GB2188818A

GB2188818A - Improvements relating to data transmission systems

Info

Publication number: GB2188818A
Application number: GB08608450A
Authority: GB
Inventors: Stanley Beddoe
Original assignee: Plessey Co Ltd
Current assignee: Plessey Co Ltd
Priority date: 1986-04-07
Filing date: 1986-04-07
Publication date: 1987-10-07
Also published as: FR2596903A1; GB8608450D0; DE3711602A1; GB2188818B

Description

1 GB 2 188 818 A 1

SPECIFICATION

Improvements relating to data transmission systems h 15 This invention relates to data transmission systems and relates more specifically to data transmission systems facilitating the operation of power controllers at remote locations over data transmission links.

In accordance with the present invention there is provided a data transmission system including at least one data transmission link extending between remotely located controlling and controlled stations, said data link comprising isolating transformers at the respective stations and a pair of conductors, preferably twisted, extending between said stations, in which a direct current or relatively low frequency a.c. power circuit is provided for operating a remote power controller at one or more controlled stations from the controlling station in order to connect a main power supply to data decoding equipment and to enable the transmission of status signals to be made to the controlling station and in which said power circuit comprises parallel paths through the pair of conductors via centre tappings on windings of the respective isolating transformers and a conductive screen for said conductors.

By way of example the present invention will now be described with reference to the accompanying 90 drawings in which:

Figure 1 shows a conventional data transmission link between controlling and controlled remote stations; Figure 2 shows the data transmission link of Figure 1 adapted in accordance with the invention to provide power over the data link for operating a remote power controller; Figure 3 shows a multiple station datalpower link of the kind shown in Figure 2; and, Figure 4 shows a datald.c. power link according to 100 the invention.

Referring to Figure 1 of the drawings there is shown a data link for the transmission of bi-phase encoded data between remote controlling and controlled stations A and B. The data link comprises 105 an earth screened pair of twisted conductors 1 and 2 which are a.c. coupled to the stations A and B through respective d.c. isolating transformers 3 and 4.

In Figure 2 low frequency low power is supplied from controlling station A to remote controlled station B for operating a power controller 8 at station B over a power supply circuit i - ncluding-- centre tapping points on windings of transformers 3 and 4, the pair of conductors 1 and 2, the earth screen 5 of the conductors 1 and 2 and power transformers 6 and 7 at the respective stations A and B. The frequency of the a.c. power supplied for which may be between 25 and 100 kc's. As will readily be appreciated from Figure 2, the power current in the power supply circuit is split equally between the twisted conductors 1 and 2 thereby showing high rejection of the power signal from data being transmitted over the data link.

Figure 3 shows an arrangement similar to that of Figure 2 but including additional remote controlled stations C and D coupled into the data link and the low frequency power supply circuit for the operation of power controllers at the stations C and D as well as at station B. Figure 4 shows a combined data link and power supply circuit for supplying d.c. power from station A to station B over the twisted pair conductors in parallel and including the earth screen of the data conductors.

The power controller 8 at the remote station B or stations B, C and D, as the case may be, may comprise solid-state switching devices and serves to connect a main power supply MS to data decoding equipment DEC at the station in readiness for the reception of coded data to be transmitted over the data link from station A and to initiate the transmission of status signals to the latter station over the data linkto provide an indication as to whether the remote station B or stations B, C and D are able to receive transmitted data.

As will be appreciated f rom the foregoing the power controller is remotely operated by low power received over the data link conductors and the power controller only needs to access one pole of the main power supply thereby avoiding the risk of an internal power short-circuit caused by the power controller, and providing good electrical integrity.

Claims

1. A data transmission system including at least one data transmission link extending between remotely located controlling and controlled stations, said data link comprising isolating transformers at the respective stations and a pair of conductors extending between said stations, in which a direct current or relatively low frequency a.c. power circuit is provided for operating a remote power controller at one or more controlled stations from the controlling station in order to connect a main power supply to data decoding equipment and to enable the transmission of station status signals to take place, and in which said power circuit comprises parallel paths over the pair of conductors via centre tappings on windings of the respective isolating -- -- and a conductive screen for said conductors.

2. A data transmission system as claimed in claim 1, in which the data link comprises a twisted pair of conductors.

3. A data transmission system substantially as hereinbefore described with reference to the operating the power controller 8 at station B maybe 120 accompanying drawings. up to about 115 of the frequency of the encoded data Printed for Her Majesty's Stationery Office by Courier Press, Leamington Spa, 10187. Demand No. 8991685. Published by the Patent Office, 25 Southampton Buildings, London, WC2A lAY, from which copies may be obtained.