(reproduced from "The Principles and Practice of CCTV" by Mike Constant and Philip Ridgeon) 
INTRODUCTION
As the name implies, CCTV is a system in which the circuit is closed and all the elements are directly connected. This is unlike broadcast television where any receiver that is correctly tuned can pick up the signal from the airwaves. Directly connected in this context includes systems linked by microwave, infrared beams, etc. This Chapter introduces the main components that can go to make up CCTV systems of varying complexity. Each part is described in greater detail in other chapters.
THE APPLICATIONS FOR CCTV
Probably the most widely known use of CCTV is in security systems and such applications as retail shops, banks, government establishments, etc. The true scope for applications is almost unlimited. Some examples are listed below.
Monitoring traffic on a bridge.
Recording the inside of a baking oven to imd the cause of problems.
A temporary system to carry out a traffic survey in a town centre.
Time lapse recording for the animation of plasticine puppets.
Used by the stage manager of a show to see obscured parts of a set. The well publicised use at football stadia.
Hidden in buses to control vandalism.
Recording the birth of a gorilla at a zoo.
Making a wildlife program using a large model helicopter.
Reproducing the infrared vision of a goldfish!
Aerial photography from a hot air balloon.
Production control in a factory.
The list is almost endless and only limited by the imagination.
THE CAMERA
The starting point for any CCTV ( Closed Circuit television )system must be the camera.
The camera creates the picture that will be transmitted to the control position.
Apart from special designs, CCTV cameras are not iitted with a lens.
The lens must be provided separately and screwed onto the front of the camera.
There is a standard screw thread for CCTV cameras, although there are different types of lens mounts.
Diagram 1.1 Camera and Lens
THE MONITOR
The picture created by the camera needs to be reproduced at the control position. A CCTV monitor is virtually the same as a television receiver except that it does not have the tuning circuits.
Diagram 1. 2 CCTV Monitor
SIMPLE CCTV SYSTEMS
The simplest system is a camera connected directly to a monitor by a coaxial cable, with the power for the camera being provided from the monitor. 'This is known as a line powered camera. Diagram 1.3 shows such a system. Probably the earliest well known version of this was the Pye Observation System that popularised the concept of CCTV mainly in retail establishments. It was an affordable, do-it-yourself, self contained system.
Diagram 1. 3 A Basic Line Powered CCTV System
| Next page >>
