How Does a Closed Circuit TV Work?

Features
Closed circuit TV systems can be found in a variety of settings, ranging from banks to stores, airports and military installations. Many homes also employ a closed circuit system. As such, home monitoring systems will be the focus of this article. Surveillance has become a needed presence within today's society, and closed circuit TV systems serve this need well.

The most basic of systems will include a video camera and a monitor. The camera acts as the input device, recording any activities taking place within the space in need of surveillance. The monitor receives this input, and displays the recorded activities. Standard surveillance cameras do not come with a lens because of the varied possible angles available within any one scene. However, the camera screw mount for the lens is a standard thread, so most lens types will fit.

The monitor itself is quite similar to a tv set minus the tuning circuits. If multiple cameras are hooked up to the monitor, a switcher control will allow you to rotate through the areas under surveillance, or maintain input from a single camera. Coaxial cables, telephone wires, fiber optic strands and microwave radio systems are all used as connector cables, running from camera to monitor. The type of system you have in place will determine which connector is needed.

Equipment Options

When selecting a camera for a closed circuit system, lighting considerations will determine which camera is best suited. Camera classifications fall into three categories: general purpose, low lux and color cameras.

Brightly-lit areas will accommodate all three camera types. However, the general purpose and color cameras require bright lighting in order to render a clear picture. Low lux cameras are known for their ability to render dark settings in visible and lighter hues. The drawback with lux cameras is they only provide a black and white output.

Monitor selections deal primarily with size differences. What size monitor to use depends on the viewing distance being recorded. A 9-inch monitor will suffice for viewing distances of 14 to 16 inches. Distances of 36 to 50 inches require a 12-inch monitor. Distances of 50 to 76 inches require a 15 to 19-inch monitor.

Switcher controls are only needed if multiple cameras are hooked up to a single monitor. Switcher controls come in four categories. Manual Passive Switchers are the least expensive option, with a single mechanical switch for rotating through camera views. Homing Sequential Switchers include timer options which allow interval rotations of each camera. Bridging Sequential Switchers work the same as the home sequential option with an addition monitor connection. The second monitor can be set to survey one area in particular as the first camera rotates through scenes from the other cameras. Alarm Programming Sequential Switchers perform the same function as the bridging sequential switcher while providing terminal connectors to each camera.
Rotation functions can be set in intervals, or
programmed in response to a motion sensor signal


Lens Requirements

A clear rendition of the area under surveillance is a primary objective in setting up a closed circuit TV system. As lenses must be purchased separately, there are a couple things to keep in mind when making a selection. Camera lens options vary in focal length, zoom capabilities, iris control and spot filtering.

Focal length and zoom capability will determine how much area the camera will be able to cover. A long focal length provides detailed views at a distance, whereas a short focal length gives a wide view of the immediate scene. The addition of a manual or motorized zoom lens feature provides a closer examination of selected scene details.

Iris control has to do with the amount light that enters through the center of the lens. This feature is necessary if you're using a low light level camera. Manual and automatic control options are available. The spot filter feature is also needed when using the low level camera. Spot filters work in conjunction with the iris control when the lighting in a setting is dim. It works to filter the available light across the field of vision.