Introduction

As the name implies, it 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 article introduces the main components that can go to make up CCTV systems of varying complexity.

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 find 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 stadiums.

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 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 fitted 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 Camera And Lens

Not all lenses have focus and iris adjustment. Most have iris adjustment. Some very wide angle lenses do not have a focus ring. The 'BNC' plug is for connecting the coaxial video cable. Line powered cameras do not have the mains cable. Power is provided via the coaxial cable.