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Closed circuit television (CCTV) - What is CCTV ?

CCTV is a collection of video cameras used for video surveillance.

 

CCTV is different from broadcast television as all the equipment is directly connected together with cables or wireless transmitters that can not be received by standard television aerials or equipment.The transmissions of the video signals are only intended to be accessible by the equipment on its dedicated closed circuit.

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CCTV is generally used in areas where there is an increased need for security, such as banks, airports and town centres. CCTV was initially developed as a means to increase security for banks but over time it has developed into a cost effective means of general video surveillance and home security.

A basic CCTV system comprises of the following;

  • Camera, lens and power supply.
  • Recording device, VCR or a digital video recorder.
  • A monitor.
  • Wiring

CCTV Cameras

CCTV Cameras are available in colour, monochrome or cameras that have the ability to switch between colour and monochrome (day/night cctv cameras). The cctv cameras that switch between colour and monochrome are intended for environments of low lighting at various times. There are 2 reasons for using a cctv camera that can switch between colour and monochrome, monochrome cctv cameras are much more sensitive to low lighting environments, and monochrome cctv cameras can also be used with Infra red lighting. When there is adequate available light there is the added advantage of using a colour cctv camera for recording colour information, for example the colour of a car or a person’s clothing.

The primary function of a cctv camera is to convert light into a video signal, all cctv cameras require an optical lens to focus the light onto an image sensor located directly behind the lens inside the cctv camera.

There are two types of image sensor available, a cctv camera with a CMOS (Complementary Metal- Oxide Semiconductor) image sensor chip and the other more common type that uses a CCD (Charge Coupled Device) imaging sensor chip. The majority of CCTV cameras and Video Camcorders use a CCD imaging sensor, whereas CMOS imaging sensors are more commonly used in webcams, budget home security cameras and digital photography cameras. CCD cameras are capable of creating a much clearer and higher resolution image.

Different types of cctv cameras are Board Cameras,C Mount Cameras,IR Cameras,IP Cameras,Zoom Cameras,Speed Dome Cameras.

All cctv cameras require a power supply, these are usually 12 volts DC, 24 volts AC or 240 volts AC.

CCTV Lenses

As mentioned in the section on cctv cameras, all cctv cameras require an optical lens. The job of the lens is to limit and focus light onto the image sensor of the cctv camera. A lens can also automatically control the amount of light that reaches the imaging sensor, these lenses are referred to as Auto Iris (AI) lenses and are generally used outdoors where the light changes constantly during the day, at night and also in varying weather conditions.

It is also the job of the lens to control the depth of field of the image, either for a wide angle image or a narrow angle image depending on the distance of the object in question from the cctv camera. Where movable cctv cameras are used a zoom lens is usually fitted to allow varying points of a monitored area to be viewed. Zoom lenses are usually controlled by the CCTV operator.

CCTV Recording Devices

The recording device receives and stores the images from the cctv camera, previously time lapsed VCR’s and video multiplexers were generally used in CCTV systems, but due to developments in technology digital video recorders are now more commonly used.

Time lapse VCR’s allow cctv camera images to be recorded for varying lengths of time on a single 3 hour video tape, from lengths of 3 hours to over 960 hours. The problem with time lapse video recorders is that the longer they are set to record for the less video information they can record per second, similar to taking a photograph from 25 every second to one photograph every 4 seconds for example.

Digital video recorders use computer hard drives to store the recorded information and can however record for much longer depending on the size of the hard drive and the CODEC being used. A DVR combines and enhances the recording capabilities of a time lapse VCR and a multiplexer.

CCTV VCR and CCTV Camera Switcher

When there is a requirement for recording more than one cctv camera and video switcher can be used, the cameras are connected into the switcher and the switcher will automatically switch the image being fed to the monitor and the video. The disadvantage of using a switcher is that if there is an incident it is possible that the cctv camera image will change causing the incident to be missed.

CCTV VCR and CCTV Video multiplexer

A multiplexer is a device that takes multiple video images and lays them onto a VHS tape, it uses the properties of the PAL signal to record as many images from multiple cctv cameras every second as possible. The video information recorded is limited by the amount of cctv cameras on the system and the length of time the VCR is set to record for.

CCTV Stand alone digital video recorder

A stand alone DVR is designed specifically for CCTV systems. It uses computer hard drives to store video information and an embedded operating system to control the functions of the DVR, this type of recording device is most commonly used with current CCTV systems. CCTV Digital video recorders have various settings to enable more video information to be recorded at the required times using technology such as video motion detection, this means that the images from the cctv cameras are only recorded when the information of the image changes, for example a person walking in front of the cctv camera.

As previously mentioned, CCTV DVRs have a multiplexer built in which enables the user to view multiple images on the screen at any given time by segregating the screen image.

Many DVRs can also be connected to a network or a modem to allow remote access.

CCTV DVR Comes with High Contrast LCD Display is called Media DVR.

CCTV PC based digital recorder

PC based cctv DVR operate much in the way as stand alone cctv DVRs, but use video capture cards and additional software to carry out the operations of the DVR, these types of DVR can easily be upgraded to accept additional cameras by adding more capture cards. As with the stand alone DVR’s, PC based recorders can also be connected to the internet for remote access to the DVR.

CCTV Network video server

Network video servers are designed for IP CCTV cameras over WAN or LAN computer networks where each camera has its own unique IP address.

CCTV Monitor

There are two main types of monitor; the analogue monitor referred to as a CRT ( Cathode Ray Tube) and the digital monitor which is the commonly used PC monitor known as the TFT ( Thin Film Transistor) monitor.

There are advantages and disadvantages for both monitors, A TFT monitor is less space consuming than a CRT monitor. A CRT monitor will display a better image of low and medium resolution cameras than a TFT monitor. For high resolution cameras, a TFT monitor can be more cost effective than using a high resolution CRT monitor.

CRT monitors are usually specifically designed for CCTV systems and come fitted with a composite video input BNC (Bayonet Nut Coupling) plug. CCTV monitors are also designed for long term use compared to standard TVs and cater for higher screen resolutions.

Developed in the late 1940’s as a miniature version of the Type C connector, Bayonet Neil-Concelman (sometimes erroneously called a British Naval Connector or Bayonet Nut Connector). A connector widely used in the CCTV industry, usually for coaxial cable. Easy to install and reliable with little video signal loss. A rotating ring outside the tube locks the cable to any female connector.

CCTV Lighting

All cctv cameras require a degree of lighting to be able to pick up an image, monochrome cameras generally work well in darker environments than colour cctv cameras. Infrared lighting can also be used with monochrome cctv cameras.

There are various types or infrared lighting available, standard bulbs or LED ( Light Emitting Diode) types.

Infra red lighting can illuminate areas at different frequencies, although invisible to the naked eye, CCTV cameras can see the light emitted. Depending on the frequency range that the IR lamp operates, depends on how visible the lamp glow is to the naked eye. Note however, not all cameras are sensitive enough to pick up all frequencies of infra red.

Covert CCTV Camera

Covert CCTV is the practice of using video cameras in locations that are not made obvious to the persons being monitored in the specific cctv camera coverage area, but it is recommended that there is reasonable cause for the purpose of covert surveillance and that its primary objectives are clearly noted, only used for the purposes of preventing crime and are not used for longer than intended.

Remote CCTV

Remote CCTV is the means of accessing CCTV images over a computer network or standard telephone networks. Software is used on the local PC that allows access to the digital video recorder.

CCTV IP CAMERA

IP CCTV refers to Internet Protocol Closed Circuit Television; traditional CCTV systems use digital or analogue cameras using analogue cables that connect to a recording device such as a digital video recorder. IP cctv cameras are designed to plug onto any existing wired or wireless computer TCP/IP network, or directly onto a broadband connection so that the cctv camera can be accessed by any computer connected to the network, this includes over the internet.

Computers are used on the network to store the cctv camera images but with the flexibility of IP CCTV, the cctv cameras could be located on opposite sides of the world. Although IP Cctv Cameras can be connected directly to an existing network, bandwidth is always a consideration as the data sent from the cctv camera is likely to be much larger than standard data transferred over usual office networks which if not planned correctly can slow down the entire network.

CCTV Video Signal

The video signal is known as the moving image information signal produced from a video camera, we use a video signal standard called PAL (Phase Alternate Line) this is a colour or monochrome video signal that comprises of 25 images or frames per second. A new breed of CCTV cameras referred to as IP CCTV Cameras (Internet Protocol Closed Circuit TeleVision) uses a data signal which comprises of a series of computer readable still images. These cctv cameras are generally connected directly to a computer or a computer network and are accessed by software to enable the live viewing, recording and playback of the video images. One format for this moving video data is called MPEG (Moving Pictures Experts Group).

CCTV Video Transmission

Video transmission is the means of getting the video signal from the camera to the recording or monitoring device. The transmission can be carried over wires or over the airwaves via radio transmission.

The most commonly used cable for wired transmission is RG6 coaxial cable.

Network cable is being used more commonly as video is able to travel further along twisted pair cables than standard coax.

Other forms of video transmission include fibre optic cables, microwave transmission and licence free radio transmission.

CCTV Resolution

Resolution refers to the number of definable parts of the horizontal image produced by a camera, recorded by the video or digital video recorder and displayed on the monitor.

CCTV equipment manufacturers refer to this as TVL (TeleVision Lines). Minimum of 420 TVL is recommandable.

The TVL of the analogue PAL video information is closely compared to the pixels of a digital image.

VHS (Video Home System) recorders are capable of recording 300 lines of a monochrome image or 240 lines of a colour image, SVHS (Super Video Home System) is capable of recording 400 lines of monochrome image and 340 lines of a colour image.

The recording device should be the deciding factor when choosing the resolution of a camera as a 520 TVL camera being recorded on a VHS recorder will only record 240 lines out of the available 520 lines.

Digital Video Recorders (DVRs) have the advantage of being able to convert the analogue PAL signal into a digital signal at various resolutions, the downside is, that the higher the resolution of the image recorded, the larger the file size of that digital image. The conversion of the analogue PAL signal to a digital image is done using a CODEC (COmpressor-DECompressor).

CCTV Codec's

A CODEC is used to convert an analogue video signal to a digital video signal either using hardware or software. Codec's play an important role in digital video recorders; they are not only used to convert the analogue signal to a digital signal but to also produce the best quality video information at the smallest file size. This makes a big difference to the amount of video that can be recorded on a DVRs hard drive.

There are many standards of CODEC, those used for video compression that you may come across are MPEG-2, MPEG-4, JPEG 2000, AVI and H.264, H.264 is the latest codec being introduced into the CCTV market, deriving from video conferencing equipment.


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