CCTV VIDEO TRAINING MANUAL Someone once said, "Knowledge is the key to success". This rule also applies to the installation and maintenance of CCTV camera equipment. Have you ever installed a CCTV camera system and then had to go back to solve a problem that was overlooked. A basic understanding of CCTV video signals, can save you hundreds of man hours, improve customer relations and increase job profitability all at the same time.
Table of Contents VIDEO LEVELS. 1 HOW SYNC PULSE AMPLITUDE EFFECTS CCTV INSTALLATIONS. 1 WHITE LEVEL IRIS SETTING, HOW MUCH IS ENOUGH? 1-2 PEAK TO PEAK MEASUREMENT OF VIDEO. 2 COLOR CAMERAS AND COLOR BURST. 2 VERTICAL INTERVAL, ITS MANY USES. 2 TERMINATION, THE END OF THE LINE. 2-3 THE BASIC THREE. 3 CCTV VIDEO GROUND LOOP PROBLEMS. 3-5 CCTV FOCUS PROBLEM SOLVING. 5 DEPTH OF FIELD, WHAT IS IT? 6 THE PROBLEM WITH AUTO IRIS LENSES. 6-7 HOW TO SHOOT A LICENSE PLATE WITH A CCTV CAMERA.
VIDEO LEVELS. To discuss video let's start with the unit of measure, the I.R.E. unit. I.R.E. stands for Institute of Radio Engineers, this regulating body set the standards of measure for the video industry. This standard has been adopted by all industries in the United States and other parts of the world. 140 I.R.E. units is equal to 1 Volt Peak to Peak. I.R.E. units are easier to use because they divide into a video signal evenly. For example proper Sync on a camera is 40 I.R.E.
If you set the iris for more than 100 I.R.E. units, the picture can be washed out causing loss of picture definition. Some cameras can be set to 120 I.R.E. units, but it should be noted that the standard is 100 I.R.E. units and in any case all cameras in the system should be set to the same level of white. This will ensure that the white portion of the picture will be the same brightness when a monitor is switched between them. PEAK TO PEAK MEASUREMENT OF VIDEO.
Proper termination can be checked by measuring the SYNC pulse amplitude anywhere in the video cable. It should read 40 I.R.E. with the termination ON, and 80 I.R.E. with the termination OFF. If the SYNC level does not change when you remove the termination, the camera or video source is not standard 75 Ohms and should be serviced or replaced. Problems with V.I. control systems can result if the level does not double when you remove the termination. THE BASIC THREE.
Here is how the 60 cycle bar gets into your video picture. If you connect a coaxial cable to a monitor or other equipment that plugs into the 60 cycle main power and the other end of the coaxial cable becomes grounded locally for any reason a Ground Loop is created. Any difference in the 60 cycle voltage between these two ground points will create a current flow in the shield of the coax that induces the 60 cycle AC voltage into your video signal.
These transformers must be installed at the coaxial cable that is originating the 60 cycle bar problem. Isolation transformers only work when they can block the current flow in the shield. Once 60 cycle bars become part of the video signal, no economical down stream solution will remove the bars. Use a portable monitor to find the origin of the ground loop problem, start at the camera and move down the coaxial cable until you see the bars appear on the portable monitor.
DEPTH OF FIELD, WHAT IS IT? All lenses have a characteristic called Depth of Field. Depth of Field is a zone in front of the lens that is in focus. It is measured as the minimum distance and maximum distance from the lens where objects are in focus. All objects inside this minimum and maximum bracket zone will be in focus. The further away you go from this bracketed "in focus zone", either toward or away from the camera the more out of focus the objects become. THE PROBLEM WITH AUTO IRIS LENSES.
Hand held focus meters such as the CM-2 Camera Master are also useful in determining the maximum focus of any scene. They are more accurate than large screen monitors and much easier to take up a ladder. They display the maximum focus numerically on an LCD type display. By eliminating the subjective nature of focus setting, you will insure that all cameras will be set to their maximum focus by any installer.
HOW TO SHOOT A LICENSE PLATE WITH A CCTV CAMERA. When your customer asks you to set up a camera to grab a shot of a license plate on a car, here are a few things you will want to know. WHERE TO LOOK. When setting up a camera to view a license plate, the framing is very important. You must frame the camera so that the plate will be in the camera’s view no matter where the plate is mounted on the car, or how the car is positioned in the roadway.
This darkening effect is caused by the auto iris in the camera. When it sees the bright hot refection or headlights, the iris in the camera will close down the opening in the lens. An auto-iris takes the light that it sees and tries to determine how to set the opening in the lens for the best picture illumination. It can use a peek measure of the light level entering the lens, or when you engage the “Back Light” feature it will take an average of the light ignoring the hot spots.
HOW TO MEASURE CCTV CAMERA OUTPUT IMPEDANCE. The vast majority of coaxial cables are either 50 Ohm or 75 Ohm Characteristic Impedance. This Characteristic Impedance is determined by the ratio of the diameters of the shield and core wire and the Dielectric Constant of the insulating material between the core wire and the shield. The CCTV Industry chose to use the 75 Ohm standard for coaxial cable.
The key idea here is that such intermittent or failed conditions are caused by a CCTV camera with a zero output impedance, not a failure in the Pan and Tilt or other equipment. THE SOLUTION. Buy only CCTV cameras that exhibit 75 Ohm output impedance! But how can you be sure a particular camera really has 75 Ohm output impedance when the spec sheets for that camera proclaim 75 Ohms? The answer of course is to test the output impedance before installing them in the field.
DIGITAL VIDEO RECORDER PROBLEM SOLVING. The new digital revolution has brought us many new and exciting products for the CCTV industry. The DIGITAL VIDEO RECORDER or (DVR) may be one of the most important upgrades that can be made to any CCTV system. The DVR takes a camera video signal and converts it to a digital bit stream and saves it on a computer hard drive. It can then be played back with remarkable fidelity. This new technology brings with it a new set of problems and solutions.
The amount of headroom varies from one manufacturer to another, so you may discover one brand works better than another under certain circumstances, but the problem does not necessarily lie with the DVR. THE REAL PROBLEM. One of the most over looked problems in CCTV installation is the output level adjustment of the camera. The standard for camera output is SYNC = 40 I.R.E. units, WHITE = 100 I.R.E. units, and the COLORBURST = 40 I.R.E. units.
GB-60 GROUND LOOP BLOCKER AMPLIFIER HOW TO PREVENT LIGHTNING DAMAGE IN CCTV. Protecting a CCTV system and it components from lightning damage does not use the same methods used to protect human life from electrical shock. In fact many of the techniques used to protect humans from lightning also cause some other problems in the CCTV system. First of all, nothing can prevent a direct lightning strike. The result is usually a smoking melted down blob of carbon and metal.
Lighting Protection in the form of diode and gas tube lighting suppressors need to be installed at one end and maybe both ends of any long cable run. The long cable runs are more prone to voltage build ups due to local lightning static discharges. When lightning strikes from cloud to cloud or from the upper atmosphere to the ground, a differential charge appears on the ground.
This ground loop is created by the normal ground at the DVR or Monitor and the new ground applied by the lightning arrestors. This will look like black or translucent bars on the video image. These bars can stand still or move slowly up the screen. When the bars reach the top of the screen others will appear at the bottom of the screen to take their place. Since you cannot remove one of the grounds to eliminate the ground loop it may be necessary to install ground loop blockers to finish the system.
This 60 cycle line frequency is the common reference used to lock the cameras together. For this reason only AC powered camera's have the Line-Lock feature. DC powered camera's are not capable of being Line-Locked. When you select the Line-Lock feature in a camera there is internal circuitry that samples the 60 cycle AC frequency and uses it to time the Vertical Interval Pulses. All Line-Lock cameras have a Phase control that must be adjusted when the camera is installed.
In commercial buildings the utility power is Three Phase, that is three separate 60 cycle lines whose phase is 120 degrees apart. Moving the power line that your camera is on to a different phase will throw off the timing and require a readjustment of the phase control on the camera. If monitor personnel complain about picture roll, a fast check of timing can be made.
CCTV UPS TROUBLE SHOOTING TIPS. Many CCTV Closed Circuit Television systems use a UPS Un-interruptible Power Supply to provide guaranteed continuous power to operate a surveillance system. The UPS also provides down stream voltage regulation that protects equipment in the event of under or over voltage swings that occur during “brownouts” or brief power outages. The UPS will also protect equipment from voltage surges or spikes coming from the Main Power Line.
The “square-wave” type of UPS will put out the same 60Hertz frequency but its output waveform is that of a square-wave. A 60Hertz square-wave signal contains the “fundamental” or lowest frequency of 60Hertz, however it also has every “harmonic” or multiple of that frequency all the way up to and beyond the video frequency range. Strong high level signals in the Kilo-Hertz region (1000Hz) and even in the Mega-Hertz region (1000,000Hertz) will interfere directly with video.
TROUBLE SHOOTING. To begin trouble shooting you must first identify the source of the interference. First disconnect the suspected UPS and turn it off (power it down). This will guarantee that the UPS cannot create the interference in the first place. Then reconnect the equipment that was powered by the UPS to a normal non UPS power line. Check the monitor and see if the interference has been eliminated. This test will check for direct camera power supply and ground loop type interference at the same time.
The term, Lines of Definition actually refers to the number of times the picture screen can be modulated (made lighter and darker) across the screen. Therefore a test pattern for this purpose would display vertical lines on the screen of the Monitor. Fifty white lines alternating with fifty black vertical lines across the screen would constitute a total of 100 Lines of Definition. The more lines that can be discerned, the greater the fine detail observable in the picture.
If it is a Tape Recorder, old or worn tape will play back fewer "Lines" than new tape. Even new tape of different types may show variation in the number of "Lines" played back. Worn Tape Heads will also show fewer "Lines" than new Tape Heads. It is recommended that this test be performed at regular intervals to catch Tape Head wear before performance suffers.
Even greater distances of 8000' or even 12000' can be equalized by adding intermediate "booster" amplifiers and equalizers. These cable equalizer/amplifiers are made by a variety of manufacturers, and when included in CCTV system designs can completely offset the cable or twisted pair loss so that the resultant "Lines" delivered are as good as the Camera, Recorder, and Monitor can produce "on the bench".
Using the VLTG-800 Video Line Test Generator as a test signal source and the CM-1 Camera Master as the picture quality measurement system enables a specific quality Proof of Performance to be performed on any new transmission. Component parts can be evaluated as to picture quality to isolate, identify, and replace non-conforming parts to upgrade CCTV system performance.
HOW FIBER SYSTEMS WORK: To understand the problem it will help you to know how a video fiber optic transmitter and receiver work. When you connect your video signal onto the fiber transmitter that signal is first put through a buffer amplifier to control the input impedance and then the video signal is clamped to the tip of White, the most positive part of the video signal.
If the input video signal deviates from the established standards, the tip of white clamp will change the relationships within the video signal according to how much the video input level is off of the standard level. The standard level expected by the fiber equipment is 140 I.R.E. units, specifically 100 I.R.E. units of White (Luminance) and 40 I.R.E. units of Sync Pulse (Synchronization Pulse).
There is another condition that can occur that will have devastating effects on a fiber systems output. This problem is one that affects older established systems, if the system was working and begins to cause problems, look at the levels at the output of the fiber system. If the Sync signal is unusually high (over 50 I.R.E. units) it may be possible that the internal 75 Ohm termination has been damaged by a lightning storm or other high voltage ground-loop related occurrence.
