1. Faults caused by or reflected by equipment and components and their solutions
Before installing the equipment (or components), debugging, power-on experiments, etc. should be carried out as required. But despite this, it is common for equipment (or components) to have problems due to some reason during the installation process.
A. Equipment failure caused by incorrect power supply. Incorrect power supply generally has the following possibilities: incorrect power supply line or power supply voltage, insufficient power (or insufficient wire diameter of a certain power supply line, excessive voltage reduction, etc.), short circuit, open circuit, or instantaneous overload in the transmission line of the power supply system. Wait. In particular, equipment damage due to power supply errors or instantaneous overvoltage often occurs.
B. Due to poor handling of certain lines, especially the lines connected to the equipment, open circuits, short circuits, poor insulation between lines, miswiring, etc. result in damage to the equipment (or components) and performance degradation. Or the equipment itself is not damaged, but the phenomenon reflected is caused by the equipment or components. Because some equipment (such as cameras with three variable lenses and pan/tilts) have many connections, which are often not handled properly, the above problems will occur. In particular, the poor quality of some connectors and poor wiring workmanship are common causes of problems. In this case, a calm analysis should be carried out based on the fault phenomenon to determine which of the lines have connection problems that caused the fault phenomenon. This will reduce the scope of the problem. For example, if the image signal of a camera with three variable lenses is normal, but the lens cannot be controlled, there is no need to check the video output line, but only the lens control line. In addition, connectors, especially BNC connectors, have very high requirements for welding processes and video cable connection and installation processes. If not handled properly, even if there are no problems during the debugging and trial operation stages, problems will occur after a period of operation. It is particularly worth pointing out that due to the omnidirectional movement of cameras with pan/tilts, it is common for the cables to fall off and break over time. Therefore, special attention should be paid to the connection between the equipment and various lines in this case to meet the requirements for long-term operation.
C. Quality problems with the equipment or components themselves. Generally speaking, commercialized equipment or components that have been carefully selected should not have quality problems. Even when problems do occur, they tend to occur after the system has been delivered and has been running for a considerable period of time.
In addition to the quality problems of the product itself mentioned above, the most common problems are caused by improper adjustment of equipment. For example, adjusting the back focus of a camera is a very detailed and precise task. If you do not adjust it carefully, problems such as poor focus or defocusing may occur during various operations of the three-variable lens. In addition, whether the positions of some switches and adjustment knobs on the camera are correct, whether they meet the technical requirements of the system, whether the decoder encoding switch or other adjustable parts are set correctly will directly affect the normal use of the equipment itself or the normal performance of the entire system.
D. Problems caused by incorrect connection between equipment (or components) and equipment (or components). Problems in this area will generally occur in the following aspects:
a. Impedance mismatch. If the video is connected to a monitor with high impedance, the image will be very bright and the characters will shake. Or characters may appear sometimes or not.
b. The communication interface or communication method is incorrect. This situation often occurs between the control host and devices that have communication control relationships such as decoders or control keyboards. This is mostly caused by the selected control host and decoder or control keyboard being products from different manufacturers. Generally speaking, the communication methods or transmission control codes used by different manufacturers are different. Therefore, products from the same manufacturer should be used for the host, decoder, control keyboard, etc.
c. Insufficient driving capability or exceeding the specified number of device connections. For example, the number of main control keyboards and sub-control keys corresponding to the control host is specified. Exceeding the specified number will cause the system to work abnormally. The working power of the decoder gimbal is lower than the actual gimbal, so it cannot drive the gimbal.
2. Analysis and solutions to transmission system failures
Video transmission is the most commonly used transmission system for TV surveillance. Due to space limitations, the following only analyzes the fault phenomena that occur under the video transmission method and proposes some solutions.
A. In video transmission, the most common fault phenomenon is 50-week power frequency interference. The manifestation is that a black or white bar appears on the monitor screen and slowly scrolls up or down. This phenomenon is mostly caused by a bad ground circuit in the system that introduces 50-cycle power frequency interference (alternating current interference). It should be mentioned that sometimes this fault phenomenon can occur due to poor power performance (or partial damage) of the camera or control host (matrix switcher) (sometimes two black or white bars may appear). Therefore, during analysis When this type of failure occurs, it is necessary to distinguish two different causes of the failure.
To distinguish whether it is a power supply problem or a ground loop problem, a simple method is to connect only one nearby camera output signal with a good power supply to the control host. If the above interference phenomenon does not appear on the computer, it means that there is no problem with the control host.
Next, a portable monitor can be connected to the video output of the front-end camera nearby, and each camera can be checked one by one to find out whether there are any cameras that are causing interference due to power problems. If so, process it. If not, the interference is caused by other reasons such as ground loops.
B. Wood grain-like interference appears on the monitor. The occurrence of this kind of interference will not drown out the normal image when it is slight, but when it is serious, the image will be unwatchable (or even destroy the synchronization). The causes of this failure phenomenon are many and complex. There are roughly the following reasons: the quality of the video transmission line is not good, especially the shielding performance is poor (the shielding network is not a high-quality copper wire network, or the shielding network is too thin and cannot provide shielding effect). At the same time, the line resistance of this type of video cable is too large, which causes large attenuation of the signal and aggravates the fault. In addition, the characteristic impedance of this type of video line is not 75Ω, and the distribution parameters exceed the regulations are also one of the reasons for the failure.
The cause of this kind of failure is difficult to determine, and because the construction has been completed (wiring has been completed) after the determination, it is difficult to solve it by changing the wiring. Therefore, the selection of video cables that meet standards and requirements must be guaranteed in advance. Never buy poor quality video cables just to save money, otherwise you will have endless troubles. Since the above-mentioned interference phenomenon is not necessarily a fault caused by a defective video cable, the judgment must be accurate and cautious. Only after other possibilities have been ruled out can the problem be considered from the perspective of a defective video cable. The way to judge is, after eliminating other possible causes of this failure, if possible, send the remaining video cables (if there are none left, you have to intercept a section of such cables in the system) to the inspection department for testing. . When the test results are unqualified, it can be determined that there is a cable quality problem. If there is really a cable quality problem, the best way is of course to replace all such cables with cables that meet the requirements. This is the best way to completely solve the problem. When the interference is not very serious, you can try to purify the power supply and supply power to the entire system through a UPS connected online, which can often reduce or basically eliminate the interference. However, this method sometimes does not have obvious effect due to different signal conditions in the space around the system, or sometimes it works and sometimes it does not work. Caused by the fact that the power supply of the power supply system is not "clean". The power supply referred to here is not "clean", which means that there are interference signals superimposed on the normal power supply (50-cycle sine wave). Most of this interference signal on the power supply comes from equipment using thyristors in the power grid. In particular, high-current and high-voltage thyristor equipment pollutes the power grid very seriously, which results in the power supply in the same power grid being unclean. For example, there are high-power silicon-controlled frequency and speed regulation devices, silicon-controlled rectifier devices, silicon-controlled AC-DC conversion devices, etc. in this power grid, which will cause pollution to the power supply. The solution to this situation is relatively simple. It can basically be solved by using purified power supply or online UPS power supply for the entire system.
C. There is a strong interference source near the system. This can be determined through investigation and understanding. If this is the reason, the solution is to strengthen the shielding of the camera and ground the video cable pipes. c. Failure caused by short circuit or open circuit between the core wire of the video cable and the shielding network. The manifestation of this kind of failure is to produce deep and chaotic large-area pattern interference on the monitor, so that the image is completely destroyed, and no image and synchronization signal can be formed. This situation often occurs on BNC connectors or other types of video connectors. As long as you carefully check these joints one by one, the problem can be solved.
Another thing about this kind of fault phenomenon is that it is easy to judge. That is, when this kind of fault occurs, it is often not a problem with all signals in the entire system, but only in those with bad connectors. On the way.
D. Failure phenomenon caused by mismatch of characteristic impedance of transmission lines. The manifestation of this phenomenon is the interference of several vertical bars with equal spacing on the monitor screen. The frequency of the interference signal is basically an integer multiple of the horizontal frequency. This is caused by the impedance mismatch caused by the characteristic impedance of the video transmission line being not 75Ω. If you use an oscilloscope to view the waveform of the interfered image, you will find that a higher amplitude horizontal frequency harmonic oscillation waveform is superimposed on the back shoulder of the horizontal synchronization head, and the interference is caused by this. Through waveform analysis and quantitative measurement of video cables, it will also be found that the distribution parameters of video cables whose impedance does not meet the requirements also do not meet the requirements. In fact, this is one of the causes of impedance mismatch. Therefore, it can also be said that this interference phenomenon is caused by the fact that the characteristic cathode impedance and distribution parameters of the video cable do not meet the requirements. This problem is usually solved by "connecting the resistor in series at the beginning" or "connecting the resistor in parallel at the terminal". It is worth noting here that when the video transmission distance is very short (generally within 150 meters), the above-mentioned interference phenomena may not necessarily occur when using video cables with the above-mentioned impedance mismatch and excessive distribution parameters. Therefore, in a system with greatly different transmission distances, do not be confused by the lack of interference in short distances when analyzing this fault phenomenon.
The fundamental way to solve the above problems is to ensure the quality when purchasing video cables. Cables should be sampled and tested if necessary.
E. Space radiation interference introduced by transmission lines.
This interference phenomenon is mostly caused by strong, high-frequency space radiation sources near the transmission system, system front-end or central control room. One solution to this situation is to understand the surrounding environment when setting up the system and try to avoid or stay away from the radiation source; the other solution is to strengthen the shielding of the front-end and central equipment when the radiation source cannot be avoided. The pipelines of transmission lines are made of steel pipes and are well grounded.
3. Other fault phenomena
A. PTZ failure. It is a common failure of a gimbal that it malfunctions shortly after use or cannot rotate at all. In addition to product quality factors, this situation is mainly caused by the following reasons:
Only the pan/tilt with the camera properly installed (that is, the camera sits on the upper part of the pan/tilt turntable) is allowed to be used. The hoisting method was adopted (that is, the camera was installed under the pan/tilt turntable). In this case, the hoisting method increases the operating load of the gimbal, so the transmission mechanism of the gimbal will be damaged or even the motor will be burned after a short period of use.
The total weight of the camera and its protective cover exceeds the load-bearing capacity of the gimbal. Especially for pan/tilts used outdoors, the weight of the protective cover is often too large, and there is often a problem that the pan/tilt cannot rotate (especially in the vertical direction). Outdoor pan/tilts may malfunction or even be damaged due to excessively high or low ambient temperatures, or poor waterproofing or antifreeze measures.
B. When the distance is too far, the keyboard cannot control the camera (including lens) and PTZ through the decoder. This is mainly caused by the fact that when the distance is too far, the control signal attenuation is too large and the control signal received by the decoder is too weak. At this time, a relay box should be installed at a certain distance to amplify the shaping control signal.
C. The image contrast of the monitor is too small and the image is light. If this phenomenon is not a problem with the control host and monitor itself, the transmission distance is too long or the attenuation of the video transmission line is too large. In this case, line amplification and compensation devices should be added.
D. The image definition 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 caused by the loss of the high-frequency end of the image signal being too large, so that signals with frequencies above 3MHz are basically lost. This situation may be due to the fact that 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 there is a concentrated equivalent capacitance between the core wire and the shielded wire of the transmission line in the transmission link. caused.
E. Hue distortion. This is a common fault phenomenon that occurs in long-distance video baseband transmission. The main reason is caused by the excessive phase shift in the high-frequency band of the signal caused by the transmission line. In this case, a phase compensator should be added.
F. The operation keyboard fails. When this phenomenon is checked and there is no problem with the connection, it can basically be determined to be caused by the "crash" of the operating keyboard. In the description of keyboard operation functions, there are generally methods to solve "crash", such as "machine reset", which can be solved by this method. If this cannot be resolved, the keyboard itself may be damaged.
G. The host does not switch images cleanly. The manifestation of this fault phenomenon is that the interference of other pictures is superimposed on the selected picture, or the interference of the horizontal synchronization signal of other images. This is caused by the poor quality of the host's matrix switching switch, which cannot meet the isolation requirements between images. If a radio frequency transmission system is used, it may also be caused by excessive cross-interference modulation and mutual modulation of the system.
A large-scale TV monitoring system that operates in conjunction with an anti-theft alarm is a system with high technical content and complex structure. Although various fault phenomena may occur, as long as the quality of the equipment and equipment selected is ensured and the construction is carried out in strict accordance with standards and specifications, there will generally be no major problems. Even if a problem occurs, as long as you analyze and think calmly, "prescribe the right medicine" and don't blindly dismantle it, the problem will be solved quickly.
H. Poor communication failure
The controlled gimbal or electric lens can sometimes move normally, sometimes it cannot (or delays), or it cannot stop after moving. Yes, the main reason is that there is a problem with the communication line. After confirming that the wiring and lines are correct, check the RS-485 communication terminal matching resistance (120Ω) on the decoder. Or disconnect the host interface and the farthest matching resistor, use a multimeter to measure the DC resistance RD of the single communication chip and the DC resistance R2 of the communication port of the entire system, and compare with the theoretical calculation (R2=R0/n, where n is the number of decoders connected in parallel in the entire system). If the difference is too large, it can be determined that there is a problem with the communication chip, and the problematic chip can be found through point-by-point elimination. If the communication line has many branches, each branch can be disconnected to determine the approximate scope of the communication failure.