CCTV: know the essentials

Closed-circuit television (CCTV) is recognised as an expanding and essential system as it continues to take on further roles that demand remote monitoring and becomes more integrated with building management services.

CCTV is part of the digital revolution that includes enhanced communications, IP video networking and an increasing display of video images on PCs and even mobile phones.

However, there are times when we need to go back a stage to remind ourselves of the basics.

Although there are a range of CCTV kits available with a serious role to play, most are limited to working within controlled parameters, because these packages are not designed by the manufacturer to be widely customised or expanded to any great extent.

But if we are aware of the essential role of all of the mainstream components that are used within the CCTV installation industry, it enables all electrical personnel to specify and select a more diverse range of products and facilities in order to form a system to professional industry standards.

We can use a vast array of component parts to install CCTV at a higher level. Accepting this philosophy, I would say that within the security systems installation sector at foundation level the essential devices are: cameras, lenses, cables, and recording and monitoring equipment.

Cameras

Monochrome (black and white) cameras are superior to colour in low light conditions and can be matched to infrared (IR) illumination, which is not visible to the human eye.

Colour cameras are best for identifying and tracking targets.

Colour/mono (day/night) cameras give colour images in normal light, but when light levels become low they switch to black and white.

Dome cameras are used for aesthetic reasons or to conceal the camera’s field of view.

IR colour/mono cameras consist of an assembly containing a camera, lens and integral LED array. They switch from colour to mono in low light conditions and trigger the IR unit, which has a specified effective range.

Pan, tilt and zoom (PTZ) and fully functional cameras have a motorised assembly capable of carrying out a range of camera operations to track and identify moving targets.

Remember that the images from the camera will be referred to as ‘standard’ or ‘high resolution’. The latter involves the ability to resolve fine detail in the picture. Cameras are available with a multitude of housings to cater for different environmental conditions.

Lenses

The lens is an optical device that gathers light from the scene and focuses it at the electronic pick-up imaging device of the camera. We are interested in three main types of lens.

Fixed-focus lenses have a fixed focal length and are used when the field (angle) of view is not going to be adjusted. The focal length determines the field of view at a given distance and needs careful selection to ensure that the correct area is in view and the detail of the scene is acceptable.

Vari-focal lenses allow the focal length to be adjusted during the installation so the field of view or scene can be altered to a certain extent. This allows a limited margin of error.

Zoom or telephoto lenses produce a high magnification but a narrow field of view. Motorised zoom lenses allow an operator to automatically zoom in and out and change the field of view.

Remember that not only is the field of view very important but also the lighting at the scene. No available light at the scene for the lens means no picture at the monitor.

So we need to understand the following.

The light reaching the camera sensor is regulated by the lens iris. The fundamentals of the lens in relation to the operation of the iris are:

• Manual iris lenses are only used where light levels remain constant, typically in internal applications.
• Auto iris lenses adjust to changes in the lighting levels.
• Aspherical lenses have special optics for low lighting installations.
• IR-corrected lenses are used for night-time use with IR lighting and are capable of producing a vivid picture.

Remember to check that the camera and lens are compatible as the iris has to be controlled by the camera’s electronics drive circuits.

Cables

In terms of the media used for carrying the video image, the cables most used in traditional systems are:

• Coaxial. The original wiring medium terminated with BNC connectors. It has a centre copper conductor that is insulated and then screened by an outer shield or braid.
• RG59 has a solid centre conductor and is used in fixed wiring. URM70 has a multi-stranded centre conductor that is superior where cable flexibility is required, such as at PTZ heads.
• Cat 5. Is superior to coaxial cable for long-distance transmission. The twists give the cable pairs added protection against electrical interference.

Remember that Cat 5 cabling should never be replaced by standard twisted pair, multi-core or screened cable as this will affect system performance. Note also that some specialist line-fed cameras, for example those with power and video information in the same cable, use more specific wiring types, as recommended by the manufacturer.

Recording and monitoring equipment

This is used to record the video images, allow access to them for viewing purposes and provide supporting evidence.

The recording equipment allows for a number of cameras to be displayed on one ‘user-defined screen’, with perhaps slave monitors at other locations.

A digital video recorder (DVR) is used to record CCTV images digitally onto a built-in hard drive from one or more cameras. The stored data can then be replayed locally at the DVR through a monitor, on a PC connected to the DVR through a local area network (LAN), or via the internet by means of an asymmetric digital subscriber line (ADSL) connection.

Critical information can be downloaded from the DVR to a networked PC or the files copied to a CD/DVD, or to an external hard drive for larger amounts of data.

Remember that the DVR takes on and replaces the original role of both the multiplexer and VCR used in old analogue systems.

Inputs, outputs and telemetry

All recording equipment has an ability to receive alarm inputs and operate alarm outputs so as to respond to any activity generated manually or automatically. Outputs are used to start up ancillary equipment.

Video motion detection (VMD) techniques analyse the camera picture content to look for changes in the scene so as to start a recording sequence.

Telemetry, which is effectively a signalling system is used to control functions at the camera head such as pan, tilt, zoom and wash/wipe functions. The control data is sent from the controller to receivers, which interpret the signal being sent and then operate an appropriate relay to drive the particular device.

Monitoring equipment

A CCTV monitor is similar to a television receiver, but does not include the tuning circuits. Most monitors have two BNC connectors. One is provided to accept the composite video to display the images on the screen. The other provides a facility to loop through to an additional monitor (slave) or to connect a further item of equipment. At the point the video picture terminates it should be set at 75 ohms. When supplementary equipment to view the same scenes is to be fed from the monitor, it should be set to the Hi Z (high impedance) position.

Illumination and maintenance

Another important thing to remember is that BS 8418:2003, which relates to detector-activated CCTV, recommends that 'there should be sufficient lights on site to illuminate the camera's field of view’, since without sufficient light at the scene being viewed by the camera there can be no picture at the monitor.

In broad terms, when natural light is unavailable, we need to provide illumination for CCTV by installing general overt lighting (visible radiation) or IR covert illumination.

IR is of a wavelength that is not visible to the human eye but which the monochrome camera can ‘see’. If high-quality pictures with good colour discrimination are required at night, this can only be achieved by using true white light, but it must be balanced against light pollution.

Note that the golden white light of Son gives reasonable light levels for CCTV, but the yellow tinge of Sox is poor.

Always provide even illumination over the scene; do not let the camera view the light source direct as this will cause bright patches or light spots, and never create overexposure by using excessive lighting levels.

IR lighting is designed specifically for use with black-and-white CCTV cameras. Traditionally it used a tungsten halogen bulb mounted in a special housing and fitted with a filter to cut off the visible light.

However, new generation, solid-state, high-efficiency, LED, infrared array illuminators are becoming common. With all IR lighting the angle of illumination is matched to the camera lens combination.

As an example, an 8 mm lens provides a horizontal field of view in the order of 30o, so to correctly illuminate the scene, a 30o lamp would be employed. If a narrower spot lamp device was used, the illumination would be too intense.

In conclusion, do not forget that the installation of CCTV will require ongoing maintenance, and the British Security Industry Association’s Code of Practice 109 will apply.