The next development was to incorporate the outputs from four cameras into thc monitor. These could be set to
sequence automatically through the cameras or any camera could be held selectively. Diagram 1.4 shows a typical arrangement of such a system. There was even a microphone built into the camera to carry sound, and a speaker in the monitor
Diagram 1. 4 A Four Camera Line Powered CCTV System
The speaker, of course, only puts out the sound of the selected camera. There were however a few disadvantages with the system, although this is not to disparage it. The microphone, being in the camera, tended to pick up sound close to it and not in the area at which it was aimed. There was a noticeable, and sometimes annoying; pause between pictures when switching. This was because the camera was powered down when not selected and it took time for the tube to heat up again.
The system was, though, cheap to buy and simple to install. It came complete in a box with camera, l6mm lens, bracket, switching monitor and 12 metres of coaxial cable with fitted plugs. An outlet socket for a video recorder was provided, although reviewing could be a little tedious when the cameras had been set to sequence. There are now many systems of line powered cameras on the market that are more sophisticated than this basic system. Most of the drawbacks mentioned have been overcome. Cameras had been around for a long time, of course, before this development. The example is given to show the simplest, practical application. The use of some line powered cameras can impose limitations on system design. They do though, offer the advantage of ease of installation.
MAINS POWERED CCTV SYSTEMS
The basic CCTV installation is shown in diagram 1.5 where the camera is mains powered, as is the monitor. A coaxial cable carnes the video signal from the camera to the monitor. Although simple to install it should be borne in mind that the installation must comply with the relevant regulations such as British Standard BS 7671. Failure to do so could be dangerous and create problems with the validity of insurance.
Diagram 1. 5 A Basic Mains Powered CCTV System
This arrangement allows for a great deal more flexibility in designing complex systems. When more than one camera is required, then a video switcher must be included as shown in diagram 1.6. Using this switcher, any camera may be selected to be held on the screen or it can be set to sequence in turn through all the cameras. Usually the time that each camera is shown may be adjusted by a control knob or by a screwdriver.
SYSTEMS WITH VIDEO RECORDING
The next development of a basic system is to add a video recorder. The arrangement would be as shown in diagram 1.7.
Diagram 1. 7 A Multi Camera System With Video Recorder
With this arrangement, the pictures shown during playback will be according to the way in which the switcher was set up when recording. That is, if it was set to sequence then the sequenced views will be displayed on the monitor. There is no control over what can be displayed.
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