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How to Plan and Design a Digital CCTV System

Digital CCTV is offering integrators new and seemingly limitless design choices. Effective system planning means understanding your customer's needs as well as the characteristics of the interlocking equipment. Asking the right questions and truly listening to your customers is essential.

Digital CCTV is here to stay. The introduction of the first digital signal processing (DSP) cameras and advancing digital technology has thrown the entire CCTV network into a major tailspin.

The basic theory, glossary of terms and many installation procedures have changed to meet this growing digital demand. However, the basic design of any CCTV system has remained the same. Digital technology may sound confusing, but understanding a few buzzwords will help in overcoming the fear of the digital revolution. This article kicks off a special, six-part series on the world of digital CCTV by focusing on the planning and design stage - typically the most critical part of any project.

Understanding your customers' needs as well as the characteristics of the interlocking equipment is essential. Ask questions, talk to your customers; try to completely understand their concerns and security needs. However, in the final stage, you are the expert and should make all recommendations concerning the system layout and connectivity.

Good Planning Is Based on Asking Good Questions

When planning any security system, a few important questions must be answered so the customer as well as the system integrator can discuss all available options. The questions may seem to be very simple or foolish in nature, however, they relate to the type of equipment required, or the type of special digital features that may enhance the security system.
To start, the word digital, when used in most CCTV cameras, only means that the camera incorporates digital enhancement for the video signal processing. These cameras offer improved image quality as well as added features (such as backlight compensation, CCD iris control, electronic zoom and electronic sensitivity) to overcome problems associated with certain applications.

However, remember one thing: the output from 95 percent of all surveillance cameras is still analog. The reason lies in the required maximum operating distance needed in surveillance systems. A truly digital output camera would have a very limited operating distance (usually less than 50 feet), which would not be very useful in CCTV. As we turn toward networked cameras and system networking equipment, this limitation will begin to change.

Degree of Protection Determines Equipment

The degree of protection will determine the use of fixed-positioned cameras, remote positioning equipment, or a combination of both. A camera location that uses a pan/tilt or scanning device offers a lower degree of protection. To improve the degree of protection, integration of different systems may be useful. The overall application or purpose of the system will also determine the degree of protection required. As a rule, the greater the degree of protection, the greater the complexity of the system design, as well as the cost.

New System Applications Are Emerging All the Time

For many, understanding the application or needs of customers can be very difficult. The number of cameras required, the purpose of each camera, the type of switching system, the method selected to transmit the signals, how to display the information and the type of permanent storage devices can confuse even the best of us.

Applications can range from a single remote-view camera location to a 64- to 256-camera, multiplexed system with digital storage. Regardless of the system's simplicity or complexity, incorporating digital features can enhance each design.
One of the major improvements in using digital signal processing (DSP) cameras is that of backlight compensation (BLC). BLC allows for cameras to be aimed at exits or entrances, loading-dock doors, ATMs or underground parking facilities without the effects of extreme shading or silhouetting.

Another advantage, which is often overlooked, is the reduction in equipment size when converting to digital.
Applications involving color have also increased with the development of digital video processing cameras. The need for additional lighting and increased image quality, which has plagued the CCTV industry, has been greatly improved.

With Camera Positioning, Location Is Everything

The last phase in the planning stage should be determining the location of the equipment. This area is not just limited to the camera site. It should also encompass the monitoring location. With advanced digital camera features, once-forbidden areas of surveillance are now available. Locating camera equipment has become much easier. But let's not forget that the age of digital equipment also brings some new areas of concern.

Outdoor Design Takes More Time Than Indoor

Systems are divided into two major sections: indoors or outdoors. For the most part, indoor applications require less design time than outdoors. Reasons for this settle around the need for environmental enclosures to protect the equipment and the requirement for auto-iris lens assemblies.

However, the incorporation of DSP can greatly enhance many indoor and outdoor applications, which were limited by older camera designs. The need for improved image quality by both the end user and today's digital recording systems is essential for any successful surveillance system. Benchmarks in signal-to-noise ratios, improved BLC, and automatic gain features (AGC) are just a few of the improvements delivered by digital processed cameras. One of the major concerns for any outdoor application is how well the camera equipment will perform during low or poor light applications. This is one area in which DSP camera assemblies excel.

Addressing the 3 Major Design Variables

When starting any system design, a number of questions should come to mind. This list of questions can quickly be reduced once the application is determined -- reverting back to the planning stage of our system. The design stage is broken down into three major parts: camera equipment, communications and switching/display/storage.

Matching Cameras to Lighting Is Essential

We can compare CCTV to photography. In fact, CCTV is nothing more than electronic photography and follows basically the same rules.
Rule No. 1: The more light available, the less sensitive the camera has to be.
Rule No. 2: Matching lighting parameters with camera parameters can enhance image quality.
Rule No. 3: Cameras use reflected light to produce images. No matter how sophisticated the controlling system, transmission system or display and recording system, the total picture quality of any video surveillance system starts with the camera and lens. With this in mind, the first question for design should be, how much available light does the camera require to produce an acceptable video image?

What is electronic shuttering of cameras? In older CCD camera designs, an auto-iris lens was required to produce proper video output levels. The reason was the circuitry of those older chip camera imagers were always at full power or full sensitivity, which made the lens the controlling factor for the video output.

While most camera systems can produce satisfactory images with enough light, the selection of matching lighting characteristics can enhance many of today's CCTV systems. The advantages of matching a camera to lighting characteristics can be easily recognized, especially when installing color cameras in outdoor applications.

Black-and-White Cameras Not Picky About Lighting

In a black-and-white (B/W) camera system, almost all forms of lighting can be used, even infrared (IR), which can be used to enhance performance. Light sources such as mercury vapor, low- and high-pressure sodium and tungsten have been widely used for B/W camera applications.

With color systems, a few more considerations must be taken into account. First, all color cameras have a restricted light bandwidth. This bandwidth is between 400 nanometers and 790 nanometers, or the visible light spectrum. Because of this limited bandwidth, color cameras cannot be used with IR light sources (the IR range is between 800nm to 1,200nm) unless they incorporate automatic conversion from color to B/W, which is a new feature added by the use of digital technology.

Accurate Imaging Trickier With Color Cameras

Color camera designs offer more challenges to system integrators than those of B/W system installations. Since color cameras are sensitive to the color temperature of light as well as the color-rendering index (CRI) of light sources, understanding these effects will enable the designer to make more intelligent decisions.

CRI Affected by Different Types of Lighting

To fully understand what is meant by CRI, let's look at an example. If I view a green object and the light source was sunlight, that object would appear green. If I now view that same object using high pressure (HP) sodium lamps for illumination, that object would appear to be bluish in color. Certain types of light sources are better than others in reproducing color. Incandescent or tungsten, as an example, matches true sunlight in producing true color rendition; however, the operating cost of tungsten for exterior lighting is very expensive.

White Balance Offsets Lamp Temperatures

The overall color accuracy of the system also depends on the color of the light source. The white light from different light sources can range from a dull red through a bluish-white. This characteristic depends on the temperature (degrees Kelvin) to which the lamp is heated.

Different forms of lighting produce different ranges of white light. Because of these differences, a color camera must also have the ability to automatically compensate for these changes. This compensation, known as the white balance of the camera, is required to produce the proper color reference on the monitor.

When in Doubt, Use More Than Recommended Light

Camera systems use the light that is reflected from objects in order to reproduce an image. This reflection factor changes from application to application and plays a major part in the camera design. All manufacturers publish specifications for each of their camera products. These data sheets list the sensitivity of a product and, since the main design parameter in camera selection is sensitivity, it is very helpful to understand the guidelines used for measuring this sensitivity.

Rule of thumb: if the scene application is not snow, more light is required to produce the desired results stated on a manufacturer's camera data sheet. How much more light can be calculated, but a quick guideline is that for every 35-point difference from a manufacturer's reflectance factor, the available light should double.

Communication Methods on Tap for Next Session

As mentioned, the output of a DSP camera is still analog; however, transmission methods are also changing. The use of digital transmission is on the rise. Systems are now incorporating fiber optics, network wiring (UTP) or the Internet.
Design selections are based on operating distances, number of channels, system compatibility and cost. Which method is right for your application will be the topic in next month's issue.

As with any industry, the need to completely, understand the design characteristics and system components is essential for proper operation. The basic blocks of most systems are the same. Equipment selection becomes even more important as the age of digital technology and improved video features play a more important role in the CCTV industry.

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