US 2667543 A
Description (OCR text may contain errors)
26, 1954 s. R. SMITH ETAL ELECTRIC RIBBON CABLE Filed April 9, 1951 illllllllll I I I I II a 123456789 nmmmmmn r 1 A B C D E F G H J K L ZHYW ATTORNE YS Patented Jan. 26, 1954 UNITED STATES PATENT OFFICE Claims priority, application GreatBritain May 26, 1950 Thepresent invention relates to electrical wir-. lng arrangements and is more particularly con-. cerned with improvements in so-called ribbon cables which may be used in multiple wiring of selector banks in automatic telephone exchanges.
Selector contact banks of the type described-in United States Patent No. 2,149,632 are widely and successfully employed in conjunction with twomotion selectors in telephone systems. In a bank of -this type the contact members are arranged, in a. suitably insulated and clamped arcuate pileup, the particular bank described being often referred to as, a double bank since each of the 10 levels comprises tworows of 11 contacts, 1. e. 220.contacts are provided. The contact members in each level are appropriately splayed towards the ends formingv the. soldering tags so that the 22 tags. are spaced at equal intervals in an arc to providefor easy accessibility.
In a telephone exchange, a bank multiple for a so-called shelf of twoemction selectors may comprise say 10 selector positions located side by side, and each position may be equipped, for instance, with threebanks of the type mentioned, the banks in. each position being mounted one above the other. By. way of example to provide for- 200 :trairlc outlets, the first 10 pairs of con-, tacts in each. bank level are utilised, one bank in each position being adapted to serve 100 twoe wire speech paths, the second bank another 100 speech paths, and .thethird bank providing ac-. cess to the 2 0. private wires associated with the separate speech paths. The 11th. position contacts which often caterior overflow or like conditions. may be. included in the. multiple as required.
Nowthe most widely employed arrangement for multipling the banks involves the use oftwisted pairs of separately insulated (usually fabric. covered) wires, one wire of a pair being pro ress v y looped Over n ed to s m larly located tags in each position, while the other wire ofthe pair is dealt with in the same m nner t co ne together h a tn r t The lengths of wire extending between ta s in adja ent s ec o positions r ue t formed neatly byhand. Bank multiples manufactured according tothe foregoing method have proved very satisfactory in service but it-w-ill be appreciated that the process of manufacturing is slow: and comparatively costly. It may be mentioned that in such multiples the more or less random displacement of the twists in the conductors serves generally to limit cross-talk and nduc ve. pic r and no dou t the a on' ass st d by the. air Spa in h f pndu ter 2 which is inherent in the arrangement described.
From time to time efiorts have been madetgi simplify and speed up h a r ca on. of 319 multiples and in this respectpre-iormed ribbon cables, for use with suitably arranged bank contact soldering tags have been proDOSQd.
It is, already known to modify banks of the general type hereinbefore described so that the tags are extended and formed to terminate in a vertical plane. Moreover it has been proposed that ribbon cables for use in multiples employing such modified banks shall be provided on the basis of one ribbon cable to serve each of the corresponding bank levels of the selector positions. in a shelf. In such ribbon cables, connecting means such as wire loops are arranged to branch from one edge of the insulated body of the ribbon in positionsappropriate to the soldering tags of the banks. Each ribbon is laid across the contact members of. the corresponding levels of the banks, between the clamped portion and h o e i g ag s t a he bod e of the i bons lie Within the bounds of the soldering. tags. The connecting means branching from the rib bon are directed rearwardly'i. e. in the same direction as the soldering: tags, and are then appropriately interlocked with the tagsfwhereuponsoldering may be effected with great rapidity by immersing the tags of the whole shelf in a solder bath. i V
A ribbon cable for multipling selector banks in the foregoing manner must fulfill certain requirements dimensionally and in its physical and electrical properties. In addition to the needifciits constituent insulate d conductors to retain their positions, the ribbon must be compactand, particularly, thin enough to, be accommodated in the very limited space between the tags of two adjacent levels in a bank. The conductors must be strong, flexible and adequately insulatediso that there is no likelihood of breakdowns or short-circuits developing during the manufacture. or normal handling of the ribbon, or when the ribbon is used under severe climatic conditions such as high humidity and ex t remesfof m e a u In the applicants a plication Serial No. 214,823, filed March. 9, 1951 various methodsof manufacturing ribbon cables, which are intended to meet all the foregoing requirements, are described. Briefly, each of'those'methods isconcerned with the manufacture of ribbon cable for multipling purposes by forming an 'initiallyflat ribbon cable into'what has been termeda flat helix having connectingloops along onjdge, the m tia1 ribbon comprising. a plurality of tartaric tors which are arranged in spaced parallel relationship in one plane within a homogenous mass of thermoplastic insulating material, such as plasticised polyvinyl hloride. Although such a ribbon multipling cable will find many useful applications, it may well be that, if it is employed particularly in the speech path bank multiples of large telephone exchanges, the level of crosstalk will be unacceptable.
The suggestion has been made heretofore, with a view to minimising induced currents in a pair of conductors due to the presence of varying currents in other nearby conductors, that a ribbon cable should incorporate the previously described practice of twisting or transposing the conductors forming a pair with respect to each other. According to this arrangement a twisted pair is formed by transposing the relative positions of two adjacent conductors twice between successive connecting loops, and it therefore follows that the thickness of the ribbon will not be uniform, indeed the body of the ribbon will be three and even four wires thick in places. Moreover there is difilculty in arranging the transpositions formed in the various pairs of conductors to reduce interference due to unbalanced capacitative coupling between them.
The chief object of the present invention therefore is to provide an improved ribbon cable for multipling purposes in which transposing of the conductors is effected to reduce cross-talk and pick-up without increasing the thickness of the cable.
According to one feature of the invention in a ribbon cable suitable for the multipling of contact banks of automatic telephone switches having the conductors arranged in zig-zag formation transposition is effected without increasing the thickness of the cable by arranging that at a transposition point the conductors of a pair do not cross at one edge of the cable and at the other edge of the cable the connecting loops for the contacts cross outside the thickness of the cable so as to bring them in the proper place.
According to another feature of the invention in a transposition arrangement for ribbon cable as used for the multipling of contact banks of automatic telephone switches the transposition plans for the various pairs of conductors in a ribbon cable involve transpositions which are all symmetrical about the middle of the bank multiple run along the switch shelf and are different for adjacent pairs of conductors. In a preferred embodiment of the invention the cable is fabricated from conductors individually covered with thermoplastic material, such as polyvinyl chloride, and during the manufacture of the cable the body of the cable or some part thereof is subjected to pressure across the thickness while heat is also applied so as to effect welding of the insulation on abutting conductors whereby the conductors are subsequently retained in correct relationship.
The invention will be better understood from the following description of one method of carrying it into effect which should be read in conjunction with the accompanying drawings comprising Figs. 1 and 2.
Fig. 1 is a typical transposition diagram for a 22-wire ribbon cable suitable for use in conjunction with a lO-position selector shelf having the before-mentioned modified type of double banks, while Fig. 2 shows a stage in the manufacture of a portion of a ribbon cable.
' Referring to Fig. 1, the 22 conductors are designated I to 22 and are arranged in pairs A, B, C, and so on. The connecting loops would of course be arranged ultimately to branch from the edge of the cable at the selector positions which are referred to as SP! and SPIO. It will be understood that the conductors are arranged in a zig-zag formation across the width of the cable and for convenience the various appearances of the conductors along the other (or back) edge will be referred to as the back folds and are accordingly designated BFI to BFS.
Starting at selector position SPI, the 22 conductors traverse the width of the cable diagonally, and in parallel relationship, to the back fold BFI. At this position, transpositions are effected upon pairs A, C, F, G and J. At the next back fold, BFZ, the conductors in pairs B and H are transposed. A perusal of the diagram shows that transpositions are made as required in accordance with a pre-arranged pattern at intervals along the back edge of the ribbon. Considering particularly the first two pairs of conductors A and B, it will be apparent that the equally spaced transpositions occur at the odd and even numbered back folds respectively. It can be seen from the diagram that in the aggregate the individual wires of pair 13 lie alongside wire I for equal distances, and likewise the wires of the same pair lie alongside wire 2 for an equal distance. Conversely similar considerations apply to the relationship of pair A with regard to wires 3 and 4. Thus in the ideal state, capacity unbalance between these adjoining pairs of conductors, which may of course be employed in separate talking circuits, is substantially elimi nated with a consequent reduction in cross-talk. It will be appreciated that by an extension of the foregoing considerations, the six pairs of conductors A, B, C, D, E and F will be substantially non-interfering with respect to each other. Now the transpositions in each of the remaining pairs of conductors G, H, J, K, and L correspond respectively with those of the beforementioned pairs A, B, C, D and E. Hence although the pairs of conductors in the former group, like those of the latter, are substantially non-interfering with respect to each other, it might be expected that some coupling would occur due to capacity unbalance between corresponding pairs in each group. However the distance between said pairs is sufficient to render this coupling negligible.
Reference will now be made to Fig. 2 which pertains to the layout and manufacture of a ribbon cable in accordance with Fig. 1. However, only six conductors, l to 6, and three selector positions, SPI to SP3, are shown, in order to simplify the description and drawing, and it will be appreciated that a degree of distortion has been introduced insofar as the distances between corresponding connecting loops in the various selector positions are reduced and this results in the spacing of the conductors in their edge to edge runs being exaggerated.
Preferably the cable involves the use of, say, .018 diameter conductors which have been previously insulated with thermoplastic material such as polyvinyl chloride, applied by an extrusion process to give an overall diameter of about .040. Moreover the insulating coverings of the odd and even numbered wires may be distinctively coloured to assist in the subsequent identification of the conductors.
In the manufacture of the ribbon by hand, three groups of pins such as Wl to W6, X] to X9 and; Y1 to Y1 for each selector position of' the ribbon, and a grou of pins ZI to Z! for each backfold position, are fixed in a flat metal base plate. Now. considering the A pair of conductors, and conductor I in particular, this is anchored topin WI-, passed between pins XI and X2; then tgrthejleftof pin Y2, and; below pin Z1 and Z3, and" so on, as indicated by the continuous thick line. Afterwards the partner conductor, A'+.., hih s s o n a e tinuou h nline is anchored to pin' W2, threaded between pinsX3 and Y3, and then for-med round a single pin Z2 and so on. In considering conductors I and 2 together, it is interesting to note that the transposition required at back fold BF'I (vide Fig. 1) is obtained without crossing the conductors. The correct appearance of connecting loops I and 2 at position SP2 is obtained by crossing over the loops outside the body of the ribbon, the cross over serving also to maintain the transposition introduced at BFI. Since no transposition is required at BFZ, the conductors are formed below two pins each i. e. wire 2 below pins ZI and Z2 and wire I below pins Z2 and Z3. Thus at back folds BFZ a transposition does not occur although th wires cross. Again at position SP3 the correct location of the loops is obtained and the relative positions of the conductors in the body of the ribbon is maintained by crossing the loops. The next transposition of the A pair occurs at fold BF3 and this is effected due to conductor 2 passing below pins ZI to Z3, while conductor I passes below pin Z2 only.
Conductors 3 and 4, forming pair B, which are conveniently shown respectively as thick and thin lines broken into alternately long and short dashes, are anchored at pins W3 and WA. and, since no transposition is required at BFI, both conductors pass below two pins each and are crossed over. The conductors then run parallel to position SP2 where the loops are formed but do not cross over since a transposition has not to be catered for. Conductors 3 and 4 are transposed at back fold BF2 by the reviously described method of passing the former below three pins and the latter below the middle pin of the three, the correct order of appearance of the relevant loops at position SP3 being obtained by crossing the loops. The conductors then traverse the ribbon again diagonally to back fold BF3 where no transposition is effected, and accordingly they pass below two pins each. In further applying the layout prescribed by Fig. 1, conductors 5 and B of pair C, shown as thick and thin lines respectively broken into short dashes, are anchored at pins W5 and W6 and it will be noted that transposing of the conductors along the lower edge of the ribbon, together with the arranging of the correct locations of the loops is effected as required after the manner of the methods already described.
It can now readily be seen that by employing the principles described with reference to Fig. 2, a 22-conductor (11 pairs) cable, for use with a ten-position selector shelf, and having transpositions according to Fig. 1 may be formed, and it will be noted that such an arrangement has the advantage that at no point in the cable are more than two conductors encountered in its thickness. By a judicious arrangement of the pins, the conductors may be formed so as to be in abutting relationship in their edge to edge runs across the cable, or to be spaced singly or in groups.
After completion of the weaving or forming of: the: conductors, as described, the body of' the cable, or parts thereof as may be required, is subjected to pressure across its thickness while heat is also applied. Under these circumstances the abutting heated portions of the thermoplastic (polyvinyl chloride) coverings flow and weld together so that, when the ribbon cable islater removed from the base plate, the conductors retain'their positions.
Those portions of the conductors which form theconnecting'means maybestripped by a cutting or scraping orlike operation with or without the application of heat.
Now, if in the formation of a selector multiple, a plurality of ribbons conforming to Fig. 1 are mounted directly one above the other it will be apparent that an appreciable amount of coupling may occur between corresponding pairs in adjoining ribbons. In order to reduce this coupling it will be of advantage to use two types of ribbon in the pile-up alternately, one type being, say that precisely described, and the other havin the pair A transposed like pair D of Fig. 1, pair B like pair E and so on. By this means interfering pairs in adjoining ribbons are so remote as to considerably reduce the possibility of cross-talk.
It will be understood that the method of manufacture of a ribbon cable accordin to the invention is in no way limited to the precise arrangements described. For instance, instead of the manual methods of forming the ribbon, a weaving or forming machine adapted to deal with each of the wires of the cable either singly or collectively may be employed. Further it is not necessary that the ribbon cable be fabricated from thermoplastic covered wires and subjected to heat and pressure as described. Indeed the conductors might well be of the fabric covered type and the conductors could be retained in position in the body of the ribbon by the applica tion of thin adhesive tape to the faces.
1. A ribbon cable suitable for the multipling of contact banks of automatic telephone switches having the conductors arranged in zig-zag formation in which transposition is effected without increasing the thickness of the cable by arranging that at a transposition point the conductors of a pair do not cross at one edge of the cable and at the other edge of the cable the connecting loops for the contacts cross outside the thickness of the cable so as to bring them in the proper place.
2. A ribbon cable suitable for the multipling of contact banks of automatic switches having the conductors arranged in zig-zag formation from edge to edge of the cable and. having connecting loops formed in all the conductors at each successive appearance along one edge in which transposing of the conductors of any pair is effected at an appearance of the conductors at the edge remote from that providing the connecting loops and in such manner that not more than two conductors are included in the thickness of the cable at any point.
3. A ribbon cable as claimed in claim 1 in which transpositions of different conductors are effected according to different plans all of which involve transpositions at points which are symmetrical about the middle of the bank multiple run along the switch shelf and are different for adjacent pairs of conductors.
4. A ribbon cable as claimed in claim 1 in References Cited inthe file of this patent which the eonduotors are individually covered UNITED STATES PATENTS with thermoplastic insulating material and are maintained in correct position due to the Weldin Nugnber Name Date of the insulation by the application of heat and 5 "923775 Barrett 1888 pressure after the forming of the cable. 449,685 Lyon 1891 5. A ribbon cable'as claimed in claim 1 in 504,464 Balsley Sept- 1893 which the conductors are provided with textile 1,000,614 McBerty 1911 insulation and are maintained in proper position OTH R, REF REN by the application of adhesive tape or the like 10 on one or both sides.
SIDNEY REYNELL SMITH. CECIL RHODES.
Abbott, Telephony, Part IV, Fig. 126 (page 245).