YDIT detailed analysis of monitoring system common problems and solutions

Source:YDIT 誉德 Release time:2019/9/3 10:19:11 Views:1022

 

(Ultra-thin integrated lifter, paperless conference system) Problem 1: A black bar or white bar appears on the monitor screen, and slowly scroll up or down
When analyzing such failure phenomena, it is necessary to distinguish between two different causes of failure. To distinguish between a power supply problem or a ground loop problem, an easy way is to connect only one camera with a power supply without a problem on the control panel. If the above interference does not occur on the monitor. , then the control host has no problem. Next, a portable monitor can be used to connect to the video output of the front camera and check each camera one by one. If so, proceed with the processing. If not, the interference is caused by other reasons such as the ground loop.

Problem 2: Wood grain interference on the monitor
The appearance of such interference does not overwhelm the normal image when it is slight, and the image cannot be viewed (or even destroys the synchronization) when it is severe. The causes of such failures are more complicated and complicated. There are roughly the following reasons:
1. The quality of the video transmission line is not good, especially the shielding performance is poor (the shielding net is not a good quality copper wire mesh, or the shielding mesh is too thin to prevent shielding). At the same time, the line resistance of such video lines is too large, which causes a large attenuation of the signal, which is also a cause of aggravation. In addition, the characteristic impedance of such video lines is not 75Ω and the parameter is out of specification is also one of the causes of failure. Since the above-mentioned interference phenomenon is not necessarily a failure caused by a poor video line, the cause of such a failure is accurate and prudent in judging. Only when the other possibilities are excluded can we consider the bad point of the video line. If it is really a cable quality problem, the best way is to replace all of these cables and replace them with the required cables. This is the best way to solve the problem completely.
2. The power supply of the power supply system is not "clean". The power supply referred to here is not "clean", which means that an interference signal is superimposed on a normal power source (a 50-sine sine wave). The interference signals on such power sources are mostly from devices using thyristors in the power grid. Especially for high-current, high-voltage thyristor equipment, the pollution to the power grid is very serious, which leads to the power supply in the same power grid is not "clean". For example, there are high-power thyristor frequency modulation speed regulation devices, thyristor rectifier devices, thyristor AC/DC converters, etc. in the power grid, which will pollute the power supply. The solution to this situation is relatively simple, as long as the entire system is powered by a clean power supply or an online UPS.
3. There is a strong source of interference near the system. This can be judged by investigation and understanding. If this is the case, the solution is to strengthen the shielding of the camera and ground the pipeline of the video cable.

Question 3: The fault caused by short circuit and open circuit of the core wire of the video cable and the shielded cable
This type of fault is manifested by the generation of deeper and more chaotic large-area moire on the monitor, so that the image is completely destroyed, and the image and synchronization signals are not formed. This is often the case with BNC connectors or other types of video connectors. That is to say, when such a fault phenomenon occurs, it is often not a problem in the signals of the entire system, but only in the number of paths in which the joints are not good. As long as you carefully check these connectors one by one, you can solve them.

Problem 4: Failure phenomenon due to characteristic impedance mismatch of transmission line
This phenomenon is manifested in that a plurality of vertical strips of equal spacing are generated on the screen of the monitor, and the frequency of the interference signal is substantially an integer multiple of the horizontal frequency. This is due to the impedance mismatch caused by the characteristic impedance of the video transmission line being 75Ω. It can also be said that this interference phenomenon is caused by the fact that the characteristic impedance and distribution parameters of the video cable are not in compliance with the requirements. The solution is generally solved by the method of "starting series resistor" or "terminal paralleling resistor". In addition, it is worth noting that when the video transmission distance is short (usually within 150 meters), the above-mentioned interference phenomenon may not occur with the video cable having the above-mentioned impedance mismatch and excessive distribution parameters.


Question 5: Space radiation interference introduced by transmission lines
Most of this interference phenomenon occurs because there is a strong, high-frequency spatial radiation source near the transmission system, the front end of the system, or the central control room. One solution to this situation is to understand the surrounding environment when the system is established, try to avoid or keep away from the radiation source; another method is to strengthen the shielding of the front end and the center equipment when the radiation source cannot be avoided. The pipeline of the transmission line is made of steel pipe and well grounded. The fundamental solution to the above problem is to ensure quality when purchasing video cables. Sampling inspection of cables should be carried out when necessary (ultra-thin integrated lifter, paperless conference system).

Question 6: The failure of the gimbal
A gimbal does not work well or cannot rotate at all after use. It is a common malfunction of the gimbal. In addition to the factors of product quality, the emergence of this situation is generally caused by the following reasons:
1. Only the gimbal that is installed in the camera is allowed to be hoisted during use. In this case, the hoisting method leads to an increase in the operating load of the gimbal, so the use of the gimbal will soon cause damage to the transmission mechanism of the gimbal and even burn the motor.
2. The total weight of the camera and its protective cover exceeds the weight of the gimbal. Especially for the outdoor use of the gimbal, the weight of the protective cover is often too large, and the problem that the gimbal does not move (especially in the vertical direction) often occurs.
3. The outdoor cloud platform is faulty or even damaged due to excessive ambient temperature, low temperature, poor waterproofing and antifreeze measures.
4. When the distance is too far, the operation keyboard cannot remotely control the camera (including the lens) and the pan/tilt through the decoder. This is mainly because when the distance is too far, the control signal is attenuated too much, and the control signal received by the decoder is too weak. At this time, a relay box should be added at a certain distance to amplify the shaping control signal.

Question 7: The image contrast of the monitor is too small, and the image is light
This phenomenon is not a problem with the control host and the monitor itself, that is, the transmission distance is too far or the video transmission line is attenuated too much. In this case, the line amplification and compensation device should be added.

Problem 8: Image clarity is not high, details are lost, color signal loss or color saturation is too small when it is serious
This is due to the excessive loss of the high frequency end of the image signal, which is caused by the substantial loss of signals at frequencies above 3 MHz. In this case, the transmission distance is too far, and there is no amplification compensation device in the middle; or because the distributed capacitance of the video transmission cable is too large; or due to the concentrated distribution of the equivalent capacitance between the core wire and the shield wire of the transmission line in the transmission link Caused.

Question 9: Hue distortion
This is a phenomenon that is prone to occur in long-distance video baseband transmission. The main reason is caused by the high phase shift of the signal caused by the transmission line. In this case, a phase compensator (ultra-thin integrated lifter, paperless conference system) should be added.

Question 10: Operating the keyboard fails
This phenomenon can basically be determined by operating the keyboard "dead" when checking the connection without problems. The operating instructions of the keyboard generally have a method to solve the "dead", such as "machine reset", etc., can be solved by this method. If it can't be solved, it may be that the keyboard itself is damaged.

Question 11: Matrix switching to images is not clean
The phenomenon of such a fault phenomenon is that on the screen after the selection, the interference of other pictures is superimposed, or the interference of the line synchronization signals of other images is performed. This is caused by the poor quality of the main mechanism matrix switch and the requirement for isolation between images. If the RF transmission system is used, it may also be caused by excessive modulation and mutual modulation of the system (ultra-thin integrated lifter, paperless conference system).