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Category: B&P Security Services CCTV BS EN 5013-7 Design Guidelines

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CCTV BS EN 5013-7 Design Guidelines

Selected Extracts from BS EN 5013-7

7.0 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.

7.1 Surveillance Zone Determination Criteria

A CCTV surveillance installation is designed to monitor events of
fundamental importance. These events might be hold up theft, sabotage/vandalism, hazard, evacuation, etc.
Typical examples of monitoring applications are:

• a) perimeter surveillance
• b) access control
• c) safety
• d) property protection

7.2 Criteria for Determining the Number of Cameras & 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 site constraints and service access, may restrict the camera location and increase the possibility of further cameras being required.

7.4 Camera Selection

The selection criteria should take into account the following:

• a) the camera equipment should satisfy the operational requirement under all specified environmental conditions
• b) safety regulations relating to the site

Points to take into consideration:

• a) white balance of colour cameras
• b) electronic iris in relation to picture degrading for highlights
• c) long exposure times in relation to movement blur
• d) spectral sensitivity in relation to the type of illumination
• e) external synchronisation
• f) back-up power supply

7.5 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:

• a) the lens field of view (indicated in the manufacturer’s nominal figure tables) may be reduced by any overscan in the display device
• b) 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
• c) internal lens reflections and ghosting can significantly impair the image
• d) some zoom lenses are subject to ramping whereby the effective aperture number of the lens increases as the focal length is increased
• e) accuracy of the preset shots if fitted

NOTE: Having selected the camera-lens combination, it is recommended that, for difficult scenes, a camera of the type selected should be evaluated in conditions similar to those to be encountered at the installation.

7.6 Recommended Object Sizes

The size of an object (target) on the monitor screen should have a relation to the operator task, e.g. 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:

• a) for identification the target should represent not less than 120% of screen height
• b) for recognition the target should represent not less than 50% of picture height
• c) for detection of an intruder the target should represent not less than 10% of picture height
• d) for crowd control (monitoring) the target should represent no less than 5% of picture height B&P Security Services - CCTV - BS EN 5013-7- Design Guidelines

7.8 Evaluation of Scene & Illumination

The existing lighting should be evaluated for the level, direction and spectral content. Optimal light sources are those which have a spectrum that best matches the camera imaging device response. If additional lighting is required, the number, type, siting and power of the light sources should be determined.

7.9 Selection of the Video Transmission System

There are many methods of video transmission and the suitability of a particular method for a given application should be carefully evaluated. Video transmission may be as simple as a single coaxial cable or as complex as a microwave link or a mix of different transmission means. Consideration should be given to prevailing and potential environmental conditions in those areas where the equipment and/or cables are to be installed.

7.9.1 Main Video Transmission Systems are:

• a) coaxial cable: The type of cable chosen should have a characteristic impedance of 75 Ohms. For long cable runs amplifying or amplifying plus video equalising equipment may be required to meet the above performance
• b) twisted pair transmission: The system uses standard twisted pair cable, typically 120-150 ohm balanced pairs, which requires specialised transmission and receiving equipment
• c) Micro wave and radio frequency transmission: Correct alignment of transmitting and receiving equipment is essential. Systems normally need regulatory authority approval
• d) infra red and laser transmission: This is a line of sight system applicable only to unobstructed signal paths. The output of some transmitting devices can cause eye damage therefore warning labels must be fitted according to the appropriate safety standards. Alignment and rigidity of transmitting and receiving equipment is important. The transmission may be affected by fog, rain, snow etc. and the range can be reduced by such phenomena and this should be taken into account
• e) fibre optic transmission: Commonly available types, together with the appropriate fibre optic connectors should be used. The transmission system should have sufficient dynamic range to overcome all likely system losses and a minimum of 3 cable repairs
• f) slow scan transmission: A system suitable for both public and private telephone and data networks. Many systems are available with widely varying connection and transmission speeds and resolution. System selection should be carefully evaluated against the operational requirement

7.9.2 Selection Criteria for Video Transmission

Considerations for the selection of a transmission means or a combination
of different means are:

• a) bandwidth of the transmission path
• b) signal to noise ratio
• c) signal distortion
• d) distance to be covered
• e) interference immunity
• f) security of communication
• g) constraints in physical installation

NOTE: Signal to noise ratio and signal distortion are cumulative and can cause picture degradation.

7.10 Control Centre Configuration

The operational requirement and personnel available are the factors determining the number of control locations and equipment configuration of the control centre.

7.10.3 Number of Monitors & their Screen Size

The number of monitors should be sufficient to display the maximum number of simultaneous alarms as stated in the operational requirement.
The monitor screen size should be selected in relation to the viewing distance. The recommended viewing distance is approximately 5 times the displayed picture diagonal.
The extracts above are printed with the permission of the British Standards Institute.

Information associated with: B & P Security - Security Services, Intruder Alarms, Access Control, Door Entry & CCTV

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B & P Security Services Ltd
2 Windlesham Court
Guildford Rd
Bagshot
Surrey
GU19 5NG

Tel: 01276 453110
Fax: 01276 451073

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