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bleshooting abilities. While trouble- shooting any system can prove very frus- trating and time-consuming, having the wherewithal to ask the right questions and properly reconstruct the facts is the ticket to solving such problems as effi - ciently and painlessly as possible. 7 KEY QUESTIONS SIMPLIFY PROCESS In order to troubleshoot any system one must be able to analyze video images, incorporate the appropriate testing pro- cedures and then resolve the problem. It sounds quite simple; however, in most cases analyzing the problem can prove to be a challenge. Making the wrong de- cision can result in many hours or even days of chasing down the problem area. A few basic questions can lead you down the correct path of problem-solv- ing. T ese questions include: 1. Is the system new or old (how old)? 2. When does the problem occur (day/night)? 3. Type of transmission method (coaxial, UTP, fi ber)? 4. Any conduit (underground)? 5. Conditioned power (yes/no)? 6. Interference (constant or intermittent)? 7. Color of interference (gray/black/ white)? T e answers to each of these ques- tions will provide a link to logical trou- bleshooting procedures. Using the di- vide-and-conquer method should get the technician onto the correct path. Let's dig in by analyzing problems found in today's video industry. T e following sections present fi ve actual system problems encountered in the fi eld and explanations of how they were rectifi ed. CASE NO. 1: A METHODICAL APPROACH Looking at Figure 1, we can assume the camera has power and that video is con- nected. T e problem area seems to be a distorted video signal. T e fi rst question Figure 1: Distorted Signal tive path formed by the shield of the video cable and the chassis of the video equipment. With this information, the next question that should be answered is: What type of transmission method is installed? If the answer is coaxial cable or pas- should be about the age of the system. Is this a newly installed system or has it been in operation; if so, how long? In this situation, the system has just been installed. With that information, the next set of questions should include: how many distorted areas are present on the video image and what method is being used to transmit the video signal? T e fi rst part of that question may seem a bit strange; however, there is a little trick to determine the type of distortion. It is to count of areas of distortion (if that is possible) and multiply that number by 30. T e results will give you an idea of the type and frequency of the injected distortion. In this case, you can see two areas of distortion, and 2 X 30 = 60. T us, the in- terference is likely a 60Hz problem. One of the most frequent problems in new installations is what is known as a ground loop. T is is caused by a po- tential problem between two diff er- ent grounding points to a system. According to Ohm's law if you Areas of Distortion 2 X 30 = 60Hz problem Ground loops, caused by a potential be- tween two different grounding points, are a frequent problem in new installations. have resistance and current you will get a voltage. A ground loop is just that, it is an AC current that rides along with a video signal. It occurs on the conduc- sive UTP (unshielded twisted pair), then the logical conclusion would be a ground loop problem. If the answer is active UTP or fi ber optics, a ground loop may not be the problem. T e fi nal procedure to ensure the problem is a ground loop can be accom- plished in several ways. A ground loop can occur at various diff erent points throughout a system, such as from the camera to a monitor, camera to a switch- er or a control system to a DVR. Any time a system is referenced to a grounding point, a ground loop can be generated. T e following basic tests can be de- ployed to verify a ground loop before purchasing additional equipment. TEST PROCEDURE NO. 1: USING A STANDARD VOLT-OHM METER Ground Loop Test Using Volt-Ohm Meter Video cable Shield Equipment ground AC volt meter should not exceed 0.1VAC As mentioned, Ohm's law explains why ground loops occur and this same theo- ry can be used to verify such a condition. A standard volt-ohm meter (VOM) can accurately measure the problem voltage. First, disconnect the video connector from one end of the video loop. Place the positive and negative leads of the me- ter between the shield of the BNC con- nector and the chassis ground of the end equipment. T e meter should be set on AC voltage. A reading of 0.1VAC or great- er indicates the presence of a ground loop; if no voltage, then no ground loop. OCTOBER 2012 / SECURITYSALES.COM / A3 ss1012dumies.indd A3 9/26/12 1:45 PM