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CCTV System Design Considerations (Part Two)
Control Room Design:
The control room is the heart of any operations and is the final link in a CCTV system. Unfortunately, control room design is often an afterthought and receives little attention as to location, size and comfort.
The operators spend long hours in this place and their comfort should be taken care of and therefore adequate care should be taken for an ergonomic design. Often the investment in the manpower in the control room may be more than the investment in the CCTV system. All this calls for better planning of the control room design. There are two main aspects that must be considered; Control room layout and Rack design.
High temperature in a room produces fatigue, which can reduce the concentration of the operators. The right temperature should be maintained in the control room at all times.
The room size should be comfortable so that the operators do not feel cramped. Future expansion should be taken into account while determining the room size.
Looking at greenery definitely reduces stress and improves concentration. It is better if the control room has a window and one can see the outside world. This may not be possible in high security control rooms. In such cases adding greenery, plants and other interior design elements in the room will help performance.
Make sure the background noise is maintained to the minimum. Total silence is also not very good, because it may lead to sleepiness. Soothing music is often a good idea.
In any office, the expected lighting is around 400 lux. However in the control room the lighting levels should be much lower. The maximum recommended is around 300 lux. Make sure all the lighting is indirect in nature. Direct lighting behind the operator can cause glare and reflection, causing difficulty for the operator to see the image on the monitor.
It is very important to have an ergonomically designed rack so that the operator can use it effectively and efficiently.
The most comfortable angles for human vision are 45 deg horizontal and 30 deg vertical. Greater angles can be seen but that would involve moving the eyeball or moving the neck. This additional movement can cause fatigue and stress. All efforts should therefore be made to place all the monitors within this vision. The following formula can help in identifying this area.
W = 2 D * tan 22.5 = .82 D
H = 2 D * tan 15 = .54 D
W= Width of view
D= Distance of operator from monitor
H = Height of view
Monitor Arrangement The lesser the number of monitors to view, the better it is for an operator. For ease of observation, it is always best to place the monitor in a array of 3 X3 or 4 X 4. It is more convenient for the operator if the upper rows of monitors are slanted downwards and the lower row is slanted upwards. For a big rack a semi circular design is more convenient.
Ventilation in the Rack:
One of the causes for monitor failure is the heat generated by the monitors when placed in a closed rack. Adequate ventilation should be provided in the rack design.
Wires into the Rack:
After all the equipment is put into a rack, there is a tendency to push the co-axial cable into the rack. This can be a source of problems. Bending the co-axial cable can change the impedance. This can cause picture reflections leading to double images. Too much bending at the equipment end can also damage the BNC connection over time. This will lead to a gradual drop of picture quality.
The distance the operator should sit from the rack will depend upon the resolving power. If you sit very far you will not be able to identify small movements or objects on the screen. In fact, according to one study, the resolving power on a 12 in monitor reduces from 600 lines at 1 foot (30.5 cm) to only 125 lines at 6 feet (1.83m). Choosing the correct viewing distance is important.