KISS and choose.
CHOOSING THE PROPER CLOSED-CIRCUIT TELEVISION (CCTV) system may seem like a dilemma. However, with the KISS method (keep it simple, stupid) you can find answers to your major questions about equipment and installations as you go along. Fortunately CCTV systems are not as complicated as they appear.
Rule number one is to keep your system in perspective. A CCTV system contains only three major components. The first component is a camera, the second is cable, and the third is the monitor. Any other item you may use in your system is a peripheral piece. For example, if a camera must view more than one area, a pan or pan/tilt unit and controller are needed. Since the camera produces a picture without this equipment, the pan or pan/tilt and controller are considered peripherals.
To design and apply a CCTV system properly, you must take seven steps before ordering bids or equipment. They are as follows:
* Determine the purpose of the proposed CCTV system.
* Define the areas to be viewed by each camera.
* Choose the proper lens for each camera.
* Determine where the monitor or monitors for viewing the system will be located.
* Determine the best method for transmitting the video signal from the camera to the monitor.
* Lay out the control area and determine what enhancements are needed.
* Choose the equipment based on the system layout notes. To narrow the scope of discussion, this article will concentrate on the first three steps alone. If you construct a checklist for each step, your final choices for cameras, housings, and lenses will be simple.
STEP ONE IS TO DETERMINE THE purpose of the proposed CCTV system. If the purpose is to monitor the back aisle of a store, little advance layout is necessary to make a viable system. If the intention is to cover several locations in a complex or several complexes, a singular definition of each camera's location should be written before quotes, bids, or system layouts are presented.
Remember, CCTV systems are not security by themselves. Cameras cannot respond to alarms, put out fires, or call for help. Camera systems cannot prevent entry to a building, nor can they rock a restless baby to sleep. Camera systems do allow security personnel to monitor several points from a single location. They can alert a viewer to a potential problem in the back confines of a building, and they can allow a mother to monitor the sleeping baby from another location in the home. CCTV systems are an enhancement to existing security measures.
Properly defining the purpose of each camera includes weighing the security risk of each area to be viewed. If a high-security area is to be viewed, it may be worthwhile to interface the CCTV system with an alarm device such as a door contact, microwave motion detector, photo beam, or video motion detector. If a camera is installed in a low-security area, alarm interfacing may not be necessary. Recording the video signal as a backup reference may be the best option.
Before choosing a camera, you must decide whether the camera's primary duty is to watch for security breaches, safety hazards, injured personnel, or vehicles. Also, will the camera be used to identify personnel entering or leaving a secured area? In defining the areas to be viewed, you may find a need for added security measures, such as alarm monitoring, patrols, locks, barriers, or access control.
Another question is whether the unit should be visible or covert. Camera visibility can prevent certain nonchalant crimes in shopping centers or malls.
Covert cameras, on the other hand, often promote security while allowing individuals to be comfortable in their surroundings. If covert applications are to be used, the security manager must make sure to respect privacy rights.
For example, a major clothing store was having a sale on swimsuits. The management was concerned that people were slipping the suits on in the changing rooms and then concealing them under their street clothing. A new executive wanted to mount covert cameras in each of the changing rooms, allowing the store's employees to monitor the customers as they tried on various pieces of clothing. The management did have a legitimate security concern but could not use CCTV to monitor the changing rooms. Similar situations happen every day, and every day lawsuits are filed because a person's right to privacy has been stepped on.
STEP TWO IS TO DEFINE THE AREAS to be viewed by each camera. Since cameras vary in size, light sensitivity, resolution, type (tube or chip), and power, it is essential to determine where a camera is to be mounted before choosing one.
Several factors must be considered for each location. As for light, is the lighting in the area bright or dim? Is it constant or variable? Does the location contain lights that could brighten the scene at night or during cloudy days? Does the viewing area contain main windows? Are the windows covered with heavy curtains, which are closed during the day, or are they opened according to the varying light conditions outside? Will the proposed scene have a bright background that silhouettes the people being monitored? If so, would additional lighting from the same direction as the camera improve the camera's view?
If additional lighting is necessary for nighttime operation, can visible lighting be added or would it be more cost-effective to use covert infrared lighting? Many cameras view infrared (IR) light as humans view visible light. If the decor of a building or the presence of neighbors forbids the installation of pole-mounted or building-mounted security lighting, consider IR lighting. It can usually be installed cheaply at the site of the camera.
Another factor is the environment. If the camera is inside, does it need to be protected from vandals or customers? Interior camera housings are available in configurations ranging from ceiling mounts (designed to mount in place of ceiling tiles) to overhead bubbles to corner-mount stainless steel or bronze housings.
Must the camera housing blend in with existing decor? Is the environment extremely dirty, average, or very clean? Excessive dirt or dust buildup in the camera causes the unit to run hot and may cut back its performance or life span.
If the camera is to be mounted outside, you should ask the same questions but also consider temperature. If winter temperatures in your locale drop below 35 [degrees]F, the camera's protective housing will need a heater. Although most tube cameras generate enough heat to perform well in low temperatures and most charge-coupled device (CCD) cameras operate in temperatures below - 30 [degrees]F, lenses tend to slow down or freeze up completely in such temperatures. This freezing up is due to the type of grease used in the iris, focus, and zoom rings. If summer temperatures rise above 80 [degrees]F, tube cameras will need cooling fans, though many of the newer CCD cameras can operate in temperatures up to 145 [degrees]F.
If the unit is to be installed in the sun, a sunshade will be needed to prevent excessive heat buildup in the camera housing. If the unit is to be facing east or west, a sun visor may be needed to cut glare from the rising and setting sun to deter overheating.
What are the options for mounting a camera? That depends. Will the camera be mounted high in the air? If so, how can it be reached for maintenance? Will the camera's angle of view be so steep that only the top or back of heads will be visible? Will the unit be mounted under an overhang, next to a wall, or above major obstacles such as air conditioning units? If so, will there be enough room to open the housing from the top or will a bottom-hinged unit work better? Should the unit be mounted on a swing arm to allow easy access from a window on upper floors? If the unit is to be mounted in a ceiling tile housing, is there enough room above the false ceiling to install the housing?
Another location consideration concerns what each camera is required to view and from what distance. For proper security viewing, you should not depend on the camera to view more than two objectives (one major and one minor), and the camera should not pan (move side to side) more than 45[degrees] left or right from the center of its major focus. Good video surveillance is often waylaid by expecting too much from a single unit or installing fewer cameras than are actually needed. The object of the video system should be kept in the foreground at all times. The higher the security risk of the viewing area, the fewer the objects a camera should be required to watch. In high-security locations, it takes four cameras to view a 360 [degrees] area. Budgets, of course, may force a compromise.
Once the location, environment, and lighting for each area of the system have been determined, you can choose the class of camera that best suits your needs. Cameras come in two categories, tube and CCD. While tube cameras still have their place in the market, CCD or chip cameras are changing camera applications fast.
Tube cameras use image pickup tubes and require regular maintenance, including the replacement of the image tube itself. The strongest advantages of chip cameras are that they require less energy and take up less space (due to the lack of high-voltage image tubes), require less maintenance (average image chip life expectancy is five years, compared to the average image tube life of one to two years), and more flexible, coming with more standard features than tube cameras.
Chip cameras, however, also have problems. Many 2/3-in. and 1/3-in. chip cameras are so sensitive to IR lighting that they must use IR filters to enhance day pictures. Unfortunately, these IR filters hamper the cameras' sensitivity to lower light levels. If the IR filters are removed, the night picture improves but the day picture degrades. Hence, the user must decide which viewing time is more important, day or night.
Factor number one in choosing a camera is light. If the lighting in an area is bright and constant, a standard vidicon tube camera or a low-cost chip camera usually produces favorable results. If the light in an area is bright enough for you to read fine print in a magazine, it is usually bright enough for this type of camera. Vidicon cameras are usually inexpensive and require a fixed-iris or manual-iris lens.
Vidicon cameras have a high propensity to burn or retain images, meaning the pickup tube shows the scene it has been staring at even after the lens is capped. Burned images often are a hindrance to security and safety. If the camera is producing an image of the fixed surroundings, it is possible to miss new action.
For example, a standard vidicon camera is located inside an elevator and is under constant observation by the security personnel of the apartment complex where it is mounted. A woman enters the elevator and is beaten and robbed. When the video recording of the incident is played back in court, no evidence of the mugging appears, since the camera's tube had such a severely burned image of the interior of the elevator.
Chip cameras, on the other hand, have a low propensity to burn or retain images, and some are even warranted against such problems. Chip cameras can also be used in bright, constant lighting.
Another class of cameras is the low light variety. Ultricon and Newvicon tube cameras (trademarks of RCA/BURLE and Panasonic, respectively) are the most common cameras used over the past decade. Both types offer good viewing in areas where lighting is variable or low. Low light refers to a level below the human eye's comfort level but not below actual sight. Since these cameras are designed to work in low light, autoiris lenses must be used. Autoiris lenses contain built-in shutters that regulate incoming light based on the size of the video signal being produced by the camera.
Ultricon and special-order, red-level Newvicon cameras are also sensitive to IR light. IR light is not visible to the human eye, so it is considered covert lighting. Ultricon cameras generally have a higher sensitivity to IR light than Newvicon cameras unless the special red-level Newvicon tube is ordered.
IR light can be a major enhancement to any video system where standard or visible lighting is limited or too costly to install. For example, a city jail is required to maintain surveillance on prisoners to prevent them from committing suicide. Since the state also requires that each prisoner be allowed eight hours of darkness for sleeping, video surveillance becomes a problem. Low-level IR lighting, Ultricon, red-level Newvicon, or chip cameras can produce usable pictures of the cells in the dark.
The strongest advantage chip cameras offer over Ultricon and Newvicon cameras is their cost of maintenance. The average 2/3-in. Ultricon or Newvicon tube costs $200 to $300 and has a life expectancy of two years under good conditions. Chip cameras do not require biennial replacement of the imager and can save you money through lower maintenance requirements. Care should be taken, however, to respect the extra sensitivity of the Ultricon to lower light levels, and exact comparisons should be made before deciding on a type of camera. For long-range outdoor surveillance in low light, 1-in. Ultricon and Newvicon cameras have not yet been matched by CCD cameras.
The third class of cameras is the intensified variety. Until recently, intensified tube cameras were untouched by the chip cameras on the market. Intensified cameras are designed to work in extremely low light levels, such as those in back parking lots, along fence lines and in other outlying areas. Unfortunately, intensified cameras are the most misapplied cameras in the industry, being used in well-lit parking lots, street corners, and other areas where a less sensitive camera could easily be used.
Intensified tube cameras are known for their grainy pictures. Since these cameras are designed to work best in little or no light, day picture quality is compromised to ensure the best and strongest amplification of night light. The chip version of these cameras has started making its mark on the industry in the past year. Only a few intensified chip cameras on the market today match or outperform intensified tube cameras.
The greatest advantages intensified chip cameras have over their tube counterparts are in cost and life expectancy. An intensified tube camera costs from $2,000 to $6,500 and has a life expectancy of one year. The cost of such a camera with a lens and controller ranges between $12,000 and $20,000. By contrast, the average cost of a complete intensified chip camera is between $6,000 and $13,000, and the camera usually comes with a manufacturer warranty guaranteeing the chip for two to five years.
Great care must be taken when comparing chip to tube. Be sure to make apple-to-apple comparisons. This article speaks well of chip cameras, and the market is definitely going to drop tube cameras completely over the next few years. However, at the moment the tube is still alive and kicking. Don't be afraid to ask for side-by-side demonstrations when choosing between chip and tube cameras.
STEP THREE IS TO CHOOSE THE proper lens for the application. There are four considerations in choosing a proper lens: the format and class of the camera, the distance from the camera to the scene, the field of view desired, the iris, and whether the camera is black-and-white or color.
The first consideration is easy. The format of a camera is determined by the size of the usable image section that the lens focuses the light on. To illustrate, draw a circle (representing the front target area of a tube), then draw a rectangle in the circle and measure from the lower left corner of the rectangle to the upper right. This measurement is the format size of the tube you have drawn. Chip camera formats work the same way minus the circle.
The reason the format of the camera determines what lens to use relates to the focusing capabilities of the lens-to-camera relationship. If a smaller format lens is used with a larger format camera (for example, a 2/3-in. lens with a 1-in. camera), tunnel vision or a poorly focused picture results. On the flip side, a larger format lens may be used with a smaller format camera, (for example, a 1-in. format lens with a 2/3-in format camera). Thus a 1-in. camera requires a 1-in. lens, while a 2/3-in. camera works well with a 1-in. or a 2/3-in. lens.
The distance from the camera to the scene or scenes to be viewed determines what size of lens is needed. Lenses come in four configurations: telephoto, standard, wide angle, and zoom (combination of the first three).
The first three lenses mentioned (telephoto, standard, and wide angle) are fixed-focal-length lenses. Focal length is the distance from the surface of the lens to the point of focus and is measured in millimeters. Standard lenses reproduce pictures equivalent to what the human eye sees. Telephoto lenses act as telescopes producing pictures larger than what the eye sees. Wide-angle lenses produce pictures with great width, usually wider than the peripheral vision of the human eye. Larger mm numbers equate to telephoto lenses while smaller mm numbers equate to wide-angle lenses.
Each format size of camera has a different size (millimeter length) of lens as a standard. This is because of the difference in the image area of the tube or chip. For example, a 16 mm lens is the standard lens for all 2/3-in. cameras, while 24 mm lenses are the standard lenses for all 1-in cameras. Exhibit 1 lists the different lenses for different formats.
Another consideration is the field of view, which is the actual size of the scene that the camera will see with a specific lens at a specific distance. For example a 1-in. format camera with a 160 mm lens sees a scene 16 ft. wide and 12 ft. tall at a distance of 200 ft. The image has a depth of field that goes from 130 ft. to 220 ft. (Depth of field is the amount of the picture that will be in focus. In this example, any item closer to the camera than 130 ft. or farther away than 220 ft. is out of focus.)
With the use of simple math or a CCTV lens selection slide rule, you can calculate the lens focal length you need. The first step is to determine how much area is to be viewed by the camera. A rule of thumb is that the more the camera views, the less detail it picks up.
A simple procedure called the T method helps determine if a fixed-focal-length lens should be used or if a zoom lens would better suit the situation. (See Exhibit 2.) The T method involves drawing a horizontal line from the camera to the area to be viewed and a vertical line between the two farthest points of the scene to be viewed. If a single vertical line is drawn, a fixed-focal-length lens would work; if two or more vertical lines are drawn, a zoom lens would be better.
To determine what focal length is needed to view the desired field, see
Another rule of thumb about lenses is that the light available at the scene is the light available to the camera. The wider the lens is, the more available light from the scene is used by the camera. The longer the lens is, the less available light the camera has to operate with. Therefore, the longer the lens to be used, the more light-sensitive the camera's imager should be.
Another decision to make in determining the focal length of a lens reverts to the T method. If several scenes are to be viewed, a zoom lens is needed. Zoom lenses are measured in two focal lengths, representing the widest angle and the greatest telephoto effect of the lens. For instance, a 16 mm to 160 mm zoom lens ranges from a 16 mm wide-angle lens to a 160 mm telephoto lens. Zoom lenses should be kept within a 10:1 ratio for all 1-in. format cameras (both tube and chip) and within a 6:1 ratio for all 2/3-in. format cameras. A 10:1 ratio would mean, for example, a 16 mm to 160 mm lens.
The type of iris is another important consideration. The iris, which is the shutter of the lens, controls the amount of light allowed to pass through the lens to be focused on the tube or chip: Since vidicon cameras and their chip counterparts require full, constant light, a lens with a fixed or manual iris may be installed on these cameras. A fixed aperture or iris means the iris will not change the amount of light that passes through the lens. Manual iris lenses give the installer the option of setting the lens iris for the best picture under the available light.
Autoiris lenses work through a process known as video sampling. The video sampler that controls the iris of the lens is located either in the lens or in a separate controller. Video samplers control the opening of the iris in direct proportion to the voltage of the video output from the camera. Because the iris is a hole through which light and images pass, the opening must not become too small or the picture will be distorted.
For that reason, some lenses come equipped with an Intra-spot or eclipser filter mounted within them. (Intra-spot is a trademark of Vicon.) The purpose of the filters is to control the light without compromising the quality of the day picture. A lens with an Intra-spot or eclipser filter may have an iris setting equivalent of f/400, while its counterpart lens without the filter may have an f-stop rating of f/22. Intra-spot or eclipser lenses are a must with extremely light-sensitive cameras such as intensified tube or intensified chip cameras.
The last process in lens selection is to purchase color-corrected lenses for color cameras. A black-and-white lens mounted on a color camera produces poor picture definition and color.
Remember the KISS method. If you treat the task of choosing video equipment as a series of small steps, it is easy to design and implement a reliable, effective system.
Charlie R. Pierce is president of L.R.C. Electronics Company and L.T.C. Training Center, both in Davenport, IA. He is a member of ASIS.
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|Title Annotation:||Closed-Circuit Television; keep it simple, stupid|
|Author:||Pierce, Charlie R.|
|Date:||Nov 1, 1989|
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