Closed-Circuit Television System

a television system in which transmitting cameras are connected to receivers by local communications cables.

Closed-circuit television systems are not used for broadcasting; they have applications in industry, transportation, medicine, and other areas. The mode of image scanning and deflection synchronization, the number of lines, the frame frequency, and other parameters of closed-circuit television systems are determined by the operational purpose of the system and need not comply with standards established for television broadcasting. Transmitting cameras for closed-circuit television systems are usually extremely simple; in most cases they contain only the transmitting tube (a superorthicon if illumination densities are low or a vidicon if illumination densities are high), the deflection system, and the preamplifier for the video signal. Operation of cameras is usually automatic or by remote control. Several types of equipment are produced for closed-circuit television systems. The simplest type is that for single-channel closed-circuit television. Such equipment consists of a transmitting camera and of a receiver; they can be separated by distances of 150–200 m. Current for the deflection systems of the transmitting tube and receiving tube is supplied by a common generator located in the receiver. In this case deflection synchronization and generation of a complete television signal are not required. The more complex, multichannel closed-circuit television systems usually consist of a set of single-channel systems, with a common terminal block added for camera control and switching. Receivers in such systems can be located at a distance of 1–2 km from the transmitting camera.