GB2049262A

GB2049262A - Coaxial cable and method of using it

Info

Publication number: GB2049262A
Application number: GB7916683A
Authority: GB
Original assignee: Ward and Goldstone Ltd
Current assignee: Volex PLC
Priority date: 1979-05-14
Filing date: 1979-05-14
Publication date: 1980-12-17
Also published as: GB2049262B

Abstract

A coaxial cable comprises a central conductor 1, an insulating sheath 2, a plurality of strands 3 of an electrically conductive material laid side by side along the sheath 2 parallel to the central conductor 1 and an insulating cover 4. In use, power is supplied to a system through the strands 3, while information for the system is supplied down the central conductor 1. The strands act as a screen inhibiting corruption of the information signals flowing along the central conductor and the radiation of interference from the central conductor itself. <IMAGE>

Description

SPECIFICATION Coaxial cable and method of using it The present invention relates to a coaxial cable.

The cable is particularly, but not exclusively, intended for use in the multiplex information handling and transmission system forming the subject of co-pending application 9493/78.

According to one aspect of the present invention, there is provided a coaxial cable comprising a central element adapted in use to carry information signals therealong and a coaxial surrounding tubular screen adapted, in use, to carry electrical power therealong, the screen consisting of parallel strands of conductive material laid side by side and displaced from the central element.

According to another aspect of the present invention there is provided a method of supplying power and information to a system in which the power for the system is supplied through the screen of a coaxial cable and the information is supplied down the central conductor of the cable.

In order that the invention may be more clearly understood, one embodiment thereof will now be described, by way of example, with reference to the accompanying drawings in which, Figure 1 shows a section of coaxial cable and Figure 2 shows a coaxial cable in use in a multiplex information handling system.

Referring to Fig. 1, the cable comprises a single central conductor 1 surrounded by a sheath 2 of electrically insulating polyvinyl chloride. Laid on the sheath 2 parallel to the central conductor 1 are a plurality of copper strands 3. The strands 3 contact each other to effectively form a conductor of a tubular section. The cable is completed by a further sheath 4 of polyvinyl chloride.

The cable is particularly suited to the provision of d.c. or low frequency (less than 1 MHz where skin effect is negligible) a.c. power.

The construction provides a higher surface area to conductor volume per unit length than would be achieved if the central axial dielectric or insulator were to have zero cross sectional area. The benefit from this increased ratio may be realised in different ways, e.g.: 1) Equal amounts of copper may provide a greater power capacity in this construc tion.

2) Equal power capacity may be realised in this construction with a smaller quantity of copper and provides an appropriate overall decrease in cost and weight even though this is offset slightly by the cost and weight of the increased quantity of outer insulation and the inclusion of the central dielectric or insulator.

This construction also has considerable power rating advantages over "cottage loaf" constructions where the signal conductor is lashed or fastened to the side of the power conductor.

Fig. 2 shows one use to which the cable of Fig. 1 may be put. This Fig. 2 is a diagrammatic perspective view of a local processing unit for a multiplex information handling system of the type described in co-pending application No. 9493/78. The unit has a plurality of inputs 51, a plurality of outputs 52, an input socket 53 for a combined signal and power bus 54 and an output socket 55 for the bus 54 which may be a coaxial cable of the type shown in Fig. 1. The inputs 51, including inputs 51A from switches and analogue sensors, lead to and the outputs 52 lead from circuitry contained in a housing 56 having apertures lugs 57 for connecting it to a convenient support.

The system is intended for a vehicle in particular the relatively small mass produced family saloon. It will replace the present con ventional wiring harness which is becoming increasingly complex, difficult to install and expensive. The combined signal and power bus can be taken simply round the vehicle in a similar fashion to a ring main and local processing unit arranged on it at appropriate positions. The combination of signal and power lines in a signal bus has other advantages. The bus comprises concentrically arranged inner and outer conductors 54A and 54B. The outer conductor, which constitutes the power line, contains a substantial amount of copper which ensures good screening for the inner conductor which constitutes the signal line.This screening effect will minimise the tendency to pick-up voltage spikes on the signal bus from electrical equipment in the vehicle. Also, the screening effect will minimise the interference caused to radio reception in the vehicle from pulses present on the signal bus. Further, the co-axial arrangement is convenient for a moulded plug, and socket connection to each l.p.u., where the large area provided by the outer contact will carry the high current.

The input and output sockets 53 and 55 of each l.p.u. are coaxially arranged. Co-axial "Tee" junctions can be provided as shown in Fig. 2 at 59 to give total flexibility to the wiring of the bus which may form loops or rings with spurs if required. This will enable the current requirement to different loads to be balanced, such that very substantial current capacity of the co-axial outer conductor 54B is avoided. The co-axial cable need not be flexible and the expensive use of braids is not required. The local processing units are spaced along the combined power and signal bus at suitable intervals determined by the load and switch requirements of the vehicle in which the system is installed.

Claims

A A coaxial cable comprising a central element adapted in use to carry information signals therealong and a coaxial surrounding tubular screen adapted, in use, to carry elec trical power therealong, the screen consisting of parallel strands of conductive material laid side by side and displaced from the central element.
2. A coaxial cable as claimed in claim 1, in which the central element and the tubular screen are separated by a tubular insulator or dielectric.
3. A coaxial cable as claimed in claim 1 or 2 in which the tubular screen is covered by a tubular insulator.
4. A coaxial cable as claimed in claim 1 or 2, in which the or each tubular insulator is of polyvinyl chloride.
5. A coaxial cable as claimed in any of claims 1 to 4, in which the central element is a fibre optic.
6. A coaxial cable substantially as hereinbefore described with reference to Fig. 1 or Fig. 2 of the accompanying drawings.
7. A method of supplying power and information to a system in which the power for the system is supplied through the screen of a coaxial cable and the information is supplied down the central conductor of the cable.
8. A method of supplying power and information to a system substantially as hereinbefore described with reference to the accompanying drawings.