US 2259234 A
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Oct. 14, 1941. w vQ 2,259,234
SHIELDED ELECTRICAL DEVICE Filed Jan. 10, 1939 a b 0 /d INVENTOR W/LLY V207 BY ATTORN EY Patented Oct. 14, 1941 SHIELDED ELECTRICAL DEVICE Willy Voigt, Berlin, Germany, assignor to Telei'unken Gesellschaft fur Drahtlose Telegraphic mit beschrankter Haftung, Berlin, Germany, a
corporation of Germany Application January 10, 1939, Serial No. 250,183 In Germany January 10, 1938 1 Claim.
In the operation of electrical devices and arrangements, more particularly those used in the communication arts, it is imperative and necessary to safeguard some circuit elements or even entire assemblies of devices, from the disturbing action of extraneous electrical or magnetic fields in order to insure satisfactory operation.
A simple and often used method and means is to entirely enclose, metallically such parts as require-protection as stated, and to ground the said shield or can or to connect it with zero potential. Shielding means of this kind are known as -cans" when used for coils, tubes, and rotary condensers in radio apparatus. Unfortunately, this safeguarding means, even where closed metallio shields are dealt with, proves often not quite adequate for the reason that in most cases at least one and often more openings must be provided in order to bring current supply leads into-the interior of the shielding enclosure.
These leads, however, are liable to introduce very undesirablestray and disturbing currents into the interior of the shielding can. It has been on this ground that the leads outside the shielding can have been provided with stray eliminator means by connecting the same by Way of condensers, for instance, with the potential of the shielding can, so that the stray frequencies are given a chance to leak away or be grounded.
However, it has been ascertained that even this arrangement is insufficient to maintain the shielded electrical apparatus or device under conditions perfectly free from interference and disturbing actions. The primary reason of this condition seems to be that the portion of the conductor forming the lead up to the condenser terminal and carrying disturbing potentials, in turn, induces disturbing voltages in the portion of the conductor in the rear of the condenser. Another-reason for this condition is that the conductors themselves present a certain potential to the shielding can thus requiring the insertion of insulation between the metallic conductor of the lead and the casing. The opening which is necessary for the lead-in wire andthe insulation material presents a sizable gap through which stray field lines are able to enter the interior of the shielding can. These drawbacks are particularly serious in systems operating at ultra high frequencies.
In accordance with the present invention, the difliculties noted above are overcome by connecting each conductor brought into the shielding can, directly at the point of entry into the shielded range, by way of a leak condenser, with the shield. In the first place this createsconditions so that for the disturbing frequencies a-leak path is provided as already known in the art. However, over and above this feature the portion of conductor carrying disturbing currents is. :no longer able to act inductivelyupon the portion of conductor from which disturbing actions have been eliminated inasmuch as this portion, figured from the point where the condenser is connected, is located inside the shielding can so that it is safeguarded from these effects- This is thespecial feature of the invention,;thereby eliminating a major disadvantage of the shielding means heretofore used. .j I 1 If, moreover, the condenser is arranged symmetrically in relation to themetallic conductor of the line, say, concentrically or co-axially, then the faulty place, due in the past to therequired insulation of the conductor, is:fil1ed up by the closely adjacent coats of the condenser with the result that no stray lines are able to enter into the shielding can or enclosure. j w 5 In order to create a very'simple ,andsuitable arrangement in the sense of this invention,,one coat of the leak or arrester condenser which is to be united with the shield wall, is connected with the metallic container of the condenser which, in turn, may be screwed fast, for instance, at the inlet of the shielding can or preferably connected therewith by soldering in order that, at the same time the shortest possible path may be provided for the stray frequencies.
It is also possible to mount the stray eliminating condenser outside the shielding can and to surround the portion of conductor brought away from the condenser with a metallic shield or sheath being conductively connected with the shielding can.
The arrester or lead-in condenser may be of the folded or rolled (wrapper) type inhering only a low amount of inductance. For instance, a preferred form of such condenser is built in the shape of a hollow wrapper, with the current carrying conductor being brought through the hollow space therein. In a modified form of construction the coat to be united with the conductor could at the same time partly replace the current supply lead so that the lead would be brought from the outside to the condenser fitted into the shielding wall and continued inside.
The drawing shows a schematic representation of the electrical device which is shielded from disturbing extraneous action according to the invention.
Referring to Fig. 1, a comprises an electrical device which is confined within a shielding housing or can b. The said device is connected by way of the current-carrying leads c1, 02 with a source of current or generator 11 mounted outside shielding housing. At the point where the line 01 is brought in across the wall of the shielding can b, there is mounted a leak or arrester condenser e according to the invention. The metal shell of condenser e is directly connected to the shielding can b and to one electrode of the condenser. The other electrode of the condenser is united with the line 01. The line portion 01 which still has stray potential will then no longer be able to produce an inductive action on the conductor portion 02 because of the shielding effect of b, inasmuch as at the lead-in point stray currents are into thefinterior of the shielding can along the line, inasmuch as the insulation space between the lead-in conductor and the shielding can Wall is traversed or filled by the metallic coats of the condenser. Also in this figure c1 denotes the con duct or part subject to stray action, and 02 the conductor part free from stray potential, while 1 represents the metallic sheath of the condenser e.
An axial cross section of another exemplified embodiment ofsuch a lead-in condenser is shown in Fig. 3, with the insulation layersbetween the coats being omitted. In Figure 3, g and h are two metal foils which are wrapped up conjointly as known in the art; Foil g has greater width than foil it so that it protrudes at both ends of the wrapped structure. The projecting turns are interconnected by a layer of metal applied thereon by a spray method, orfby soldering, and they form, on the oneh'and, the terminal 2' for'the line conductor 01, and, upon the other hand, the terminal k for the line conductor 02. In other words, the coat-g, inside the lead-in takes-care of the conduction of thecurrent The foil h which is in capacitive coupling relationship therewith is and discussed concern a single lead, it will be understood that the same idea is just as readily applicable, in a similar way, to any line or lead brought into a shielding can or enclosure. It is also possible to combine several lead-in condensers for several lines within one and the same casing.
' i I claim:
In an electrical circuit including a shielded electrical element, a conductor passing through an opening formed in the shield and adapted'to connect the electrical element to means external the shield, a metallic sleeve member fitted snugly into said opening and conductively' connectedto the shield, a; condenser having a' pair of electrodes inserted Within said sleeve member, means conductively conneotingone electrode of the'cbndenser to the sleeve member, the other electrode of the condenser forming a portion of said 'con ductor through'which the shielded element'is' connected to the means external the shield, said condenser being of the rolled type andarranged so that both edges of the electrodewhich forms a portion of the conductor extend an appreciable distance beyond the corresponding edges ofthe first named electrode of the condenser, a cap-like device ccnductively connected to the shielded element, means including said cap-like device for connecting together the extended edges at one end of said other electrode, a second cap-like device for connecting the extended edges at the other end of said other electrode together, and a conductor for connecting said second cap-likede-l vice to the means external the shield.