Patent GB-1466134-A (GB)
Title: System for the television surveilance of several sectors
IPC: H04N7/18
Filed: 1974-06-07
Abstract: 1466134 Television surveillance THOMSON-CSF AUDIO-VISUEL (TAV) 7 June 1974 [8 June 1973] 25495/74 Heading H4F Relates to television surveillance of several (n) sectors distributed along a path from a single monitoring station C, each sector being equipped with a sector station these stations being numbered 1 to n from the sector station located furthest from the monitoring station. The surveillance is particularly suitable for monitoring road traffic, the video signals from each sector station being sequentially transmitted so that their respective display monitors are sequentially updated in the monitoring station, or if desired any one sector station may be selected for continuous video signal transmission and display. A cable 4 is responsible for transmissions from the monitoring station towards the most distant sector station where, at 2, a cable 5 is connected, this being responsible for the distribution of the primary signals to the different sectors and for their return to the monitoring station as well as for the transmission of signals coming from the various sector stations to the monitoring station. In operation the monitoring station C, by means of a transmitting circuit 6, supplies all the sectors with coded horizontal blanking and vertical blanking signals and, after each coded vertical blanking signal, an address identifying a sector and normally remaining the same at least over three successive fields. A camera at each sector station operates in synchronism with the blanking signals which they receive, and supply a video image signal for a field period each time they receive their address signal. It will be evident that if the sector stations each transmit after receiving their address, the video image signals of a sector can thus be inserted, without overlap, into the active field periods following the vertical blanking intervals characterized by their address, but if one and the same address is emitted for an arbitrary number of fields, the image signals of the corresponding sector station will be inserted into all the active field periods. Each sector station such as station 1 comprises a shift register 12 with 9 + p stages (p being the number of digits in the address signal) followed by a switch 13 arranged in series in the cable 5, a controlled clock 14 shunt supplied from cable 5 and applying pulses at the frequency of the bits incorporated in the coded signals to the shift input 15 of the register, and a system 16 comprising receiver circuits, the camera and the transmission circuits. The system 16 is connected to the (9+p) outputs of the register 12 and to the output of the controlled clock 14. At its output 17, connected to the second input of the switch 13, it produces the video image signals during the active periods. The system 16 at its output 18 delivers a switching signal which is applied to the control input 75 of the switch 13 in order that the latter shall either transmit the output signal from the register 12 in a continuous fashion if the last address signal decoded in the device 16 is not that of the sector 1, or transmit the output signal of the register 12 during the blanking intervals, and the coded image signal delivered by the system 16 of the station during the image scan periods. The monitoring station C is equipped with a receiver circuit 7 connected to the cable 5 and followed by an assembly 8 formed by n image reproducing channels each includng a storage tube and a video display. The circuit 7 decodes the signals which it receives from the cable 5 and supplies all the requisite signals to the assembly 8, namely: at its output 9 the video image signal; at a set of outputs 10 the line and field frequency signals utilized jointly in the n image channels; and at a set of outputs 11 the control signals applied to a single one of the n channels, in particular the switching signals which make it possible to direct the image signal appearing at the output 9, to the appropriate channel. The storage tubes make it possible to maintain the image in the different image channels between the successive reception of video frames from each station. That is, during the first of three fields the storage tube of a channel is erased, during the next two fields the received interlaced video signal is recorded and thereafter it is read-out to maintain the image or the display, the received video being displayed directly during the erase and recording modes.