EP0920035A1 - Data transmission cable - Google Patents

Abstract

A data transmission cable has insulated copper conductors twisted together in pairs or fours inside a multilayer sheath. The cable consists of assemblies of solid copper conductors (3) with insulating sleeves (4), twisted in pairs or fours and enclosed in a multilayer sheath. The insulating sleeves have different relative dielectrical constants, so that the difference in propagation time between the conductors in one assembly and those in another is less than 2ns/100m. The conductors in a single assembly can have insulating sleeves made from materials of the same type but having different relative dielectric constants.

Description

The present invention relates to a data transmission cable. It relates to more particularly such a cable intended to be used in the computer field or in the field of telephony.

European patent EP-B-0.599.672 describes a high signal transmission cable frequency, comprising at least one unit of conductors, each unit comprising at least at least two sets of conductors, such as a quarter of twisted conductors, each conductor being insulated by a first insulating sheath, said unit, or several of said units, being surrounded by a second sheath consisting of a thin envelope extruded in insulating material, located in contact with the conductors of the assembly conductors without the latter being embedded in the sheath which it constitutes, said insulating material having both sufficient rigidity to maintain said conductors in a determined position during handling of said cable and sufficient elasticity to allow these manipulations.

However, to obtain a level of crosstalk compatible with good transmission in a cable comprising at least one unit of at least four conductors twisted under form of sets of conductors which are pairs or quads, the pitch of twists of said sets of conductors are different. The problem for the data transmission is therefore that, each set of conductors having a different electrical length, signals emitted simultaneously at one end of the cable in each of said sets of conductors arrive at the other end of the cable with a time lag. The problem is all the more annoying as the flow rates data transmission are high.

Currently this difference is compensated by active equipment associated with Passive buffer memory equipment. These memories are expensive and will have to have an increasing storage capacity.

So the problem is to overcome the difference in transmission time between the conductors of the same set of conductors and the conductors of a another set of conductors, said sets of conductors being located in a data cable unit. The object of the present invention is to make a data transmission cable that solves the problem, in that it significantly reduces the difference in propagation time between conductors of said sets of conductors, i.e. generally obtaining a such difference in propagation time less than 2 ns / 100m.

The present invention provides for this purpose a data transmission cable comprising at least one unit of at least four conductors twisted in sets of conductors, which are fourths or pairs, each set of conductor being twisted with a different pitch from any other set of conductors and each conductor being insulated by means of an insulating sheath, said unit being enveloped by at least one assembly means, said cable being characterized in that the material used for the insulating sheath of any conductor of a given set of conductors has a relative dielectric constant different from the material used for the sheath insulating any conductor from another set of conductors, so that the difference in propagation time between the conductors of said set of conductors and the conductors of the other set of conductors be less than 2ns / 100m.

A preferred embodiment is such that said unit comprises eight conductors, under in the form of two quartes or four pairs.

Said cable according to the invention is advantageously such that said assembly means includes at least one sheath called unit sheath located in contact with the conductors sets of conductors.

Thus, in the case where the unit is in the form of two quarters of conductors twisted, the material used for the insulating sheath of each conductor of the first quad has a relative dielectric constant different from the material used for the sheath insulating of each conductor of the second quarter.

Thus, in the case where the unit is in the form of four pairs (respectively of two pairs) of twisted conductors, the material used for the insulating sheath of each conductor of the first pair has a different relative dielectric constant of the material used for the insulating sheath of each conductor of each of the three other pairs (respectively from the other pair).

Advantageously, the material used for the insulating sheath of any conductor of a set of conductors of a cable unit according to the invention, chosen from materials having a relative dielectric constant suitable for making the cable according to the invention, a low molecular mobility within it. This molecular mobility due to a more or less high polarity of the dipoles within the material according to the nature of a given material is a known datum, and it is represented by the value of tangent δ. Typically this value is less than approximately 5.10 ^-4 at 100 kHz for a material used for the insulating sheath of a conductor of a set of conductors present in a cable unit according to the invention.

To obtain a cable according to the invention, it is necessary to have materials having different relative dielectric constants, in order to produce the insulating sheath of all the conductors of the same set of conductors in the same material given, the insulating sheath of the conductors of any other set of conductors being made of another material.

The insulating sheath of any conductor of a given set of conductors is therefore made of a given material, different from the insulation materials used for insulating sheaths of conductors of other sets of conductors: each set of conductors twisted according to a given pitch is associated one and only one insulating sheath material uniquely. The materials each making the sheath insulating of all the insulating sheaths of the conductors of a set of conductors given are either different materials, chosen for their dielectric constants different, or materials of the same kind but having a constant different relative dielectric.

By way of example, we can cite the different types of polyethylene materials, which currently make it possible to have a range of relative dielectric constants approximately from 1.6 to 2.3, the higher density polyethylene having a dielectric constant d about 2.3 and the expanded materials such as expanded polyethylene or expanded polypropylene having a relative dielectric constant of the order of about 1.6. On the other hand, the tangent δ of this type of material is typically of the order of 10 ^-7 to 10 ^-6 at 100 kHz. Mention may also be made of expanded materials, synthesized in a manner known to those skilled in the art by the "foam skin" technique. Said expanded materials have a cellular insulation material with a very low dielectric constant, of the order of approximately 1.3 to 1.4, such as cellular polyethylene, said cellular insulation material being surrounded by a layer or " protective polyethylene skin full of higher dielectric constant, of the order of about 2.0, and of a thickness of said layer typically of the order of 50 μm. Finally, we can also cite as examples different fluoropolymers such as PTFE (polytetrafluoroethylene), PCTFE (polychlorotrifluoroethylene), PVDF (polyvinylidene fluoride), PEP (poly (ethylene-propylene) perfluorinated), E.CTFE (ethylene.trichlorofluoroethylene) or ETFE (ethylene - PTFE copolymer), which have relative dielectric constants of the order of about 2 to 2.6 and on average tangent values δ less than about 5.10 ^{- 4} to 100 kHz.

As is known to those skilled in the art, the sets of conductors present in the cable unit according to the invention, having the property of having a constant different dielectric for the sheath of each conductor of a set of conductors given in relation to any conductor from another set of conductors, must have practically the same impedance to be able to use any pair of said cable (alone or from a quarter) in the same subsequent application. It is why a logical consequence of the previous property is that the diameter of the insulating sheath of each conductor wire of a set of conductors of the unit cable according to the invention is different from the diameter of the insulating sheath of each wire of conductor of any other set of conductors of said unit.

According to a first embodiment of the invention, the cable according to the invention comprises a unit of two quarters of conductors, these quarters being grouped inside a unit sheath surrounded by a metal screen, an outer casing being arranged around said unit of two quartes placed side by side. A thread of continuity screen can be installed parallel to the conductors between the unit sheath and the screen.

In a variant of this embodiment, the quarters are simply grouped together the inside of an envelope arranged around said unit of two quartes placed side by side rib, generally made up of a ribbon which acts as a screen. As part of this variant neither unit sheath nor continuity wire is used.

According to a second embodiment of the invention, the cable according to the invention comprises a unit of four pairs of conductors, these pairs being grouped together the inside of a unit sheath surrounded by a metal screen, an outer casing being arranged around said unit of four pairs put side by side as it is known to those skilled in the art. Screen continuity wire can be installed in parallel to the conductors between the unit sheath and the screen.

In a variant of this embodiment, the four pairs are simply grouped inside an envelope arranged around said unit of four pairs placed side by side, generally made up of a ribbon which acts as a screen. In the frame of this variant neither unit sheath nor continuity wire are used.

According to a third embodiment of the invention, the cable according to the invention comprises a unit of two pairs of conductors, these pairs being grouped together inside a unit sheath surrounded by a metal screen, an outer casing being arranged around said unit of two pairs placed side by side. A screen continuity wire can be installed parallel to the conductors between the unit sheath and the screen.

In a variant of this embodiment, the two pairs are simply grouped inside an envelope arranged around said unit of two pairs placed side by side, generally made up of a ribbon which acts as a screen. In the frame of this variant neither unit sheath nor continuity wire are used.

According to another possible embodiment, in the case of the presence of a sheath insulating unit, the cable comprises, in addition to the unit (s) of conductor assemblies (e.g. quads), surrounded by thin insulating unit sheath envelope, other elements, insulating or not, all arranged inside a outer protective envelope, possibly preceded by a metal screen.

Furthermore, to facilitate the stripping of conductors, the possible unit sheath can be split longitudinally over all or part of its length.

Other characteristics and advantages of the present invention will appear in the description which will follow of a particular embodiment of the invention, given as illustrative and in no way limitative.

• la figure 1 est une vue en perspective avec arrachements partiels d'un câble selon l'invention,
• la figure 2 est une vue en coupe dudit câble de la figure 1.

In the following figures:

• FIG. 1 is a perspective view with partial cutaway of a cable according to the invention,
• Figure 2 is a sectional view of said cable of Figure 1.

In these figures, the common elements have the same reference numbers.

FIGS. 1 and 2 show a flat cable 1 according to the invention. Cable 1 has two quarters 2 and 2 '. The fourth 2, respectively 2 ', consists of a twist of four solid copper conductors 3, the conductors each being insulated by a first insulating sheath 4, respectively 4 '.

For the fourth 2, the diameter of the solid conductors 3 is 0.51 mm (± 3 μm), and the diameter of the conductors 3 insulated by means of the sheaths 4 is 1.2 mm. The sheath 4 is made of solid polyethylene with a relative dielectric constant 2.28 and a tangent δ equal to about 2.10 ^-4 at 100 kHz. The quartering pitch is 41.8 mm.

For the fourth 2 ', the diameter of the solid conductors 3 is 0.51 mm (± 3 µm), and the diameter of the conductors 3 insulated by means of the sheaths 4' is 1.15 mm. The sheath 4 ′ is made of expanded polyethylene with a relative dielectric constant 2.26 and a tangent δ equal to approximately 2.10 ^-4 at 100 kHz. The quartering pitch is 33.0 mm.

Quarters 2 and 2 ', arranged side by side, are grouped in a unit of two quartes, referenced 5. The unit 5 is surrounded by an insulating unit sheath 6, located directly in contact with the insulated conductors (3, 4; 3, 4 '). Sheath 6, classic, is consisting of a thin 0.25 to 1 mm thick polyethylene envelope. She can be ribbon or extruded.

A screen 7, in the form of a thin metallic sheet, for example of aluminum-polyester tape lengthwise, is optionally arranged around the sheath 6. This screen serves as a shield to avoid disturbance of the signals carried by the cable by external electromagnetic radiation.

A screen continuity wire 8 is disposed between the sheath 6 and the screen 7, parallel to the quarters 4 and 4 '.

Finally, the unit 5 of the two isolated and shielded quarters is wrapped in an outer support and protection envelope 9 made of PVC, extruded around the assembly. The casing 9 gives the cable 1 an oblong structure of dimensions, approximately equal to 4.3 x 6.5 mm ² .

To facilitate the stripping of the conductors 3 of the cable 1, in particular for the connection of the latter to another cable or to any device, the sheath 6 can be incised longitudinally (see Figure 2), as shown in 10. In addition, the material constituting the sheath 6 is chosen so as not to adhere to the material constituting the sheaths 4 and 4 'of the conductors 3, always in order to facilitate the stripping of these last.

The cable 1 according to the invention can in particular be used in local networks computer, for example to connect the floor distributor and the user outlet.

Example

• une première quarte de quatre conducteurs massifs identiques en cuivre de 0,51 mm chacun isolé à 1,2 mm en polyéthylène massif de constante diélectrique relative 2,28, de pas de quartage de 41,8 mm, et
• une seconde quarte de quatre conducteurs massifs identiques en cuivre de 0,51 mm chacun isolé à 1,15 mm en polyéthylène cellulaire de constante diélectrique relative 2,26, de pas de quartage de 33,0 mm,

les deux quartes étant réunies en parallèle sous une petite gaine de maintien en polyéthylène,
ledit câble possédant en outre un écran qui est un ruban aluminium - polyester en long, et une gaine extérieure oblongue d'environ 4,3 x 6,5 mm².A cable according to the invention as described above and shown in Figures 1 and 2, having:

• a first quarter of four identical solid copper conductors of 0.51 mm each insulated to 1.2 mm of solid polyethylene with a relative dielectric constant 2.28, a quarter pitch of 41.8 mm, and
• a second quarter of four identical solid copper conductors of 0.51 mm each insulated to 1.15 mm of cellular polyethylene with a relative dielectric constant 2.26, with a quarter pitch of 33.0 mm,

the two quartes being joined in parallel under a small polyethylene holding sheath,
said cable further having a screen which is an aluminum-polyester ribbon in length, and an oblong outer sheath of approximately 4.3 x 6.5 mm ² .

The cable thus obtained according to the invention has a difference in propagation time less than 1 ns / 100m.

• une première quarte de quatre conducteurs massifs identiques en cuivre de 0,51 mm chacun isolé à 1,1 mm en polyéthylène cellulaire de constante diélectrique 1,77, de pas de quartage de 41,8 mm, et
• une seconde quarte de quatre conducteurs massifs identiques en cuivre de 0,51 mm chacun isolé à 1,1 mm en polyéthylène cellulaire de constante diélectrique 1,77, de pas de quartage de 33,0 mm,

les deux quartes étant réunies en parallèle sous une petite gaine de maintien en polyéthylène,
ledit câble possédant en outre un écran qui est un ruban aluminium - polyester en long, et une gaine extérieure oblongue d'environ 4,3 x 6,5 mm².By way of comparison, a cable according to the prior art, with a structure close to that of said cable according to the invention but with a different insulation thickness of the conductors compared to the cable shown in FIGS. 1 and 2, has:

• a first quarter of four identical solid copper conductors of 0.51 mm each insulated to 1.1 mm of cellular polyethylene of dielectric constant 1.77, of quarter pitch of 41.8 mm, and
• a second quarter of four identical solid copper conductors of 0.51 mm each insulated to 1.1 mm in cellular polyethylene with a dielectric constant 1.77, with a quarter pitch of 33.0 mm,

the two quartes being joined in parallel under a small polyethylene holding sheath,
said cable further having a screen which is an aluminum-polyester ribbon in length, and an oblong outer sheath of approximately 4.3 x 6.5 mm ² .

The comparative cable has a difference in propagation time of the order of 5 ns / 100m.

Of course, the invention is not limited to the embodiment which has just been described.

Thus, the cable produced according to the invention can be a cable comprising at least one unit of four pairs arranged at the vertices of a square, each pair being twisted and the set of the four pairs being twisted as is known to the man of the job. This embodiment therefore comprises five different twisting steps, but obviously only four steps, or four insulation sheath materials of different conductor, are necessary to achieve the significant decrease in difference propagation time according to the invention.

Furthermore, the cable produced according to the invention can be a cable comprising at least a unit of two pairs next to each other, each pair being twisted and all of the two pairs being twisted as is known to those skilled in the art. This embodiment therefore comprises three different twisting steps, but obviously only two steps, i.e. two different conductor insulation sheath materials, are necessary to achieve the noticeable decrease in time difference of propagation according to the invention.

According to another embodiment, in the case of the presence of a unit sheath insulating, possibly preceded by a metal screen, a cable according to the invention can have, in addition to the unit (s) of conductors surrounded by the unit sheath insulating according to the invention (thin envelope), other elements, insulating or not (such as for example solid conductors), all arranged inside an envelope of protection.

The screen and the outer protective casing are therefore not necessarily arranged directly in contact with the insulating unit sheath according to the invention, in the case of the presence of such an insulating unit sheath, and it is possible that a cable according to the invention does not include a screen and / or no envelope protective exterior.

Alternatively, there is no unit sheath as described above and it is the screen which serves as a sheath for the sets of conductors of said unit.

A cable according to the invention can also have a dual structure (i.e. a structure divided into two units), typically flat or flattened.

The cable according to the invention is not necessarily intended to be used in the IT domain. It can for example be used in telephony.

Claims (11)

Data communication cable comprising at least one unit of at least four conductors twisted into sets of conductors, which are quarter or pairs, each set of conductors being twisted with a pitch different from any other set of conductors and each conductor being insulated by means of an insulating sheath, said unit being surrounded by at least one assembly means,
said cable being characterized in that the material used for the insulating sheath of any conductor of a given set of conductors has a relative dielectric constant different from the material used for the insulating sheath of any conductor of another set of conductors, so the difference in propagation time between the conductors of said set of conductors and the conductors of the other set of conductors is less than 2ns / 100m. Cable according to claim 1 such that said assembly means comprises at least a sheath called unit sheath located in contact with the conductors of the sets of unit conductors. Cable according to one of claims 1 or 2 as the unit is in the form of two pairs of twisted conductors. Cable according to one of claims 1 or 2 as the unit is in the form of two fourths of twisted conductors. Cable according to one of claims 1 or 2 as the unit is in the form of four pairs of twisted conductors. Cable according to one of claims 1 to 5 such that the material used for the insulating sheath of any conductor of a set of conductors of the unit of said cable has a molecular mobility, represented by the tangent value δ, less than 5.10 ^-4 to 100 kHz. Cable according to one of Claims 1 to 6, such as the materials each producing the insulating sheath of all the conductors of a given set of conductors are different materials. Cable according to one of Claims 1 to 6, such as the materials each producing the insulating sheath of all the conductors of a given set of conductors are materials of the same kind but having a relative dielectric constant different. Cable according to one of claims 7 or 8 such that said materials are polyethylene materials. Cable according to one of claims 7 or 8 such that said materials are fluoropolymer materials. Cable according to one of Claims 1 to 10, such as the diameter of the insulating sheath of each conductor wire of a set of conductors from the unit of said cable is different from the diameter of the insulating sheath of each conductor wire from any other set of conductors of said unit.

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