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(11) | EP 0 422 306 B1 |
| (12) | EUROPEAN PATENT SPECIFICATION |
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| (54) |
Communication cable Nachrichtenkabel Câble de communication |
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| Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention). |
COMMUNICATION CABLE
[0001] The present invention relates to a thin communication cable which is non-sensitive to moisture from an electrical point of view. A communication cable is especially intended for use in frequencies up to and including the MHz-region. The cable is provided with at least two electric conductors and a surrounding sheath.
[0002] It has been shown that a conventional field thin cable including one, two, or more, pairs of insulated communication wires intended for use at frequencies up to and including the MHz-region, with surrounding sheath, can get an electric line attenuation increase of more than 100% at for instance drizzle at the frequency 1.024 MHz which is considerably more than previously used frequencies. The purpose of the invention is therefore in the first place to provide a communication cable, the electric line attenuation of which holds a low and continuous level also when the cable is subjected to moisture or varying external environment with respect to the weather conditions when using one and the same frequency. This is provided in connection with a communication cable of small diameter of the kind mentioned in the introductory portion first of all thereby that the sheath is composed of three different, mutually combined layers - an internal layer, an external layer and an intermediate layer - and that the intermediate layer consists of a semiconductor material. Said electrical line attenuation can be of the magnitude ≦ 14 dB/km at 1.024 MHz.
[0003] Further advantages and characterizing features concerning the new communication cable are apparent from the following description and from the claims.
[0004] The Fig. shown on the enclosed drawing discloses a section of a communication cable which is formed according to the principles of the invention.
[0005] The communication cable 10 in said Fig. is a so-called two-wire-cable but the invention can, of course, be applicable to a cable with two or more pairs of wires. The communication cable comprises two similar separate electric conductors 12, each consisting of a polyethylene insulated tinned copper wire 14. Moreover, the cable also comprises two tension relieve elements 16, which in this case each consists of a polyethylene insulated stainless steel wire 18. The two insulated conductors 12 and the two insulated steel wires 16 are twisted to a compact quad in a manner known per se. The wires 16 and the conductors 12 are surrounded by a sheath which has been fill extruded around the whole quad.
[0006] As is apparent from the Fig. of the drawing the sheath is composed of three different mutually combined layers. The layers consist of plastic, preferably polyethylene. The internal layer 20 and the external layer 22 are non-conducting but the intermediate layer 24 is semi-conducting.
[0007] The assembly has been made by melting the three layers in one single moment but, of course, the use of glue or some other assembly method may be imagined.
[0008] The internal layer 20 of polyethylene can have a low density, whilst the external layer 22 shall consist of a durable plastic with a high density or another durable plastic, for instance polyamide. The intermediate layer 24 should have a volume resistivity suitable for the line attenuation level, preferably of the magnitude 10²Ωcm, at at temperature of 20°. For the purpose intended it is suitable that the internal layer 20 is between four and six times thicker than the intermediate layer 24.
1. A thin communication cable (10), including one, two, or more, pairs of insulated communication
wires for use at frequencies up to and including the MHz-region, with surrounding
sheath (20,22,24) characterized in that the sheath is composed of three different
mutually combined layers - one internal insulating layer (20), one external insulating
layer (22) and one intermediate layer (24) - and in that the intermediate layer (24)
consists of a semiconductor material, so that the cable, as for electrical signal
transmission, is non-sensitive to moisture.
2. Communication cable according to claim 1, characterized in that the layers (20, 22,
24) consist of plastic.
3. Communication cable according to claim 1 or 2, characterized that the three layers
(20,22,24) are joined by melting at extrusion in one single step.
4. Communication cable according to any of claims 1-3, characterized in that the internal
layer (20) consists of polyethylene with a low density, that the external layer (23)
consists of polyethylene with a high density or of polyamide and that the intermediate
layer (24) consists of semiconductive polyethylene.
5. Communication cable according to claim 4, characterized in that the volume resistivity
of the intermediate layer (24) is of the magnitude 10²Ω cm.
6. Communication cable according to any of claims 1-5, characterized in that the internal
layer (20) is between 4 and 6 times the thickness of the intermediate layer (24).
7. Communication cable according to claim 2, characterized in that the layers (20, 22,
24) consist of polyethylene.
1. Dünnes Nachrichtenkabel (10) mit einem, zwei oder mehr Paaren von isolierten Nachrichtendrähten
für den Gebrauch bei Frequenzen bis einschließlich dem MHz-Bereich mit einem umgebenden
Mantel (20, 22, 24), dadurch gekennzeichnet, daß der Mantel aus drei verschiedenen
gegenseitig kombinierten Schichten - einer inneren isolierenden Schicht (20), einer
äußeren isolierenden Schicht (22) und einer Zwischenschicht (24) - besteht und daß
die Zwischenschicht (24) aus Halbleitermaterial besteht, so daß das Kabel für elektrische
Signalübertragung unempfindlich gegen Feuchtigkeit ist.
2. Nachrichtenkabel nach Anspruch 1, dadurch gekennzeichnet, daß die drei Schichten (20,
22, 24) aus Plastik bestehen.
3. Nachrichtenkabel nach Anspruch 1 oder 2, dadurch gekennzeichnet, daß die drei Schichten
(20, 22, 24) durch Extrusion in einem einzigen Schritt zusammen geschmolzen sind.
4. Nachrichtenkabel nach einem der Ansprüche 1-3, dadurch gekennzeichnet, daß die innere
Schicht (20) aus Polyethylen geringer Dichte besteht, daß die äußere Schicht (22)
aus Polyethylen hoher Dichte oder aus Polyamid und daß die Zwischenschicht (24) aus
halbleitendem Polyethylen besteht.
5. Nachrichtenkabel nach Anspruch 4, dadurch gekennzeichnet, daß der Volumenwiderstand
der Zwischenschicht (24) den Wert 102 L cm hat.
6. Nachrichtenkabel nach einem der Ansprüche 1-5, dadurch gekennzeichnet, daß die innere
Schicht (20) zwischen 4 und 6 mal die Dicke der Zwischenschicht (24) aufweist.
7. Nachrichtenkabel nach Anspruch 2, dadurch gekennzeichnet, daß die Schichten (20, 22,
24) aus Polyethylen bestehen.
1. Fin câble de télécommunication (10), comportant une, deux, ou davantage, paires de
conducteurs de télécommunication isolées, pour emploi à des fréquences allant jusqu'à
et y compris la bande des MHz, comportant une gaine (20, 22, 24) qui l'entoure, caractérisé
par le fait que la gaine est composée de trois couches différentes, mutuellement combinées
- une couche intérieure isolante (20), une couche extérieure isolante (22) et une
couche intermédiaire (24) - et que la couche intermédiaire (24) est constituée d'un
matériau semi-conducteur, de sorte que le câble, en tant que câble de transmission
de signaux électriques, n'est pas sensible à l'humidité.
2. Câble de télécommunication selon la revendication 1, caractérisé par le fait que les
couches (20, 22, 24) sont constituées de plastique.
3. Câble de télécommunication selon la revendication 1 ou 2, caractérisé par le fait
que les trois couches (20, 22, 24) sont réunies par fusion à l'extrusion en une seule
étape.
4. Câble de télécommunication selon l'une quelconque des revendications 1-3, caractérisé
par le fait que la couche intérieure (20) est constituée de polyéthylène basse densité,
que la couche extérieure (23) est constituée de polyéthylène haute densité ou de polyamide
et que la couche intermédiaire (24) est constituée de polyéthylène semi-conducteur.
5. Câble de télécommunication selon la revendication 4, caractérisé par le fait que la
résistivité volumique de la couche intermédiaire (24) est de l'ordre de grandeur de
10² Ω.cm.
6. Câble de télécommunication selon l'une quelconque des revendications 1-5 caractérisé
par le fait que l'épaisseur de la couche intérieure (20) vaut entre 4 et 6 fois l'épaisseur
de la couche intermédiaire (24).
7. Câble de télécommunication selon la revendication 2, caractérisé par le fait que les
couches (20, 22, 24) sont constituées de polyéthylène.