GB2082869A - Closed-Circuit Television Surveillance System - Google Patents

Abstract

Television surveillance system comprising a plurality of television cameras CC1, CC2, CC3 which transmit output signals back to one or more monitors MM 1, MM2 which include picture displays. Coaxial cables LL1, LL2, corresponding in number to the number of monitors, extend between the monitors and the cameras via switch arrangements S1A, S1B; S2A, S2B; S3A, S3B. The control units CU1, CU2 send out address signals to the function control units FC1, FC2 etc and provide for the output signals from the cameras to be supplied selectively to the monitors. The system eliminates the need for one cable for each camera and has only as many cables as monitors. Each cable routing is in the form of a ring so that should the ring be broken or severed signals may still be returned to the monitors. <IMAGE>

Description

SPECIFICATION Closed-circuit Television Surveillance System This invention concerns closed-circuit television surveillance systems.

In comprehensive security installations, closedcircuit television systems are frequently used to survey sites under supervision. Such a system involves the use of a plurality of television cameras which transmit output signals back to one or more monitors which include picture displays, and in nearly all instances there are fewer monitors than cameras. The output signals are transmitted to the monitor(s) by means of coaxial cable, and switching means are provided at the monitors for connecting the cameras to the monitors as required.

These known arrangements are relatively extravagant with coaxial cable, involving a full cable run from each camera to the monitoring point. The number of cable runs corresponds, therefore, to the number of cameras, in spite of the fact that the lesser number of monitors means that the signals from only some of the cameras can be in use at any one time.

An object of the present invention is to provide an arrangement in which more economical use is made of the coaxial cable.

With this object in view, the present invention provides a closed-circuit television surveillance system comprising a plurality of cameras installed at respective locations to be surveyed, one or more monitors, fewer in number than the cameras, disposed at a monitor point, coaxial cables, corresponding in number to the number of monitors, extending between the monitors and the cameras, switch means at each camera to enable it to supply its output signal to the cables, and control means for controlling the switches for providing corresponding displays at the monitors.

Each camera may have a respective function control associated therewith, the control means serving, also, to supply control signals to said function control for effecting selected functions, such as panning, (which is rotational movement of the camera about a vertical axis through the camera) tilting, zooming (which is altering the focal length of the lens and has the effect of decreasing or increasing the area under surveillance), focussing (of the camera lens), window washing, and window wiping (of a housing which protects the camera from rain and snow), at the respective camera.

The control means may conveniently be adapted to control the function controls with high frequency signals by way of the same cables.

The routing of the cables will, of course, vary from site to site. Advantageously, the routing is in the form of a ring; then, if the ring should be broken or severed, signals may still be returned to the monitors.

The invention will be described further. by wav of example, with reference to the accompanying drawings. in which; Fig. 1 is a block diagram illustrating, diagrammatically, the circuitry generally employed hitherto in closed-circuit television surveillance systems; Fig. 2 is a diagram comparable with Fig. 1 but illustrating a closedcircuit television surveillance system according to the invention; and Fig. 3 is a diagram comparable with Fig. 2 but illustrating another closed-circuit television surveillance system according to the invention.

In the known closed-circuit television surveillance systems, as shown in Fig. 1 a plurality of cameras, C1, C2. C3, C4, and so on, are connected by respective coaxial cables L1, L2, L3, L4, and soon, to monitors M1 and M2. These monitors M1, M2 incorporate respective switches S1 and S2 operative to provide for the output signals from the cameras C1 to C4 to be received selectively by the monitors M1 and M2, it being understood that the switches S1 and S2 will be interlocked so that at no time is the signal from one of the cameras supplied simultaneously to both monitors. In this arrangement, a respective lead L1 to L4 for each camera C1 to C4 extends over the full distance from camera to monitor.

Turning now to Fig. 2, the preferred embodiment of the closed-circuit television surveillance system of the invention comprises cameras CC1, CC2, CC3, and so on, connected by way of respective switch arrangements S1A, S1B, S2A, S2B; S3A, S3B; and so on, to coaxial cables LL1 and LL2, which in turn connect with respective monitors MUM 1 and MM2. The number of cables, of course, corresponds to the number of monitors which is fewer than the number of cameras.

Also connected to the cables are respective function control units FC1, FC2, FC3, and so on, of which one is associated with each of the cameras. As has been indicated in relation to the function control unit FCI, these units serve, in respect of the respective camera, to control or perform the functions of panning, tilting, zooming, focussing, window washing and window wiping, as well as controlling the respective switch arrangements S1A, S1B; S2A, S2B; and so on, which serve to connect the respective cameras CCI, CC2, CC3, and soon, to the cables LL1 and LL2 and to disconnect them therefrom.

Furthermore, the system includes for each monitor. respective control CU1 and CU2 connected to the cables LL1, LL2 and to one another. as well as respective filters F1 and F2 the function of which is to prevent high frequency control signals from getting to the monitors MM 1 and MM2.

The manner of operation of this system will readily be understood from the foregoing and the diagram. The control units C1 and C2 send out address signals to the function control units FC1, FC2, FC3. and so on, and provide for the output signals from the cameras selectively to the cables LL 1 and LL2 to be supplied to the monitors so that desired displays from selected cameras are provided at the monitors MM 1 and MM2 Of course an address signal to one of the function control units FC1, FC2, FC3, and so on, ordering the output signal from the respective camera CCl, CC2, CC3, and so on, to be supplied to one of the cables LL1 and LL2, also signals the other function control units not to supply output signals from their respective cameras to the chosen line LL1 or LL2. Such a system allows for each monitor MMl and MM2 to be connected to one camera i.e. one monitor to one camera.

The controls CU 1 and CU2 also provide for the cameras, as desired, to perform the functions already mentioned in relation to the function control unit FC1, by way of the same cables LL1 and LL2. For addressing the function control units FC1, FC2, FC3, and soon, the control units CU1 and CU2 supply highfrequency control signals, for example of the order of 20 MHz, to the units FC1.... FC3 and soon. The filters F1 and F2 prevent such signals from interfering with the camera output signals supplied to the monitors, which are not likely to exceed 8 MHz.

The system illustrated in Fig. 2 is complex in that each camera is capable of the many functions so far described. However, such systems are expensive, due to the complex nature of the cameras employed, and often not all of the functions are required for each installation. In fact one often employs in surveillance systems only fixed line cameras which are cameras set to point in one direction and cannot be moved or focussed by remote control. Generally such cameras only have the wash and/or wipe facilities and indeed these facilities are only required when the camera is situated in a wet or dusty environment. A system comprising fixed line cameras is illustrated in Fig. 3 in which similar reference numerals and letters have been allocated to parts which are similar to those already described with reference to Fig. 2.In this embodiment function control units FC1, FC2, FC3 and so on serve only to control respective switch arrangements S1A, Sl B; S2A, S2B; and soon, of their respective cameras CC1, CC2, CC3 to cables LL1 and LL2 under the control of control units CU 1 and CU2.

With the systems of the invention, of course, it is necessary only to provide cables in a single route from the monitors to the cameras, so that there is a substantial saving in cables and installation costs as compared with the prior known systems.

The invention is not confined to the precise details of the foregoing examples, and variations may be made thereto. For instance, the illustrated examples could be modified by making the cables LL1 and LL2 each into a ring so that, in the event of breakage or deliberate severing thereof between the cameras, signals may still be supplied back to the monitors. Of course, the invention can be applied to systems in which there is only one monitor or more than two monitors, it being understood, of course, that the number of monitors will naturally be fewer than the number of cameras.

Claims (7)

Claims

1. A closed-circuit television surveillance system comprising a plurality of cameras installed at respective locations to be surveyed, one or more monitors, fewer in number than the cameras, disposed at a monitor point, coaxial cables, corresponding in number to the number of monitors, extending between the monitors and the cameras, switch means at each camera to enable it to supply its output signal to the cables, and control means for controlling the switches for providing corresponding displays at the monitors.

2. A system as claimed in claim 1 wherein each camera has a respective function control associated therewith.

3. A system as claimed in claim 2 wherein the control means is effective to supply control signals to the function control.

4. A system as claimed in claim 1, 2 or 3 wherein the control means is effective to supply control signals which are high frequency signals by way of the coaxial cables.

5. A system as claimed in claim 4 wherein each monitor has a respective high frequency filter associated therewith.

6. A system as claimed in any preceding claim wherein routing of the cable is in the form of a ring.

7. A closed-circuit television surveillance system substantially as hereinbefore described with reference to and as illustrated in Figs. 2 or Fig. 3 of the accompanying drawings.