member 25 is provided with a threaded bushing 39, adapted to penetrate a supporting panel 40 and to be secured in place by a nut 4|. It will also appear from Figure 2 that not only are the contacts of a single switch section shielded from one another as was described above in connection with Figure 1, but that the several contacts in one section are shielded from the contacts in the other section by the portions of the shield members interposed between the two sections. For example, portion 26a of internal shield 26 separates the moving contacts of the two switch sections, and portion 25a of external shield '25 shields the fixed contacts from one another. In addition, individual external shield members 28 serve to electrostatically isolate the external leads from one another.

All of the shield members are in contact with one another, and, when the switch is installed, are connected to ground, for example, through panel 40. Thus, a grounded conducting element is interposed between each contact and every other contact, eliminating direct capacity between the various circuits connected to the switch. Of course, there is capacity between each contact and ground, but since this capacity is not common to any two circuits, no coupling between the circuits can take place.

The problem of capacitive coupling between the input and output terminals of a amplifier is particularly acute in magnetic recording systems, and accordingly, I have illustrated in Figure 3 the application of the invention to a magnetic recording system, although it is to be understood that similar problems arise in other types of circuit and that the invention is applicable to any situation in which it is desired to eliminate capactive coupling between the several circuits to be switched. Included in Figure 3 are an amplifier 32, a speaker-microphone 33, a magnetic recording-reproducing head 34, and a switch of the type illustrated in Figures 1 and 2, comprising a first section 35 and a second section 36. As will be noted from the drawing, one terminal of each of the input and output circuits and one terminal of the speaker-microphone and magnetic recording head is grounded. In addition, I have indicated that the metal parts of the switch sections are also grounded.

In this circuit, the high side of the amplifier input is connected to terminals and d of switch section 35, while the high side of the amplifier output is connected to contacts b and c of switch section 36. The speaker-microphone is connected to contact a of section 35 and also to contact 11 of section 36. Finally, recordingreproducing head 34 is connected to contact b of section 35 and to contact a of section 36. It will be seen, therefore, that when the switch is adjusted to the position in which the coiled spring in each switch section is vertical, as is illustrated in the figure, the speaker-microphone 33 will be connected to the amplifier input through contacts a and c of section 35, and that recordingreproducing head 34 will be connected to the amplifier output through contacts a and c of section 36. It will also be seen that since the amplifier output is connected through switch section 36 to contact a, the amplifier output voltage will appear between ground and contact I) of section 35. If, therefore, appreciable capacity existed between contact I) of section 35 and either contact a, c, d, or the coiled spring of section 35, energy would be transferred from the amplifier output to the amplifier input. But because a large portion of the grounded internal shield member of the switch is interposed between contact I) and all the other contacts, no such capacity can exist and no energy transfer can occur.

It will be understood that while I have illustrated in Figure 2 a switch comprising two sections, a larger number of sections may be incorporated in a single switch, all of which can be controlled by the same knob.

Thus, according to the invention, any pair of contacts may be interconnected in a circuit which is electrostatically isolated from the contacts which are temporarily out of the circuit.

In addition, the invention provides for a toggling or self-centering action by virtue of the cooperation of the ball contacts with the depressions in the fixed contacts.

Furthermore, the switch of the invention is admirably suited to mass production techniques, since the number of parts is small and all are adapted to simple fabrication and assembly.

Iclaim:

1. An electrical switch comprising at least three fixed contacts externally tangent to a circle and disposed at equal angular distances therearound, a connecting link within the circle and in the plane thereof comprising two electrically interconnected contacts capable of internal tangency to the said circle and adapted to selectively engage two of the fixed contacts upon rotation of the link about the center of the circle, said rotatable contacts being angularly spaced from one another by an angle equal to the angle separating two of said fixed contacts, a grounded conductive shield surrounding said link and movable therewith, said shield being constructed and arranged to shield the link from any fixed contact not in engagement with the link, a second grounded conductive shield of cylindrical section whose inside diameter is less than the diameter of said circle, said second shield being pierced by apertures aligned with said fixed contact and adapted to be penetrated by said interconnected contacts, and dielectric means adapted to guide said interconnected contacts from a position of engagement with said second shield to a position of engagement with said fixed contacts.

2. A switch comprising a rotatable cylindrical electrically conductive shield element, fixed contact elements radially outwardly displaced from said shield element and angularly displaced from one another in the same radial plane, and electrically interconnected contact means physically carried by said shield and being angularly displaced from one another in the same radial plane, said interconnected contacts being insulated from the shield and being outwardly extendible from the shield to selectively interconnect a pair of fixed contacts to thereby make an electrical connection between said pair of fixed contacts.

3. An electrical switch comprising an external shielding sleeve penetrated by at least three apertures lying in the same radial plane, an insulating bushing extending to the inner surface of the sleeve in each aperture, a fixed contact extending to the inner end of each bushing, an internal cylindrical sleeve concentric with the external sleeve and mounted for rotation therein,

an insulating bushing mounted in a transverse bore through said internal shield in the radial plane of said apertures, a spring Within said lastmentioned bushing, a contact member at each end of said spring within said bushing, said contact members being outwardly urged against the inner surface of said sleeve by said spring, and a shaft for rotating said internal shield to bring said contact members into engagement with two of said fixed contacts and thereby establish a circuit through said spring between said two fixed contacts, which circuit is shielded from the fixed contact not engaged by said contact members.

4. A construction in accordance with claim 3 in which said first-mentioned bushing is internally threaded and said fixed contact member is externally threaded to provide for axial adjustment of the contact in the bushing.

5. A construction in accordance with claim 3 in which the spring and contact members comprise a coiled spring and a pair of metal spheres.

6. A construction in accordance with claim 5 and further including a depression in the inner end of each fixed contact member adapted to provide a toggling action in cooperation with the said metal spheres.

7. An electrical switch comprising an external shielding sleeve penetrated by at least three apertures lying in the same radial plane, a conductor insulated from the sleeve in each aperture extending radially inwardly to a point just short of the inner surface of the sleeve, dielectric means in the aperture, an internal conductive cylinder concentric with the external sleeve and mounted for rotation therein, an insulating bushing mounted in a transverse bore through said cylinder in the radial plane of said apertures, a spring within said bushing, a movable contact member at each end of said bushing, said contact members being outwardly urged against the inner surface of said sleeve by said spring, and means for rotating said cylinder to bring said contact members into alignment with said apertures, said dielectric means being arranged to support said contact members in their paths of movement across said apertures between said internal surface and said conductors.

8. An electrical switch comprising an external shielding sleeve penetrated by at least three apertures, a conductor insulated from the sleeve in each aperture extending radially inwardly to a point just short of the inner surface of the sleeve, a pair of movable contact members within said sleeve, means between said contact members urging the said members against the inside surface of said sleeve, means for rotating said contact members into positions of alignment with said apertures, and dielectric means arranged to support said contact members in their paths of movement between said internal surface and said conductors.

LLOYD J. 30133.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,201,881 Bryant May 21, 1940 2,344,780 Kram Mar. 21, 1944 2,360,219 Goddard Oct. 10, 1944 2,425,010 Smith Aug. 5, 1947