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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.
Specification of the CCTV camera for a project is not always the easiest of processes. There are many factors that have to be taken into account: technical specifications, the application and its requirements, as well as any physical constraints the site may impose. With ever increasing product ranges available in the marketplace, and technology constantly evolving to optimize performance, reliability and functionality, it is quite a challenge to make an informed decision to meet the requirements for the job whilst remaining within projected budget. Understanding the many variables within CCTV camera technology today can only be an advantage in helping you make the right choices.
At the heart of the CCTV camera technology is a CCD sensor (Charge Coupled Device) that converts light into an electrical signal. This electrical signal is then processed by the camera electronics and converted to a video signal output that can then be either recorded or displayed on to a monitor.
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.
There are several factors that make up a complete camera specification and are all be inter-related. These are:
- Signal to noise ratio
- Automatic gain control
The most common factor people look for in a camera specification is the sensitivity, although it is not always the most important. Sensitivity is the amount of light, in lux, necessary to produce a video signal of some, usually unspecified, level. This factor seems to be the marketing battleground upon which all manufacturers fight to show their cameras as being better than the competition!
Signal to noise ratio. (S/N):
As seems obvious this is the ratio of the level of the video signal to the amount of noise present. Noise in a video is seen as snow or graininess, resulting in a poorly defined image on the monitor or video recording. The unit for expressing s/n ratio is decibels (dB), but do not be too worried because it can be expressed as a ratio. The following table shows the equivalent ratio for values given in dB.
Automatic gain control (AGC):
When the light falling on to an imaging device reduces to a certain level, there is insufficient to create a full level video signal. AGC acts to increase the amount of amplification in these conditions to bring the signal up to the required level. As well as amplifying the video signal, additional noise can be introduced, and the signal to noise ratio reduced. The result is frequently a very much degraded signal and poor picture on the monitor.
The value referred to here is the horizontal resolution in TV lines, that is the number of black to white transitions that can be resolved across the image. This is a function of the number of pixels that make up the CCD imaging area and the bandwidth of the camera circuitry. Typical camera resolution is 350 TV lines, with high resolution cameras producing better than 450 lines. Note that resolution costs money!
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.
CCD means a Charged Coupled Device and consists of a flat array of tiny, light sensitive photodiodes. Each diode produces a voltage that is directly proportional to the amount of light falling on it. No light would produce no voltage and therefore a black level. Maximum light would produce a maximum voltage and therefore a white level. In between these would be shades of gray, and is the luminance information of a video signal. In the case of a color camera, a chrominance signal is superimposed onto the luminance signal to carry the color information. (If a color camera is connected to a monochrome monitor, then a monochrome picture would be produced from the luminance information and the chrominance would not be processed). See also color cameras with separate Y/C outputs under resolution.
So far all the cameras shown have been fixed with fixed focal length lenses. In many applications the area to be covered would need many fixed cameras. The solution to this is to use cameras fixed to a movable platform. This platform can then be controlled from a remote location. The platform may simply rotate in a horizontal plane and is generally known as a scanner. Alternatively the platform may be controllable in both horizontal and vertical planes and is generally known as a pan, tilt unit. A basic system is illustrated in diagram 8.
This chapter does not deal with how cameras are controlled or wired; it is just showing the facilities that may be incorporated into a CCTV system. Therefore the diagrams that follow are simply descriptive block diagrams and not connection drawings.
Cameras may be used indoors or outdoors. When used outdoors they will always require a protective housing. For indoor use the environment or aesthetic constraints will dictate whether a housing is needed. Systems may contain a combination of both fixed and movable cameras.
Covert Cameras, in essence, are a means of offering surveillance of an undetected or more discreet nature. Suitable for use in a broad range of internal applications, these miniature Cameras have been designed in developed to provide monitoring tools that are disguised in the form of everyday commercial and domestic objects.
This ensures that they are able to blend inconspicuously into any background and consequently do not catch people’s attention. As a result, there are a number of state-of-the-art products which have been introduced into the market to meet security demands, varying from office clocks to Passive InfraRed (PIR) sensors, containing a minute camera within. These products are available in monochrome or color versions and with optional audio.
Covert cameras tend to be used where there is a requirement to achieve particular objectives. These tend to fall into the following categories:
A) Covert surveillance - where there is a requirement to monitor activities in a particular location, completely undetected, e.g. in areas of high security like jewelers and banks. They are also useful for back-up surveillance in installations where the primary CCTV equipment is of a more traditional nature, i.e. standard cameras. In this case Covert
Cameras can operate as a back-up where primary cameras are disabled by an intruder.
B) Discreet/Unobtrusive surveillance - often there is a need for a surveillance system that is less conspicuous, not necessarily as an attempt to hide the fact that monitoring is taking place, but more from marketing or style considerations.
When introducing a covert system, it is important to recognize that access to recorded material must be kept to a minimum to ensure the privacy of individuals who may appear. A responsible policy should be introduced to ensure that footage from covert cameras is used for the purposes it was intended.