Some minor problems and precautions of the monitor

1. A black bar or white bar appears on the screen of the monitor, and it scrolls up or down slowly. There may be two different causes of failure.

To distinguish between the problem of power supply and the problem of ground loop, a simple method is to connect only the output signal of a camera with no power problem to the control host. If the above interference phenomenon does not appear on the monitor , It means there is no problem with the control host. Next, you can use a portable monitor to connect to the video output of the front camera, and check each camera one by one.

If there is, it is dealt with. If not, the interference is caused by ground loops and other reasons.

2. The interference of wood grain appears on the monitor.

The appearance of such interference will not overwhelm the normal image when it is slight, and the image cannot be viewed when it is severe (even destroying the synchronization). The reasons for this failure phenomenon are many and complicated. 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 good quality copper wire network, or the shielding network is too thin to play a shielding role). At the same time, the line resistance of this type of video line is too large, so that the signal is greatly attenuated is also the cause of the increased failure. In addition, the characteristic impedance of this type of video cable is not 75 ohms, and the main parameter is beyond the specification is also one of the reasons for deliberately. Because the above-mentioned interference phenomenon is not necessarily a failure caused by a bad video, the cause of this failure must be accurate and cautious in judgment. Only after excluding other possibilities, can we consider from the perspective of poor video line. If it is really a cable quality problem, the best way is of course to replace all such cables and replace them with cables that meet the requirements. This is the best way to completely solve the problem.

There are strong sources of interference near the system. This can be judged by investigation and understanding. If this is the reason, the solution is to strengthen the shielding of the camera and ground the video cable.

3. A large area of ​​deep and chaotic interference occurs on the monitor, so that the image is completely destroyed, and the image and synchronization signal cannot be formed.

The failure caused by short circuit or open circuit of the core wire of the video cable and the shielding network. This kind of failure mostly occurs on BNC connectors or other types of video connectors. That is to say, when this kind of fault phenomenon occurs, it is not always that the signals of all channels of the entire system are faulty, but only appears on the channels with bad connectors. As long as the joints are carefully checked one by one, it can be solved.

4. There are several vertical bars with equal spacing on the screen of the monitor, and the integer multiple of the frequency of the interference signal.
Failure phenomenon caused by the mismatch of the characteristic impedance of the transmission line: This is caused by the impedance mismatch caused by the characteristic impedance of the video transmission line not being 75 ohms. It can also be said that this interference phenomenon is caused by the combination of the characteristic impedance and distribution parameters of the video cable that do not meet the requirements.
The method of solution is generally solved by the method of "start-end series resistance" or "terminal-parallel resistance". In addition, it is worth noting that when the video transmission distance is very short (generally within 150 meters), the use of the above-mentioned impedance mismatch and distribution parameters of the video cable is too large will not appear the above-mentioned interference phenomenon. The fundamental solution to the above problem is to ensure quality when purchasing video cables. If necessary, the cable shall be sampled and tested.

5. Several thin stripes interfere on the screen of the monitor.

Most of this interference phenomenon occurs because there are strong, high-frequency spatial radiation sources near the transmission system, system front end, or near the central control room.
One solution to this situation is to understand the surrounding environment when the system is established, and try to avoid or stay away from the radiation source:
Another method is to strengthen the shielding of the front end and central equipment when the radiation source cannot be avoided, and use steel pipes for the transmission lines and pipelines and good grounding.