CCTV Basics

Select below:

The Camera
Cameras convert the visible scene captured by a lens into an electric signal and transmit that signal to a
monitor for viewing.

Several considerations should be taken into account when choosing the proper camera/lens for any video system:
• The purpose of the video system (detection, assessment, identification, ect.)
• The overall sensitivity of the camera needed based upon the actual application
• The amount and varying levels of light available at the scene
• The environment in which the camera will operate (indoors/outdoors)
• The field of view (FOV) required by the application (see figure 3)
• The lens
• Cost

Figure 3: Field of view.

Camera performance depends largely upon the reflected light at the scene and the quality of the cameras imager (see figure 4).

Where the level of available light can change dramatically, a camera equipped with automatic iris control can help assure consistent image quality. Automatic iris control enables cameras to open or close an auto iris lens to adjust the amount of light passing through the lens. On a bright, sunny day, for example, an auto iris camera will close the lens' iris to prevent strong light from reaching the camera's imager. At night, the camera will open the iris to allow a greater amount of light into the camera.

Cameras are available in various "formats" expressed as1/2, 1/3, or1/4 inches. These measurements represent the overall usable size of the camera's imager. In general, you should match the camera's format to the lens format. For example, a half-inch camera should be paired with a half-inch lens.

Today, thanks to design improvements, high quality images are possible with smaller formats.

Fixed and PTZ Cameras(see our PTZ selection)
CCTV cameras can be fixed or have pan, tilt and zoom (PTZ) capability. Fixed cameras are mounted on a fixed bracket and cannot move in response to operator commands. PTZ cameras are motor driven and can pan left and right, tilt up and down and zoom in and out for close-up or wide-angle viewing. (See figure 5)

PTZ camera.

A cameras housing protects the camera and lens from vandalism and the environment. It also can enhance the appearance of the camera installation and conceal the equipment from casual observation. All outdoor cameras require a housing of some type. The National Electrical Manufacturers Association (NEMA) rates housings on their ability to withstand environmental conditions. Protection from cold, heat, dust, dirt or other elements is needed to ensure optimum performance and extend the life of the camera.

Dome Cameras
Many PTZ cameras today are disguised in dark colored Plexiglas housings called domes. Dome cameras are found practically every major department store and in many industrial/commercial locations, hospital, colleges and government facilities (See figure 6). They are particularly popular wherever aesthetics are valued.

Dome cameras provide three primary benefits: 1) Deterrence Domes make it virtually impossible for suspects to determine where the camera is pointed. Individuals planning to commit criminal activity are unable to detect whether or not they are under active
surveillance.
2) Economy Domes equipped with a camera, lens, and pan/tilt unit can be augmented with "drones" that have the same outward appearance, but have no equipment inside. The result is more apparent camera coverage with a much lower system expense.
3) Aesthetic Appearance An exposed camera, lens, pan/tilt unit and associated wires are
unsightly. A dome makes the collection of equipment more aesthetically acceptable, and does not detract from the interior design of a retail or business office environment.

Placing a mirrored finished or smoked bubble around the dome can conceal a dome camera further.

However, when this is done, the bubble has the effect of sunglasses, reducing the amount of light reaching the lens and affecting the color accuracy picked up by the camera.

Dome cameras.

 
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VIDEO TRANSMISSION METHOD:   A mechanical adjustment in a camera that moves the imaging device relative to the lens to compensate for different back focal lengths of lenses. This is important when a zoom lens is fitted.
 
The choice of transmission medium depends on factors such as distance, environment, cost and facility layout. In addition, nearly all methods of transmission suffer from various forms of interference or loss. The essence of good design is to minimize this impact. Examples of current video transmission mediums include:

Coaxial Cable
A coaxial cable is one that provides a continuous physical connection - or closed circuit - between
the camera and the monitor (see figure 11). The cable is shielded to minimize interference from any nearby electronic devices or electrical wires. Copper braided coaxial cable is recommended to maximize conductivity and minimize potential interference. For traditional CCTV systems, as well as many applications today, this is the most common and economical method of signal transmission over relatively short distances.

Fiber Optics
Fiber optic technology changes an electronic video signal into pulsed or laser light and injects (transmits) it into one end of a glass rod (the fiber optic cable). At the other end, a receiver translates the pulsed light back into an electronic signal capable of being displayed on a monitor. The transmission is unaffected by any kind of interference, water in conduit or high voltage being run in the same conduit. Fiber optic cables have a large signal capacity (bandwidth) and no possibility of a spark from a broken fiber. Hence, there is no fire hazard to a facility even in the most flammable environment. Fiber optics offers a cost-effective method of sending large transmissions over long distances.

Telephone Line
A telephone line is a standard twisted pair of wires that can transmit the image for distances up to one kilometer without video signal boosting. This dedicated line connects the transmitter (camera end) with a receiver (monitor end). Through the use of specialized transmission and receiver equipment, it is
possible to use standard telephone lines for video signal transmission.

Microwave
If already in place, microwave can be a very efficient and cost-effective method of delivering black & white or color video. Microwave turns the video and data signals into high radio frequency signals and transmits them from one point to another via free air and space. A receiver then converts the transmission back into the video and data signals and displays the scene on a monitor. Good quality transmission can be achieved over a line of sight path (see figure 12). Microwave technology offers a large bandwidth to carry video, however, it can be affected by environmental conditions. It is a practical option when a wire path between the camera and monitor locations cannot be established or is prohibitively expensive. Microwave transmission is regulated by the FCC, and a license is required.

Radio Frequency
Radio frequency (RF) is a reliable, but short distance, line-of-sight video transmission technology. It is becoming increasingly popular where hardwiring methods are either impossible or impractical, and has been used successfully to reduce cabling costs even within large buildings. Environmental conditions or other RF in the area can affect it.

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The Peripherals
As the number of cameras and monitors increase, simple system designs eventually give way to more complex designs that require peripheral components. These peripheral components may include switchers, VCRs, multiplexers, quad splitters, video printers and time date generators.

Switchers
A video switcher enables different cameras to be switched to different call-up monitors. In a smaller, cost-conscious application, a manual switcher allows users to select the camera they want to see by pressing a button associated with the camera

The most popular type of switcher, a sequential switcher, contains circuitry that will switch one camera to another automatically. The operator can set the length of time (dwell time) that a scene remains on the monitor before sequencing automatically to the next camera. This allows operators to keep tabs on numerous cameras with only one monitor, but also creates a drawback known as "switcher dilemma."

To illustrate switcher dilemma, imagine a system with eight cameras, each programmed to switch after "dwelling" on the monitor for five seconds. In this scenario, a considerable gap will occur between the time the first image is displayed and the time the eighth image is displayed. If the dwell time is shortened, operators may not be able to assimilate each camera image before it switches. The situation worsens when recording the video for review at a later time. On playback, you may see a door opening on camera 1, then suddenly see the video switch to camera 2, followed by camera 3, camera 4, and so on. By the time camera 1 appears again, the door is closed, and you are left wondering who came through the door while cameras 2 through 8 were flashing sequentially on the monitor.

Switcher dilemma can be solved with more sophisticated switchers, more operators or an alarm feature that will display video image automatically when an alarm point is activated.

Matrix Switcher
A matrix switcher is a more complex design enabling the user to switch any video signal to any call-up monitor in a large-scale system. They normally incorporate P/T/Z control and other features such as presets and alarm inputs/outputs.

Multiplexers
Unlike conventional recording systems, a video multiplexer collects full-screen pictures from up to 16 cameras and displays them simultaneously on a monitor .

Operators have the option of displaying any camera full-screen or multiple cameras in reduced size.

Multiplexers also can record all cameras in the system onto a single videotape. The cameras are recorded sequentially at a high rate of speed. As mentioned earlier, a standard video signal is comprised of 30 separate frames each second. In a video system containing 15 cameras, the multiplexer selects two frames from each camera and records them to a single videotape. The result is an effective frame rate of 2 frames per second, instead of the standard 30.

Most multiplexers today contain a motion detection feature that enables the system to record more frames of video from cameras showing motion than from those not showing any motion. The multiplexer does this by reallocating frames from one camera to another as needed. The net result is higher quality recordings of scenes that are more likely to be important to security personnel.

When a time lapse VCR is used with a multiplexer, the recording mode should be as short as possible to reduce the number of seconds required to record all cameras (remember, cameras are recorded sequentially) (see figure 16).

This is why it is a great advantage to use hi-density or virtual real-time TLR's when using multiplexers. Virtual real-time VCRs record 4 times the frames per second of conventional time-lapse VCRs.

Figure 16: The VCR, working with a multiplexer and several cameras,
recordsfewer frames per second in time-lapse mode.

One of the strongest advantages of using multiplexers is that during playback, the multiplexer decodes the tape allowing investigators to display only selected frames with the same address. This pullout feature saves investigators hours of time reviewing recorded actions. Another advantage is that during playback, any desired camera can be displayed full-screen.

Multiplexers offer system administrators an effective means of managing multi-camera surveillance systems:
• With the high-speed switching technique, multiplexers offer maximum coverage of all cameras
without the gaps created by sequential switchers
• Multiplexers may be able to reduce CCTV costs by reducing the number of monitors, VCRs,
and videotapes needed
• The number of tapes needed for video storage may be reduced
• Savings in space, heat, power, and ventilation also may be possible

Quad Splitters
The main feature of a quad splitter is the ability to compress images from four separate cameras and simultaneously display them on a single monitor screen. When four cameras are displayed, each occupies a quarter of the screen. A single camera can be selected and displayed full-screen, as well.

Unlike multiplexer recording, quad splitter recording yields only what appears on the monitor screen. If the VCR is recording a four-camera display, then playback will show four cameras.

Recording CCTV
Most CCTV systems use VCRs to record video images from the dedicated and/or call-up/switchable monitors (see figure 18). Recordings make it possible to view events that may have gone unnoticed at the time they occurred or that may require close scrutiny later. Technological advances now make it possible to record images in digital form on a computer disk. While this technology shows great
promise for the near future, VCRs presently are the most prevalent recording method.

VCRs designed for CCTV can record video images in either real-time or time-lapse modes. In the real-time recording mode, the tape moves at the same speed as home VCRs (2 to 6 hours) and captures 30 pictures per second. This produces high quality recordings, but requires operators to change tapes every two to six hours. The 24-hour real time VCR will record 24 hours of video on a single tape at 20 pictures per second.

It is considered a real time recorder because 20 pictures per second approximates the ability of the human eye to easily distinguish moving images.

Time-lapse recording makes it possible to record video over long periods of time on a relatively small amount of videotape. Time-lapse recording can capture from 12 to 960 hours of video on one T-120 tape. However, the number of pictures recorded per second in time-lapse mode decreases significantly as the recording time increases. As fewer pictures are recorded per second, critical images may not appear on tape, and movement (e.g. a car traveling across a parking lot) may appear jerky .

Note:Fewer pictures are recorded when using time-lapse mode, causing motion to
appear jerky. Notice how cars "disappear" when fewer frames per second are recorded.

The seconds per picture and number of pictures per second rendered by various time- lapse VCR recording modes are shown in the next table:

 

Recording mode	Seconds/pictures	Pictures/second
2 hr.	.0333	30
6 hr.	.0333	30
12 hr.	.1	10
24 hr.	.2	5
48 hr.	.4166	2.4
72 hr.	.625	1.6
96 hr.	.8333	1.2
120 hr.	1	1
240 hr.	2	.5
480 hr.	4	.25
960 hr.	8	.125

Another way to capture video on tape is through alarm recording. With this method, the VCR usually runs in time-lapse mode until an alarm occurs. The VCR then switches from time-lapse mode to real time mode, capturing video images at a rate of 30 pictures per second. After the alarm resets, the VCR returns to time-lapse mode to conserve tape. The CCTV system will need an alarm switching mechanism in order to perform this function.

When a time-lapse recording is played back at normal playback speed, the playback will present events at a speed faster than real time. It is common to play back a time-lapse recording in real time mode to speed the time necessary to review the tape. If necessary, the tape can be slowed to review those events that require greater attention.

Digital Recording
A more recently developed method of recording video images is that of Digital Recording

Digital recorders compress and store images to a computer hard drive using various compression techniques. These techniques include JPEG, MPEG, Wavelet and a host of other proprietary methods. Images can be stored at a rate of 20 frames per second (fps) to as many as 480fps depending on the software features offered by the manufacturer.

Operating systems offered by manufacturers vary from Linux to Unix to Windows based systems. Although Windows is the most user friendly and familiar system, it tends to be less stable than it's lesser-known counterparts.

Archived recording time varies depending on the size hard drive in the recorder. Hard drive sizes range from 0 (external only) to 400gb internally with option of raid storage for virtually infinite capacity. Hard drive size should be considered conjunctively with the time period necessary to archive.

Many Digital Recorders incorporate multiplexing with inputs varying from 4, 9, 16 and as many as 32 inputs. Similar to the conventional multiplexer/VCR setup, the frame rate will be divided among the cameras being recorded. However, unlike conventional methods, each camera input of a digital recorder can be programmed to record more or less frames per second depending on camera priority (Ex: camera #1 = 10fps, camera # 2 = 5fps, camera # 3 = 12fps, camera # 4 = 3fps using a 4 input recorder with maximum 30fps).

Another very distinct advantage to digital recording is the ease of locating events. No more fast- forward and rewind. Just type in a time, date and camera number and you can playback instant images.

Other options available with DVRs include motion detection, remote viewing via LAN, WAN, or Internet, on board media such as CD Rom, DAT storage or removable hard drives, SCSI and USB ports as well as remote control of pan-tilt devices and the list grows everyday!

Work with your VSS sales representative to determine which digital product is best for your application.

Video Printer
A video printer produces a hard copy printout of any live or recorded video scene, using thermal or other sensitized paper. The "still" photo can be used for multiple purposes, such as providing suspect identification to police agencies, alerting employees to safety hazards, etc. Photo printers are available in black & white or color.

Figure 21: A photo printer.

Time Date Generator (TDG)
A Time and Date Generator can annotate the video scene with chronological information. Also, a camera identifier is placed on the monitor screen to identify the camera scene being displayed. Today, most VCRs, multiplexers and camera controllers have this function built into the product.

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THE MONITOR
The Monitor
The monitor receives the transmitted electronic video signal from the camera and paints it across a
cathode ray tube (CRT) to display an image to a viewer. Although similar in function to a TV set, a CCTV monitor provides higher lines of resolution (better picture quality) and accepts only video signals rather than RF/antenna signals.

Lines of resolution refers to the total number of horizontal lines the camera or monitor is able to
reproduce. The more lines on a screen, the better or sharper the video picture will appear. CCTV
monitors can provide up to 1000 lines of resolution compared to an average of 300 lines provided by television sets.

Several factors can affect the monitoring function: Size of the monitor (9" and 14" are popular sizes), its positioning and angle relative to where the viewer sits, the quantity of monitors, and the quality (resolution) of the monitor itself (see figure 13). In all cases, sufficient growth must be factored into any console design. It's also important to note that all monitors generate heat. Whether on a table or enclosed in a console, be sure to provide adequate ventilation and air-conditioning.

Most CCTV systems use both dedicated monitors and call-up, or switchable, monitors. A dedicated monitor displays the video from only one camera. A call-up, or switchable, monitor enables operators to "call or switch" different cameras to the monitor. Generally, call-up/switchable monitors are larger than dedicated monitors and give operators the ability to view multiple images simultaneously (multiplexed) as well as scrutinize the camera image more closely.

There are many different monitor sizes available. When choosing the proper size of monitor, you must first determine the distance of the monitor in relationship to the user. Also determine the quantity of cameras to be displayed on a given monitor simultaneously (multiplexed).

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