The electronic monitoring system is designed to work continuously for 24 hours, and the installation quality at the end user will directly affect the running performance and life of the system. Therefore, we must pay attention to the following basic requirements for monitoring system installation. 1, surge suppression/line protection It is a common feature of all successful systems to configure surge protectors at the power input of the system. Although many security systems use UPS, it should be noted that not all UPS have built-in surge protection. Similarly, video and data lines need to be protected. 2. Cable quality Another issue worthy of attention is the quality of CCTV coaxial cable. RG59U, RG6 and RG 1 1 all require 100% copper core and 95% copper braided shield. The maximum resistance of line loop connection shall not exceed 15 ohm. 3. Proper grounding of the grounding ring circuit can minimize the influence of the grounding ring circuit. The voltage difference between different grounding shall not exceed 100mVAC (measure the voltage difference between the disconnected coaxial cable and shielding layer and the BNC grounding terminal behind the equipment). 4. Interference /EMI and RFI exposure to any interference environment will reduce the video quality and affect the overall performance of the system and product reliability. Avoid exposing the equipment to large motors such as elevators, water pumps, fluorescent columns, and various high-power radio equipment. 5. Control the working environment of the equipment. The equipment of the safety system shall be installed in a clean air-conditioned room and on the standard rack of 19 ". Appropriate space should be left between the equipment, and forced ventilation fans should be used. 6, the correct backup steps of digital video recorder If the hard disk video recorder is sent for maintenance or upgrade, it is possible to lose all the information in the original program and hard disk. Its maintenance center cannot guarantee that these data can be recovered. Hard disk backup is the responsibility of every user. Here, we recommend that users back up their hard disks regularly. Please make all users clearly aware of the potential problems that may be caused by not backing up. If one or more of the above basic principles are not strictly observed, the integrity of the monitoring system will be threatened. Correct installation will ensure the normal operation of the system and increase the trust of users. It is important that the product warranty only applies to the product under the correct installation conditions.
3. After a monitoring system enters the debugging stage, trial operation stage and delivery, there may be such faults, either it can't run normally or the system can't meet the technical indicators required by the design; Or the overall performance quality is not ideal, and some so-called "soft defects" appear. These problems are inevitable for a monitoring project, especially for a complex large-scale monitoring project. After these problems appear, it is the duty and responsibility of engineers and technicians to try to solve them. In the monitoring system, problems often occur during debugging and trial operation. Generally speaking, the system that has been put into trial operation and accepted for delivery should not have problems in a short time. Even if there is a problem with the system put into use, it often occurs in the equipment or construction quality (especially the construction quality of the transmission part). The following are some common faults for readers' reference.
I. Faults caused or reflected by equipment and components and their solutions
Before the equipment (or components) is installed, commissioning and power-on test shall be carried out as required. However, due to some reasons in the installation process, it is also common that equipment (or components) have problems.
A. equipment failure caused by wrong power supply. There are several possibilities for incorrect power supply: incorrect power supply line or voltage, insufficient power (or insufficient line diameter of a power supply line, excessive voltage drop, etc.). ), short circuit, open circuit and instantaneous overvoltage in the transmission line of power supply system. In particular, equipment damage caused by power supply error or instantaneous overvoltage occurs from time to time.
B, due to some lines, especially the lines connected to the equipment, not handled well, resulting in open circuit, short circuit, poor insulation between lines, wiring errors, etc. , the equipment (or parts) is damaged, the performance is degraded or the equipment itself is not damaged, but the phenomenon reflected is on the equipment or parts. Because some devices (such as three-variable lens, camera of pan/tilt) have many connections, they are often not handled well, and the above problems will occur. In particular, poor quality of some connectors and poor wiring technology are the common causes of problems. In this case, we should calmly analyze the fault phenomenon and judge which lines in several lines have connection problems to produce that fault phenomenon. This will narrow down the problem. For example, in a camera with three variable lenses, the image signal is normal, but the lenses can't be controlled, so there is no need to check the video output line, just the lens control line. In addition, connectors, especially BNC connectors, require very high welding technology and connection and installation technology for video cables. If it is not handled properly, even if there is no problem during debugging and trial operation, problems will occur after running for a period of time. In particular, it is very common for cameras with pan/tilt to lose connection due to long-term omni-directional movement. Therefore, in this case, special attention should be paid to the connection of equipment and various lines to meet the requirements of long-term operation.
C. quality problems of equipment or parts themselves. Generally speaking, carefully selected commercial equipment or components should have no quality problems. Even if there is a problem, it often happens after the system has been delivered for a long time.
In addition to the product quality problems mentioned above, the most common problems are caused by improper adjustment of equipment. For example, the adjustment of the camera's back intercept is a very detailed and accurate work. If not carefully adjusted, there will be problems such as poor focus or defocus during various operations of the three variable lenses. In addition, whether the positions of some switches and adjusting knobs on the camera are correct, whether they meet the technical requirements of the system, and whether the encoder switches or other adjustable parts of the decoder are set correctly will directly affect the normal use of the equipment itself or the normal performance of the whole system.
D. Problems caused by incorrect connection between equipment (or parts) and equipment (or parts). Problems in this regard generally appear in the following aspects:
A. Impedance mismatch If the video is connected to a high-impedance display, the image will be bright, the characters will shake or sometimes characters will appear.
B, communication interface or communication mode is wrong. This situation often occurs between the control host and devices with communication control relationship such as decoder or control keyboard. This is mostly because the selected control host and decoder or control keyboard are not the products of the same manufacturer. Generally speaking, different manufacturers adopt different communication methods or transmit different control codes. Therefore, the host, decoder and control keyboard should all be made by the same manufacturer.
C. The driving capacity is insufficient or exceeds the specified number of equipment connections. For example, the number of main control keyboards and auxiliary control keys corresponding to the control host is specified. Exceeding the specified number will cause the system to work abnormally. If the power supply for the translation/tilt of the decoder is lower than the actual translation/tilt, the translation/tilt cannot be driven.
Second, the transmission system fault analysis and solutions
The transmission system of TV monitoring is usually based on video transmission. Limited by space, the following only analyzes the faults in video transmission mode and puts forward some solutions.
First, the most common fault phenomenon in video transmission is 50-week power frequency interference. A black or white bar appears on the monitor screen and slowly scrolls up or down. This phenomenon is mostly caused by 50-cycle power frequency interference (AC interference) caused by grounding fault in the system. It should be mentioned that sometimes, due to the poor performance (or partial damage) of the power supply of the camera or the control host (matrix switch), this fault phenomenon (sometimes two black bars or white bars appear) will occur. Therefore, when analyzing this fault phenomenon, we should distinguish two different fault causes.
A simple way to distinguish between power supply problems and ground loop problems is to connect only one camera without power supply problems to the control host. If the above interference phenomenon does not appear on the display, there is no problem with the control host. Next, you can connect a portable monitor to the video output end of the nearby front-end camera, and check the cameras one by one to see if any cameras are disturbed by power problems. If there is, it will be handled. If not, the interference is caused by other reasons such as grounding circuit.
B, there is wood grain interference on the display. The appearance of this kind of interference will not slightly drown the normal image, but in severe cases, it will be impossible to watch the image (or even destroy the synchronization). There are many complicated reasons for this failure. Generally speaking, there are the following reasons: the quality of video transmission line is not good, especially the shielding performance is poor (the shielding screen is not a copper screen with good quality, or it is too thin to shield). At the same time, the line resistance of this video line is too large, which leads to a large signal attenuation and aggravates the fault. In addition, the characteristic impedance of this video cable is not 75 Ω, and the distribution parameters are not in line with the specifications, which is also one of the reasons for the failure.
It is difficult to judge the cause of this fault, and it is difficult to solve it by replacing the wiring because the construction has been completed (wiring has been completed). Therefore, it is necessary to ensure the selection of video cables that meet the standards and requirements in advance. Don't buy a poor quality video cable just to save money, otherwise there will be endless troubles. Because the above interference phenomenon is not necessarily a fault caused by poor video line, the judgment should be accurate and cautious. Only by excluding other possibilities can we consider it from the perspective of bad video lines. The method of judgment is to send the remaining video line (if there is no remaining video line, we will intercept a section of this line in the system) to the detection department for detection after eliminating other possible causes of this fault. When the test result is unqualified, it can be determined that it is a cable quality problem. If it is really a cable quality problem, of course, the best way is to replace all these cables and replace them with cables that meet the requirements. This is the best way to solve the problem completely. When the interference is not serious, we can try to supply power to the whole system by purifying the power supply and connecting UPS online, which can often reduce or basically eliminate the interference. However, due to the different spatial signal conditions around the system, this method sometimes has no obvious effect, or sometimes it is effective and sometimes it is ineffective. Because the power of the power supply system is not "clean". The power supply here is not "clean", which means that the interference signal is superimposed on the normal power supply (50-cycle sine wave). The interference signal on the power supply mainly comes from the equipment using SCR in the power grid. Especially the SCR equipment with high current and high voltage, the pollution to the power grid is very serious, resulting in the power supply of the same power grid is not "clean". For example, there are high-power SCR frequency modulation and speed regulation devices, SCR rectifier devices, SCR AC /DC conversion devices and so on. In this power grid, it will pollute the power supply. The solution to this situation is relatively simple, as long as the whole system adopts purified power supply or online UPS power supply, it can basically be solved.
There are strong interference sources near system C. This can be judged by investigation. If this is the case, the solution is to strengthen the shielding of the camera and ground the pipeline of the video line. C. Fault caused by short circuit or open circuit between video cable core and shielding net. The performance of this fault is that there is deep and chaotic moire interference in a large area on the display, which destroys all the images and does not form images and synchronization signals. This often happens on BNC interfaces or other types of video interfaces. As long as these connectors are carefully checked one by one, the problem can be solved.
This kind of fault phenomenon is also easy to judge, that is, when this kind of fault phenomenon occurs, it is often not the signal of the whole system that is faulty, but only those signals with bad joints.
D. Fault phenomenon caused by mismatch of transmission line characteristic impedance. The manifestation of this phenomenon is the interference of several vertical bars with equal spacing on the monitor screen, and the frequency of the interference signal is basically an integer multiple of the line frequency. This is because the characteristic impedance of the video transmission line is not 75 Ω, resulting in impedance mismatch. If you watch the waveform of the disturbed image with an oscilloscope, you will find that a high-amplitude harmonic oscillation waveform is superimposed on the back shoulder of the line synchronization head, which is the reason for the interference. Through the analysis of waveform and the quantitative measurement of video cable, it will be found that the distribution parameters of this kind of video cable with unsatisfactory impedance are not ideal, which is actually one of the reasons for impedance mismatch. Therefore, it can also be said that this interference phenomenon is caused by the fact that the characteristic reactance and distribution parameters of the video cable do not meet the requirements. The solution to this problem generally depends on the method of "series resistance at the beginning" or "parallel resistance at the end". It is worth noting that in the case of short video transmission distance (generally within 150m), the above interference phenomenon may not necessarily occur when using the video cable with mismatched impedance and too large distribution parameters. Therefore, in systems with large transmission distances, we should not be confused by short-range interference when analyzing this fault phenomenon.
The fundamental way to solve the above problems is to ensure the quality when purchasing video cables. When necessary, the cable shall be sampled and tested.
E. space radiation interference caused by transmission lines. This interference phenomenon is mostly caused by the strong high frequency space radiation source near the transmission system, the front end of the system or the central control room. One of the ways to solve this situation is to understand the surrounding environment and try to avoid or stay away from the radiation source when the system is established; Another method is to strengthen the shielding of the front-end and central equipment when the radiation source cannot be avoided, and the transmission line is made of steel pipe and grounded.
Third, other failures.
First, the Yuntai fault. It is a common fault of tripod head that it doesn't work well or doesn't turn at all after being used for a long time. Apart from the factors of product quality, this situation is mainly caused by the following reasons:
Only the camera is allowed to be installed (i.e. the camera sits above the turntable), and it is used in a lifting mode (i.e. the camera is installed below the turntable). In this case, the lifting mode will increase the operating load of the pan/tilt, so the transmission mechanism of the pan/tilt will be damaged or even burned soon after use.
Motor.
The total weight of the camera and its protective cover exceeds the bearing capacity of the tripod head. Especially for outdoor use, the weight of the protective cover is often too large, which often leads to the problem that the platform cannot turn (especially in the vertical direction). Outdoor pan/tilt is out of order or even damaged due to too high or too low ambient temperature and inadequate waterproof and antifreezing measures.
B. When the distance is too far, the keyboard cannot remotely control the camera (including the lens) and the pan/tilt through the decoder. This is mainly because the control signal is too attenuated when the distance is too far, and the control signal received by the decoder is too weak. At this time, it is necessary to install a relay box at a certain distance to amplify the shaping control signal.
C, display image contrast is too small, the image is bright. This phenomenon is either the problem of the control host and the display itself, or the transmission distance is too long or the video transmission line is too attenuated. In this case, line amplification and compensation devices should be added.
D, the image clarity is not high, the details are lost, and in severe cases, the color signal is lost or the color saturation is too small. This is because the high-frequency loss of image signals is so great that the signals with frequencies above 3MHz are basically lost. In this case, the transmission distance is too long, and there is no amplification compensation device in the middle; Or the distributed capacitance of the video transmission cable is too large; Or the concentrated distribution of equivalent capacitance between the core wire and the shielding wire of the transmission line in the transmission link.
E, tone distortion. This is a common fault phenomenon in long-distance video baseband transmission mode. The main reason is that the high frequency phase shift of the signal caused by the transmission line is too large. In this case, a phase compensator should be added.
F, operating keyboard failure. This phenomenon can basically be determined to be caused by the "crash" of the operating keyboard when there is no problem with the connection. There are generally methods to solve the "crash" in keyboard operation description, such as "resetting the whole machine", which can be solved by this method. If it cannot be solved, the keyboard itself may be damaged.
G, the host switch to the mirror is not clean. The performance of this fault phenomenon is that the interference of other pictures or the interference of line synchronization signals of other images is superimposed on the selected picture. This is because the quality of the host's matrix switch is too poor to meet the requirements of isolation between mirrors. If RF transmission system is used, it may also be caused by excessive cross modulation and mutual modulation of the system.
The large TV monitoring system associated with burglar alarm is a high-tech complex system. Although there may be various failures, as long as the quality of the selected equipment and equipment is well controlled and the construction is carried out in strict accordance with standards and specifications, there will generally be no major problems. Even if there is a problem, as long as you calmly analyze and think, "suit the right medicine" and don't blindly disassemble it, you can solve the problem soon.
H, poor communication failure
Sometimes the controlled pan/tilt or electric lens can move normally, sometimes it can't move (or delay), or it can't stop after the action. The main reason is that there is something wrong with the communication line. Check the matching resistance (120Ω) of the RS-485 communication terminal on the decoder when the wiring is correct. Or disconnect the host interface and the farthest matching resistor, measure the DC resistance RD of the terminal pin of a single communication chip and the DC resistance R2 of the communication port of the whole system with a multimeter, and compare with the theoretical calculation (R2=R0/n, where n is the number of decoders connected in parallel in the whole system). If the difference is too large, it can be considered that there is something wrong with the communication chip, and the problematic chip can be found by point-by-point elimination. If there are multiple branches in the communication line, each branch can be disconnected to determine the approximate range of communication failure.