Common interference solutions for cameras

Common interference solutions for surveillance cameras :

1. Wood-grained interference This type of interference occurs when the lightness does not overwhelm the normal image, and when it is severe, the image cannot be viewed (and even undermines synchronization). The cause of this kind of failure phenomenon is more and more 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 network is not a copper network with good quality, or the shielding network is too thin to be shielded). At the same time, the line resistance of such video lines is too large, which causes the signal to have a large attenuation is also aggravating the cause of the failure. In addition, the characteristic impedance of such a video line is not 75 Ω and one of the causes of the malfunction is that the parameter is out of specification. Since the above-mentioned interference phenomenon is not necessarily a fault caused by a defective video line, the reason for this failure should be accurate and careful when judging. Only from the point of view of the video line can be considered when other possibilities are excluded. If it is really a cable quality problem, the best way is of course to replace all of these cables and replace them with cables that meet the requirements. This is the best way to completely solve the problem.

(2) The power supply system is not "clean". The power source referred to here is not "clean" and means that an interference signal is superimposed on a normal power source (a 50-cycle sine wave). This type of interference signal on the power supply mostly comes from devices that use thyristors in the power grid. In particular, high-current, high-voltage thyristor devices have a very serious pollution to the power grid, which leads to the fact that the power supply in the same power grid is not "clean." For example, in this power grid, there are high-power thyristor frequency modulation speed control devices, thyristor rectifier devices, thyristor AC-DC converter devices, and so on, all of which will cause pollution to 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 through investigation and understanding. If this is the reason, the solution is to strengthen the shielding of the camera, as well as to ground the pipeline of the video cable.

2. Deep and chaotic large-area moire interferes when the image is completely destroyed, and the image and synchronization signal cannot be formed. This failure is caused by the short circuit and open circuit of the core wire of the video cable and the shield network. This happens mostly on BNC connectors or other types of video connectors. That is, when this kind of fault phenomenon occurs, it is not always the signal of the entire system that causes problems, but only appears in the number of poorly-connected paths. As long as you carefully check these joints one by one, you can solve.

3. The frequency of some interfering signals with equally spaced vertical bars is basically an integral multiple of the line frequency, which is due to impedance mismatch caused by the characteristic impedance of the video transmission line not 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 do not meet the requirements. The solution to this problem is usually solved by means of "connected resistors at the beginning" or "connected resistors at the terminals". In addition, it is worth noting that when the video transmission distance is short (usually within 150 meters), using the above video cable with impedance mismatch and excessive distribution parameters does not necessarily cause the above-mentioned interference phenomenon. The fundamental solution to the above problem is to ensure quality when purchasing video cables. When necessary, the cable should be sampled and tested.

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