Closed circuit television

Closed Circuit Television (CCTV)

Closed Circuit Television (CCTV), as the name implies, is a television transmission system in which the electronic elements are closely connected, unlike a broadcast television, where the receiver picks up signals on being correctly tuned to a proper frequency. In this system, signals (either live or prerecorded) are sent to a defined number of receivers. The medium of transmission could be either via coaxial cables or scrambled radio waves that are unscrambled at the point of reception.

A CCTV is as shown below:

(Figure a)

These specialized systems are not restricted to the regulations put forth by the Federal Communications Commission (FCC), but CCTV systems using scrambled radio waves are subject to common carrier tariffs and FCC conditions of service.

Parts of a CCTV:

The CCTV consists of the following parts:

Camera:

The camera is the starting point in a CCTV system. Its main function is to capture the image of the object and transfer it to the viewing monitor. CCTV cameras do not have an inbuilt lens. The lens is a separate object and is screwed onto the front of the camera. A BNC cable is used for connecting the coaxial video cable. Power is provided via this cable. A simple circuit diagram is as shown below:

(Figure 1)

Monitor:

The picture captured by the camera needs to be reproduced. This is done using a viewing monitor. This monitor is similar to the television monitor except that it does not have the tuning circuits.

(Figure 2)

In-Line CCTV: These systems consist of a monitor or video display that is mounted on top of the camera. This system is considered in applications where space is an issue, or where one does not require a 21? monitor for the purpose of viewing. Usually these types of systems are portable or wall mounted.

Out-of-Line CCTV: Usually these systems use a television for the purpose of viewing. The camera sits beside the viewing monitor as it will not be able to bear the load of a 21? television monitor. Some CCTV?s use a computer monitor for the purpose of viewing. These monitors cannot be interchanged with a television as these systems consist of a camera designed specifically to be integrated with the computer monitor. These systems offer access to print material or computer applications or both using a split screen function.

Types of CCTV?s:

Simple CCTV System: The simplest configuration of a CCTV system consists of a camera connected via a coaxial cable to a viewing monitor. The power for the camera is provided by the monitor (the camera, in this case, is called a line powered camera). The picture below shows a simple line powered CCTV system. This is a ?Build It Yourself? type of system.

(Figure 3)

A development to the basic CCTV structure was to incorporate a number of cameras, and view the output from the selected camera on the monitor. The monitor is provided with selection buttons to select the camera whose output is required. Also, a microphone was incorporated to carry sound signals, which was connected to a speaker connected to the monitor. Although this system was cheap and easy to install, reviewing could be tedious when the cameras had to be set to sequence.

Mains Powered CCTV System: In this type of system, the camera is connected to the mains, and so is the monitor. A coaxial cable is used to carry the video signals from the camera to the monitor. This system is also easy to install, and provides greater deal of flexibility when designing complex systems. But a point to note is that this installation must comply with the relevant regulations such as the Institute of Electrical Engineers (now incorporated into British Standard BS7671). Failure to do so could be dangerous and create problems with the validity of insurance. The picture below shows a mains powered CCTV system.

(Figure 4)

Systems with Video Recording: In this type of system, the output pictures depend upon the way in which the switcher is set up. However, there is no control over the images displayed. The picture below shows a system with a video recorder and video switcher.

(Figure 5)

Systems with Movable Cameras: All the above examples seen here used a fixed camera. However, in order to capture images of a large area, many fixed cameras would be needed. A solution to this problem would be to use one camera fixed to a movable platform. This platform could then be controlled from a remote location. The platform could move in a horizontal plane (called scanner), or both horizontal and vertical planes (called pan, tilt unit).

Outdoor cameras would require a protective covering while indoor cameras may or may not require one.

More recent developments have made possible some very sophisticated systems. These include multiple recording of many cameras; almost real time pictures over telephone lines; true real time color pictures over the ISDN telephone lines; switching of hundreds, even thousands, of cameras from many separate control positions to dozens of monitors; reliable detection of movement by electronic evaluation of the video signal; immediate full color prints in seconds from a camera or recording; replacement of manual controls by using touch screen features.

Applications of CCTV:

The main application of CCTV systems is for security purposes in banks, retails stores, etc. The scope for use is however unlimited. Some of the applications where CCTV?s are used are as listed below:

Monitoring traffic on roads

Recording the processes occurring inside dangerous locations in a chemical factory

Surveying traffic in a town/city centre.

Recording time lapses for the animation purposes.

Recording occurrences taking place in a game

Assisting the visually impaired people