Monitors designed for CCTV are equipped with picture tubes suitable for continuous work. The use of TV set with video input for displaying still images will result in burning out the luminescent materials and possible damage of the TV set.

Monitor is a device that allows to change electric signals to optical information suitable for the human eye. Monitors should fulfill safety norms, which means that they must have CE certificate. Safety norms describe, among others, maximum accepted electromagnetic and X-ray radiation levels, protection of the user against electric shock, and protection of the device against surges coming from power line.

Before we choose a monitor, we should pay attention to monitor's parameters: resolution - capability of showing details, picture geometry and stability, maximum brightness and contrast etc. Resolution is usually described by the visually distinguishable number of lines (TVL). It is said that color monitors have high resolution when they are able to show above 400 TVL, monochromatic ones - when they reach 1000 TVL. This resolution has no close association with the number of lines ascribed to D/K or B/G standard.

It is also common to describe resolution in number of pixels, especially in the case of modern LCD monitors.

Monitor should work properly up to 90% humidity, and in temperature range from 0⁰ to +40⁰ C. Some manufacturers specify the temperature range from -10⁰ to 55⁰ C.

Usually monitors are powered from 230V AC line power, however, some monitors with diagonal up to 7" can be powered with 12V or 15V DC power source. Power consumption of B/W monitors reaches 50 W for 20" diagonal; for the same diagonal color CRT monitors need twice as much. Color LCD monitors of similar diagonal usually consume 30 - 60 W.

It should be noted that some inner monitor parts work at voltages reaching even 25kV. Therefore it is not allowed for unqualified people to open the casing.

Adjustments.
Besides the power switch, every monitor usually has the following adjustments: H-hold, V-hold, contrast, brightness, color saturation (color monitors), sharpness.

Color LCD monitors.
These monitors became a standard in new CCTV installations. Their biggest advantage is small depth, they need little space on operator's desk, or can even be mounted on a wall in the monitoring center. The popularity of LCD panels in CCTV applications is the result of large scale manufacturing and low price - they are mainly used as computer monitors. However, the typical PC monitors can only be used with devices equipped with VGA output.
The manufacturers of digital video recorders began to equip their products with such interface, or they offer additional composite video/VGA converters, like the M8543 for CP-CAM DVRs.
The group of LCD monitors dedicated for CCTV applications are professional devices with CVBS inputs, e.g. MTC-19A1-3D+VGA M3119. The monitor has standard BNC inputs for connecting any CCTV video devices using PAL standard, like DVR, CCTV camera, video splitter etc.
Another group of displays that are often used in CCTV systems are universal PC/TV LCD implementations, usually available at very competitive price. Aside from built-in TV tuner, the panels have been equipped with video inputs suitable for connecting CCTV devices. Such models are manufactured e.g. by Samsung and LG.
LCD televisions are also used when one needs bigger screens, over 22".
When using analog CCTV cameras, the LCD monitors should have 4:3 aspect ratio. Most of such cameras provide images in this format and they would be deformed on the displays with 16:9 aspect ratio. The latter are used in IP-CCTV systems. The role of DVR is performed by PC and special software that can adjust the images from the cameras to screen parameters of the monitor used.

Small thickness of LCD monitors allows to use them in places where CRT solutions were practically not possible. LCD monitors in metal vandal-proof casings are mounted in vehicles. Larger panels, up to 21", mounted e.g. in buses (public transport) work as information/ advertising/ entertainment screens. The smaller ones, mounted close to the driver, allow him to monitor the inside of the bus.
The main parameters of LCD monitors include maximum contrast and brightness, pixel response time, horizontal and vertical viewing angles. Additional differences concern number of audio and video inputs/outputs, built-in speakers, the way of mounting.
Choosing LCD monitor it is important to know the terms of warranty concerning possible degradation of the screen (falling-out pixels). This phenomenon is not so irritating as in the case of a PC monitor, but also lowers quality of images.

LCD monitor in London's bus.

Monitors with built-in quad or automatic switcher.
There can be find monitors with built-in automatic switcher or quad. For the reason of easy installation, they are used in simple surveillance systems, commonly made by the final user. They have mostly 2 or 4 channels, and they are useful equivalents of simple quad processors. Built-in quad requires additional connectors, for example: alarm connector, connector for instant automatic change to the camera where motion was detected, and for switching on an alarm system. On the front of the monitor, there are channel selection buttons, quad button (division 4x4), and others.

PC monitors - VIDEO/VGA signal converters.
These converters change standard video signal (CVBS) to VGA standard. They allow to connect CCTV camera, satellite tuner, DVD player, video cassette recorder or other video signal source to standard VGA monitor.

15-AD01 M1688 - VIDEO/VGA signal converter

Audio path in CCTV monitors
Many monitors are equipped with built-in audio amplifiers and speakers. It allows to listen in at the camera's location thanks to microphone built in the camera or placed in the bracket. As the connectors there are used chinches (RCA) or 3.5mm mini-jacks. Audio module requires input signal within range of 10 - 150 mV_p-p Additional volume adjustment can be found on front panel. Presently, 90 percent of sold monitors are equipped with speakers. It is related to the fact that most of offered DVRs also have audio recording feature. And in the case of audio playback the user does not have to worry about purchasing additional loudspeakers.

Criteria governing choice of monitors
Choice of color or B/W monitor depends mainly on the features of monitored objects. It is also important to pay attention to the prospective system in which the monitor may work in the future. If we consider the fact that nowadays the price of video surveillance system working in color is not drastically higher than B/W one, it is worth to choose color system. Practically all currently sold monitors work in color.

Selection of monitors.
As regards diagonal, there are monitors from 4 to 26 inches. Typical diagonal, recommended for operation with a quad or multiplexer with 4 - 9 inputs is 15", for 4 input versions - 12" is enough. Popular small 5.5" monitors are used when there is not enough space or as secondary ones, usually for full screen viewing. When selecting the size of a monitor, one should take into consideration comfort and ergonomics of the final user (guard) who watches the screen. The general rule - the bigger the better (of course not in a small hole). The job is easier with cheap, large and thin LCD monitors.

Size of objects on monitor screen Accordingly to EN 50132-7 norm, the size should depend on operator's duties, e.g. identification, recognition, detection or control. If the observed object is a man, and the effective resolution of installed CCTV system is higher than 400 TVL, the recommended sizes of objects are:

• for identification purposes - object should cover at least 120% of screen height;
• for recognition purposes - object should cover at least 50% of screen height;
• for purposes of intrusion detection - object should cover at least 10% of screen height;
• for the purpose of crowd's control - object should cover at least 5% of screen height.

Number of monitors and their sizes. Number of monitors should be based on:

• number of installed cameras;
• functional features;
• number of operators working at the same time.

Number of cameras to number of monitors ratio shouldn't usually be higher than 10:1.
The number should allow to display all simultaneous alarms (given in user specification requirements).

Size of screen should also be adequate to the distance from which the screen is watched.

Recommended distance between eyes and screen is approximately 3 - 5 times larger than the diagonal (it also depends on resolution of the image).