Since the introduction of closed circuit television (CCTV) systems in the ‘70s, sales have generally increased each year, but never to the extent that they’re expected to grow over the next three years. According to Ross & Baruzzini, an airport security engineering firm, the video surveillance market that was once worth slightly more than $1.11 million in 2000, is expected to balloon to nearly $4 billion by 2006.
Law enforcement, hospitals, colleges, manufacturing plants, and shopping malls all use CCTV systems to identify the movement of employees, visitors, and intruders. Additionally, numerous industries use CCTV to more closely monitor high-risk rooms or areas that contain hazardous materials in which employees are at a greater risk of injury.
Any CCTV security project should be installed according to recommended procedures and standards and tested to assure consistent quality performance, which is achievable if you have the proper tools and test equipment and know how to use them. And just now as demand has skyrocketed, the cost has dropped substantially. About 15 years ago, an oscilloscope cost about $3,000, but today you can buy a quality portable oscilloscope for less than $1,000, and several hand-held video meters are also currently available.
The three basic components of a CCTV security system are the camera, the monitor, and the communications medium, or cable.
The camera. The heart of a video security system is the camera, which unlike the human eye, can’t adjust to various focal lengths and light conditions automatically. Instead, it’s limited to a fixed field of view, a pre-determined focal length, and defined light sensitivity.
Better quality cameras typically use charged coupled device (CCD) chips, which are available in 0.5-in., 0.33-in., or 0.25-in. sizes, to produce images. In most cases, the larger the chip, the higher the image quality and the higher the price.
CCD cameras can be divided into three classifications based on lighting conditions.
- General-purpose cameras.
Best suited for indoor surveillance, these cameras require relatively high light levels and even illumination to achieve a satisfactory image without the aid of auto-iris lenses or infrared illumination.
- Low-lux cameras.
Because they only operate in the black and white spectrum, typical low-lux cameras can operate at a lux as low as 0.5, which is near blackness to the human eye. As lux approaches 0, images become harder for the human eye to register.
- Color cameras.
They may be able to provide better recognition characteristics, but these cameras need a much higher level of light than a black and white camera to do it.
For each camera you install in the system, you must also decide what type of lens will provide the best field of view, based on its operating light range and power supply. The lens will determine the area viewed by the camera and help the camera adjust to varying light conditions.
The amount of area “seen” and transmitted by a camera is determined by the focal length of the lens and whether the camera is equipped with a zoom function. The focal length of the lens determines the camera’s field-of-view. Short focal length lenses (3.6 mm to 16 mm) have a wide field of view and display more of the scene. Long focal length lenses (40 mm to 135 mm) have a telephoto effect and provide more detailed views of distant objects.
Fixed focal length lenses have a permanent field of view and offer the most economical solution for general surveillance situations. Manual zoom lenses allow the user to adjust the view by hand at the camera location. Motorized zoom lenses allow the viewer at the monitoring station to control the field of view.
The iris is a variable shutter or opening in the lens that can be closed to limit the amount of light that enters the camera. Most low-level cameras require lenses with automatic iris control. Auto-iris lenses are electrically controlled by the camera, but can be overridden with remote controls at the monitor location.
The performance of 115VAC and 24VAC camera units is identical. The deciding factor is the cost of the power supply conductors. A 115V unit can use low gage conductors for a very long run, but the NEC or a local ordinance may require conduit encasement. A 24V unit may require heavier gage conductors, but conduit isn’t normally required.
Motorized pan, tilt, and zoom (PTZ) cameras have become more affordable and offer better performance than cameras manufactured just a few years ago. PTZ cameras can rotate horizontally 360°, vertically 90°, and have electrically powered zoom lenses.
Camera accessories a cable guard to reduce cable wear and prevent tangling, housings for both indoor and outdoor installations, and additional accessories for the outdoor housings, such as heater, blower, or window wiper. A variety of wall, ceiling, and pedestal mounts completes the list.
The monitoring station. Selection and placement of monitors is fairly simple, but very important. Consider the viewing distance first before recommending a monitor size. Supplementary components used at the monitoring station include the video splitter and various types of switchers that are used to switch the view from one camera to the next, and the inserter/splitter/picture-in picture, which splits the screen on a single monitor to simultaneously accommodate pictures from two cameras. Other components necessary to complete the installation include the video cassette recorders and the video motion detectors.
Security teams at large installations with many cameras to monitor would benefit greatly from installing monitors that provide sequential switching of camera views. Without them, security personnel could become overwhelmed by trying to watch too many monitors. Sequencers, which automatically switch monitors from one camera to another in a preset sequence are also a valuable addition to any system.
VCRs provide security records that are important when you're trying to analyze an intrusion or other event, and two types are best suited for security surveillance systems.
Time-lapse video recorders use microprocessor-based time-lapse techniques to compress long periods of recording time into a short length of tape. The quality isn’t as good as a standard videotape, but you can squeeze up to 600 hr of recording onto a standard T-120 cassette. Most units come with automatic speed switching mechanisms, which increase the recording speed to standard when an alarm triggers.
Event alarm recorders. These devices have many of the same features as time-lapse recorders, but they don’t turn on unless triggered by an alarm. After the alarm, they record for a programmed period of time and then shut off until the next alarm condition. Both types of recorders should have built-in character generators that identify which camera is displaying the area where the alarm condition exists.
Video motion detectors can also be used to detect irregular motion in the camera's field of view, which will set off an alarm. Not only will this alert security guards to the intrusion, but it may also switch the scene onto a monitor for continuous observation. It may also automatically switch on a VCR and capture the action on film.
The cabling system. The cable used to carry the video signal has changed quite a bit in a relatively short period of time. Coaxial cable, which uses a central conductor surrounded by an insulator and an outer conductor sheath, is the most popular method of carrying video signals. However, fiber optic cable, unshielded twisted-pair copper cable, low bandwidth microwave, Internet and telephone line transmissions are also options for carrying video transmissions when distances from the cameras to the central monitoring station exceed the maximum limit for coaxial cable.
These other media are also gaining in popularity, due in large part to the CCTV industry’s move from the use of analog signaling to the more efficient digital signal transmission technology. A digital network-based surveillance offers scalability, improved storage, and integration potential. For example, digital video standard MPEG 4 has been approved as a professional international standard that supports video surveillance. Compared to MPEG 2, which is used in DVDs, MPEG 4 offers increased flexibility in video scaling and improved resolution.
Thus, CCTV manufacturers and integrators are making the transition to digital and Internet-based video recording. Central server-based authentication for access to cameras on the network will permit control of overall and per-camera network bandwidth usage. The goal is to have secure viewing of the same video feed from multiple locations, or Multicast IP, without using additional network bandwidth.
However coaxial cable is still the dominant medium to consider, and the selection, installation, and termination are all crucial to optimum video performance, because the CCTV video signal is composed of both low-frequency components, such as horizontal and vertical sync pulse information, and high-frequency components, such as video information.
All coaxial cables have a characteristic impedance; the impedance of CCTV equipment is 75 ohms. This means that the camera must have an internal source impedance of 75 ohms and the monitor must have a 75-ohm termination. If you choose a cable of another impedance, signal loss and reflections will degrade picture quality.
Coaxial cables are also available in different RG types. RG, which stands for “radio guide,” refers to the transmission of radio frequency signals along a coaxial cable. The 75-ohm coaxial cable is available in several sizes, the most common types being RG 59, RG 6, RG 7, and RG 11. The RG 59 type is preferred because it’s the smallest in diameter of the three and the easiest to work with. The drawback is that it has the highest attenuation of the three types, and the practical transmission distance is from 750 ft to 1,000 ft.
The cable’s center conductor should be made of bare copper, not a copper-covered steel center, which is suitable for CATV use, and the shielding should be constructed of bare copper to provide a low D.C.R. return path. It should have a 95% or better braid coverage to provide adequate shielding from outside electrical interference. Additionally, while a solid conductor is acceptable for a fixed camera, if the cable attaches to a PTZ unit, a standard conductor should be specified.
The environment determines the jacket material choice. While PVC is suitable for most indoor applications, if the conductors won’t run in conduits, plenum-rated cable is required within ducts, plenums, and other spaces used for environments air. Polyethylene is recommended for outdoor applications.
The NEC has a number of coaxial cable listings that correspond to the particular jacketing material of the coaxial cable. A cable marked with the CATV listing is suitable for almost any location, except air handling plenums or building risers. In this case, the initials are an acronym for Community Antenna Television, and not cable television. The CATVP designation refers to use in a plenum or space with environmental air. CATVR has a riser-rated jacket. CATVX is allowed only in dwellings and inside raceways. However, many coaxial cables are rated for multiple uses, such as CATV and CATVR.
First and foremost, follow all requirements of the National Electrical Code for inside buildings and the National Electrical Safety Code for outside work. Outdoor installations require special techniques to allow the cable to withstand harsh environments.