System Troubleshooting for

Transcription

1 System Troubleshooting for Brought to You by Presented by Part 1 of 4 MARCH B1

2 System Troubleshooting for Part 1of 4 Taming Video System Trouble Spots Wouldn t it be nice if electronic security systems functioned trouble-free until obsolescence began to set in? As you will see, there are too many variables for that to happen.this series of articles has been designed to help technicians get past their fears and master the fine art of system troubleshooting. By Bob Wimmer Principal Video Security Consultants cctvbob@aol.com AT A GLANCE Troubleshooting electronic systems requires knowing how to define, isolate and repair problem areas More than half of all system problems are due to issues with cabling, cable connectors or cable installation Common faults include wrong type of cable, connector errantly installed, excessive force used during cable pull or exceeding cable s bend radius Best connector type is the threepiece BNC, which is the most reliable if it is installed correctly In video security systems, the higher the resistance of a single video loop, the greater the signal loss Welcome to the latest of Security Sales & Integration s acclaimed D.U.M.I.E.S. series: System Troubleshooting for D.U.M.I.E.S. Brought to you by Pelco, this four-part series has been designed to help educate readers on the fine art of video surveillance system troubleshooting. If you ll recall, D.U.M.I.E.S. stands for dealers, users, managers, installers, engineers and salespeople. This series will explain the different methods used to define, isolate and repair problem areas found in the CCTV security arena. Some basic knowledge of simple electronic theory will be helpful during these series of articles. However, for those who have no or limited knowledge of electronic theory, the material will be presented in such a way as to make the learning curve as painless as possible. Numbers Show Cable Main Culprit To start, let s look at a few basic statistics on the problems found in system installations. It is a known fact that 65 percent of most problems found are associated with cabling, connectors and connections, and cable-installation methods. The next area, which makes up approximately 27 percent, is related to excessive input power, insufficient AC equipment power and an excessive temperature environment. The last major area, at about 7 percent, is problems created by system-installation personnel, including incorrect camera setups, improper system termination and improper B2 MARCH 2006

3 setup of on-screen equipment menus. The remaining 1 percent is due to actual equipment failures. Key Questions for System Analysis Troubleshooting any system is an art form. Having the ability to ask the right questions and then be able to reconstruct the facts can be a challenge. Asking the right questions is critical for good system analysis. The first question to ask, and usually the most difficult to correctly interpret the response, is: Has anyone tried to fix this problem before me? Electronics, for the most part, are logical in design, while most people s reaction to analyzing a problem is NOT. If the answer to this question is yes, then conducting a factory default of all associated equipment is your first choice of action. Remember, however, that if the equipment offers no backup storage method, a complete manual programming sequence may be required once the factory default is enabled. Depending on the complexity of the equipment, this could be very timeconsuming. If there is no factory default setting, another common practice is to adjust all setup and service controls to midrange, which is usually the starting point used by most equipment manufacturers. Once you have established that no one tried to correct the problem before you arrived on the scene, the next group of questions will follow the detailed list at right. Following the stated guideline that 65 percent of problems are related to the type of cable, connectors and cable installation methods, the next questions should be: 2. What type of coaxial cable was installed (material)? 3. When were the cables installed (time)? 4. Who installed or pulled the cables (person)? Cabling is the lifeline for any surveillance system. Whether it is a standard video coaxial cable, shielded twisted pair for data, Cat-5e for unshielded twisted pair (UTP) equipment or Cat-5e for networking, all must follow the guidelines set up by this industry. When it comes to coaxial video cable, for many, cable is just cable. However, this is not quite true. Although the same number or name may refer to each type of cable, they may use different materials in their construction. It is this difference in materials that can affect the system s performance. Baseband/Composite Vs. RF Video In a CCTV surveillance system, the signal transmitted by the camera equipment is known as a baseband or composite type of signal. Even though it produces a standard video signal as found in today s non-high definition television sets, the actual video signal transmitted is slightly different and causes much confusion and problems in the security industry. Baseband or composite video is a raw signal consisting of video and color information, and vertical and horizontal synchronizing signals. Radio frequency (RF) has all of the same information found in a baseband signal with one exception: It is protected by a frequency shield. This shield protects the actual video data from outside sources, as well as provides a different means to distribute the signal. Answer Me These 7 Questions Those differences require different material in the cable s construction. Baseband or composite video cable requires a center conductor made of copper (solid or stranded), 75-ohm impedance and an overall shield constructed of copper. In an RF video cable, the center conductor is again made of copper, and the overall impedance is also 75 ohms. However, the cable s shielding is made out of aluminum, NOT copper. Looking at Mistake Causes, Results The main reason for most misuses of coaxial cable is fairly simple cost! Aluminum-shielded cable is less expensive then cable made with copper shielding. A quick comparison shows that aluminum-shielded cable is half the cost of copper-shielded cable. In a large application, the cost can be substantial. But why is there confusion? The most common reference for standard coax cable is RG-59U RG stands for radio guide; 59 indicates the impedance and center conductor sizing; and U indicates multiple uses. It does not indicate the type of shielding used, and this is why there is confusion. As for the results of these errors, we must first remember that an RF-video signal is protected by an RF shell and, therefore, signals, such as the vertical 1. Has anyone tried to fix this problem before me? 2. What type of cabling is installed? 3. When were the cables installed? 4. Who pulled the cables? 5. How long are the cable runs? 6. Are pull boxes and/or conduits installed? 7. Are there video amplifiers in the system? Asking the right questions is critical for good system analysis. MARCH B3

4 System Troubleshooting for and horizontal sync pulses, are not directly affected by the cable type. Whereas in CCTV, being a raw video signal, the entire signal is dependent on the cabling material. In a nutshell, the frequencies of vertical and horizontal synchronization are ~60Hz and ~15,750Hz, which actually places them within the audio frequency range. The frequency range of coax using aluminum shielding is 50MHz and greater. This mismatch of frequency creates problems like poor, or in some cases, no video images. As we incorporate more and more digital equipment into this industry, the requirement for more stable and distortion-free signals will become a must. When Were the Cables Installed? This question of when cabling was installed may appear to be unnecessary, especially if you installed and are maintaining the system. However, for those who were not involved with the original installation or are just entering a location for the first time, this knowledge can save a lot of troubleshooting time and effort. If the system was just installed, a few more questions should be considered. They are: How long are the cable runs? Who pulled the cables? Recommended cable lengths used in the CCTV industry vary. The old table for cable distance went something like this: RG-59U... 1,000 feet RG-6U... 1,500 feet RG-11U... 2,000 feet These numbers do not take into consideration how many splices (if any) there are within the run, the amount of looping devices in a system and how hard the cables were pulled during installation. Here are a few tips for installing coaxial cable: First and foremost, follow all National Electrical Code (NEC) requirements when installing coaxial cables. Distribute the pulling tension evenly over the cable, and do not exceed the minimum bend radius*. Exceeding the maximum pulling tension or the minimum bend radius of a cable can cause permanent damage, both mechanically and electrically, to the cable. * - Bend radius = the minimum curvature one can bend a cable without causing damage. A single cable with shielding = 10 to 12 times the overall cable diameter. (NEC , Conductor Bending Radius) When pulling cable through conduit, clean and deburr the conduit completely and use proper lubricants in long runs. With more digital equipment being incorporated in the security industry and with this equipment requiring higher video signal levels at the receiving end, the new recommended cable distances read something like this: 75-ohm impedance Copper center conduction Copper shield RG-59U feet RG-6U... 1,000 feet RG-11U... 1,500 feet What does all this have to do with troubleshooting? A great deal! The odds are if the cable was just installed, either the cable distance is too great, the wrong type of cable was installed, the connector was errantly installed, excessive force was used during the pulling of the cable or someone exceeded the cable s bend radius. All of these result in weak or distorted video signals. On the other hand, if it turns out the cable has been installed for a long period of time, the odds are there are corrosion or moisture problems with the cabling network. This again requires more questions. Comparison of Composite Vs. RF Video Cabling 75-ohm impedance Copper center conduction Aluminum shield CCTV only RF only Radio frequency (RF) cabling has all of the same information found in a baseband or composite signal with one exception: It is protected by an aluminum frequency shield. Weak or Distorted Video Flowchart Incorrect cable New installation Check Excessive cable length Problem corrected Poor connection installation Weak/Distorted video Corrosion Existing installation Check Problem corrected Cable breakdown Whether an installation is new or existing determines the troubleshooting strategy a technician needs to follow. B4 MARCH 2006

5 Are pull boxes and/or conduit installed? Are there video amplifiers used in the system? In many applications, conduit is required to meet the local standards for fire prevention. Many think just because conduit is being incorporated that they do not have to concern themselves with special types of cable jackets or environmental conditions, especially for underground applications. Wrong! It is unlikely you would ever find an underground conduit that remains dry for any length of time. For the most part, within a few weeks moisture already surrounds the outer jacket of the installed cabling. With the addition of mechanical splices within a system, corrosion can also play a very important part in loss of video as well as data-signal strength. Setting Up Testing Parameters We now know the possible causes of cable failures. Some will be manmade, some due to the breakdown of cable construction, while the corrosive force of moisture will lead to others. Armed with this knowledge, we may formally begin the troubleshooting process. But in a troubleshooting environment, how can anyone determine the quality of the video cable installed in the system? Any system using coaxial cable for the video signal can be checked. Many manufacturers offer special testing equipment known as time domain reflectometers (TDRs), which have been around for many years and remain the fastest, most accurate way to pinpoint cabling problems. TDRs are used to locate and identify faults in all types of coax. They can isolate major or minor cabling problems, including sheath faults; broken conductors; water damage; loose connectors; crimps; cuts; smashed cables; and shorted conductors and system components. In addition, TDRs can be used to test reels of cable for shipping damage, cable shortages, cable usage and inventory management. Principles of Operating a TDR TDRs work on the same principle as radar. A pulse of energy is transmitted down a cable, and when that pulse reaches the end of the cable or a fault along the way, part or all of the pulse energy is reflected back to the instrument. The TDR measures the time it takes for the signal to travel down the cable, see the problem and reflect back. It then converts this time to distance and displays the information as a waveform and/or distance reading. The problem with TDR units is they can be costly, varying from a few hundred dollars to in excess of $1,000, depending on the features. For most of us, this price usually far exceeds the budget for the year. The following method is a much less expensive and simpler solution to using a TDR. It may not pinpoint the exact problem location, but it can get close. The coaxial cable required in a CCTV application is made up of a copper center and copper shielding. All wire, including copper, has resistance. 4 Steps of 3-Piece BNC Connector Assembly 1. Strip cable as detailed on connector package. Place ferrule on cable jacket. 2. Solder or crimp center pin on center conductor. 3. Insert connector onto cable and slide ferrule against connector. 4. Crimp ferrule using proper crimping tool. 4 Steps of 2-Piece BNC Connector Assembly 1. Strip cables as detailed on connector package. Place ferrule on cable jacket. 2. Twist connector onto center conductor. 3. Slide ferrule against connector. 4. Crimp ferrule using proper crimping tool. MARCH B5

6 System Troubleshooting for Therefore, we can use this information to check the quality of most systems. Boning Up on Electronic Basics In addition to wire, all components have resistance, which is the opposite of current. In short, the more resistance you have in a circuit, the greater the loss. In the case of a video security system, the higher the resistance of a single video loop, the greater the signal loss. When this loss reaches certain levels, the amount of signal left may be insufficient to properly reproduce a video image on a monitor s screen. If this theory sounds a bit confusing, let s try another way to explain resistance and resistive loss in a video cable. Take for example a standard garden watering hose. Once connected to a water facet, the hose acts as a pipeline to transport the water to another location; in this case a watering bucket. If this same hose generates a leak, some of that water no longer reaches the bucket. If more and more leaks occur, eventually little or no water will reach the bucket. Now consider each leak in the hose as a resistive value. The more leaks (ohms) within a cable, the less water (signal) will reach the bucket (monitor). To summarize, the greater the resistance found in a video cable, the poorer the image quality. So what can cause excessive loop resistance? 1. Exceeding normal cable distances 2. Wrong selection of video cable 3. Wrong type of shielding material 4. Improper connector installation 5. Corrosion of splices within the cable run 6. Breakdown of cable material over time We have already discussed most of the problems that can cause excessive direct current (DC) resistance in a video system. However, there are additional concerns that must be addressed. The first one that comes to mind is connectors. Are all connectors acceptable in the CCTV industry? Which connectors are better? What is the proper method for connector installation? Using BNC Connectors for CCTV Short for Bayonet Neill Concelman (named after its inventors), BNC connectors are used with coaxial cable such as RG-59 and RG-6 A/U. However, there are numerous alternate definitions of the BNC acronym, including barrel nut connector, Bayonet nipple connector, Bayonet navy connector, baby N connector, British naval connector and British national connector. By any name, the basic BNC features male-type connectors mounted at each end of a cable. This connector has a center pin attached to the center cable conductor and a metal tube fastened to the outer cable shield. A rotating ring outside the tube locks the cable to any female connector. The best connector type is the threepiece BNC, which is the most reliable if it is installed correctly. The next connector on the list for reliability is the two-piece BNC connector. The last Diagnosing a Shorted Wire and most dangerous to any CCTV system is the twist-on BNC connector. Although no major equipment manufacturers recommend twist-on connectors, they are nevertheless being widely installed. The people who use them say they are easy and less expensive than two- or threepiece connectors. However, for the most part, twiston connectors are actually more expensive and iffy at best for performance. Studies show the normal life of a twist-on is less than two years. Resolving Issues With Resistance So far, our discussion has focused on the video s lifeline: coaxial cable. With 65 percent of problems stemming from this area, a great deal of time was required to explain all the relevant issues. As mentioned, everything has resistance, and we need to check the This depicts a simple test using an ohm meter to determine the overall loss of a system s video signal due to the resistance found within the video cable structure. B6 MARCH 2006

7 resistance value of our overall video loop. This concept will play a very important part in our first troubleshooting procedure. Most installers rely on manufacturers recommended cable distances. But those distances are determined only by using a high-grade, coppercenter conductor (not copper-covered steel) and do not take corrosion, splicing, pinched cables, etc. into consideration. In a working system, technicians must understand and relate to all of those problems in order to troubleshoot and repair any surveillance system. The figure below depicts a simple test to determine the overall loss of a system s video signal due to the resistance found within the video cable structure. Some may term this as a cable compliance test. Use the following test procedure: 1. Remove the BNC connection from the output of the camera. 2. Short the center conductor of the cable to the shield or ground of the connector. 3. Locate the other end of the cable under test and remove it from the equipment (monitor, switcher, DVR, etc.). Video Resistive Loss Diagram 4. Connect a standard ohm meter to the circuit (black test lead to the shield of the connector, red lead to the center pin of the connector). 5. Check the DC resistance value on the meter. The maximum DC resistance of this cable assembly should be between 10 to 15 ohms. This indicates the resistance loss by the cable, any resistance loss due to connector or splice points, and any breakdown of the copper components of the coaxial cable. This is the maximum resistance that should be between the camera and monitoring location. If a lesser value were found, it would be to your advantage. (Note: DC-resistive value has decreased during the past few years due to the introduction of digital processed equipment such as multiplexers, DVRs and NVRs into the security industry. The main reason is digital equipment usually requires greater video signal strength than analog equipment.) With this test, installation and service technicians will no longer have to guess on the quality or length of the coaxial cable of the system. This is also especially a good reference point if problems occur after a few months of system operation. For the more advanced troubleshooter, this test does not indicate any system bandwidth or interference problems. It only measures the DCresistance loss of the circuit. You re Already Halfway Home With more than half of all problems generated by cabling, it is a great place to start troubleshooting. If care is taken upon initial installation, many of these difficulties can be avoided. The procedures described within these pages will not always find every problem area, but they can point service personnel in the right direction. Armed with an inexpensive volt-ohm meter and some basic knowledge, system troubleshooting can be less of a nightmare for technicians. Part 2 in this series will tackle the No. 1 problem confronting today s security technicians: system termination. Robert (Bob) Wimmer, a member of SSI Hall of Fame, is president of Video Security Consultants and has more than 34 years of experience in CCTV. His consulting firm is noted for technical training, system design, technical support and overall system troubleshooting. Resistance of center + splice + resistance of center Short End Test End Total Resistance = 10 to 15 ohms Resistance of shield + splice + resistance of shield The maximum DC resistance of the cable assembly depicted here should be between 10 to 15 ohms. This indicates the resistance loss by the cable, any resistance loss due to connector or splice points, and any breakdown of the copper components of the coaxial cable. MARCH B7

8 Reader Service Card No. 156