CCTV

System Design Criteria

To minimise response times, cameras, monitors, video recorders, etc should be continuously on and the system should not generate more information than the operators can effectively manage.

Surveillance Zone Determination Criteria

A CCTV surveillance installation is designed to monitor events of fundamental importance. These events might be hold ups, theft, sabotage/vandalism, hazard, evacuation etc.

Criteria for Determining the Number of Cameras and Their Location

Once zones and objects requiring surveillance have been identified the number of cameras required can be determined by the fields of view of the cameras, equipment and system resolution and the nature of the zones to be surveyed. Picture detail should be consistent and adequate for the required level of service.

The operational requirement of the system and its use, as well as the site restraints and service access, may restrict the camera location and increase the possibility of further cameras being required.

Camera Selection

The selection criteria should take into account the following:-

• The camera equipment should satisfy the operational requirement under all specified environmental conditions.
  
• Safety regulations relating to the site.

Points to Take into Consideration

• White balance of colour cameras.
  
• Electronic iris in relation to picture degrading for highlights.
  
• Long exposure times in relation to movement blur.
  
• Spectral sensitivity in relation to the type of illumination.
  
• External synchronisation.
  
• Back-up power supply.

Lens Selection

Selection of the correct lens type is as important as the camera selection. A poor lens performance can significantly detract from the overall performance of the system. When selecting the lens the following should be taken into account:-

• The lens field of view (indicated in the manufacturer's nominal figure tables) may be reduced by any overscan in the display device.
  
• The illumination of the sensor in the camera is defined by the aperture number of the lens and its transmission number, which is dependent on the design of the lens.

Recommended Object Sizes

The size of an object (target) on the monitor screen should have a relation to the operator task eg, identification, recognition, detection or monitoring. If the target is a person and the CCTV system has an installed limiting resolution of better than 400 TV lines, the recommended minimum sizes of this target are:-

• For identification the target should represent no less than 120% of the screen height.
  
• For recognition the target should represent not less than 50% of picture height.
  
• For detection of an intruder the target should represent not less than 10% of the picture height.
  
• For crowd control (monitoring) the target should represent no less than 5% of the picture height.

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