Picture distortion and interference
In the video surveillance system, video signal transmission, whether using coaxial cable or digital network cable, in the transmission process, once the external interference signal intrusion, usually affect the picture quality, thereby reducing the monitoring effect. In the surveillance system, there are many reasons for video interference and noise, and it is difficult to fully and clearly summarize. However, it is certain that these interferences and noises come from both the equipment itself and the external environment. For different noise and interference, the method of exclusion is not the same. If it is the reason of the equipment itself, it usually can be solved simply by replacing the faulty equipment; however, it is more difficult to deal with interference signals caused by external lines and the environment. Next, we will analyze each of the twelve major phenomena mentioned above one by one in order to deepen the reasons for their occurrence.
The color of the video image is distorted and twisted: usually this problem is caused by a short circuit between the positive and negative electrodes after the analog coaxial cable is connected to the video, or after the coaxial core wire is bent, the micro-touch contact connector housing may be on the twisted pair transmission. The positive and negative poles of the converter of the transmitting end and the receiving end are connected inversely. In addition, it is also possible that the signal pins of the network line are connected incorrectly. This kind of problem will not damage the equipment, and only the positive and negative polarity can be changed;
The horizontal white or black ripple of the video screen moves toward the top of the screen: this is mostly caused by insufficient voltage, but in some cases, the AC voltage of the power supply is low, and the voltage drop exceeds the rated operating voltage of the camera or DVR by more than 10%. , Or DC power supply failure so that the voltage from 12V DC to 9V below will cause the screen to move. In addition, it may also be caused by a decrease of the current from the supply limit to a current condition in which the load device cannot be operated or a current harmonic generated by the power supply increase;
· Multiple black horizontal lines appear on the video screen: The phenomenon is caused by the signal lines being too thin, the cable pulling distance too long to cause the signal to be weak, or the signal distributor without amplification compensation is used;
There are two overlapping scenes on the video screen: this signal called “ghosting†has secondary reflections. This phenomenon is also known as overlap shadowing or afterglow. Most of the problems are caused by incorrect cable impedances or short circuit lengths. Delayed reflections; it is also possible that there are too many signal assignments, causing signal reflection delays;
Twill or right-to-left twill stripes appear on video: This type of twill or web-like interference appears on the video monitor. This kind of interference does not affect the normal image when it is light, but when it is serious, the video has problems with the general monitoring. This kind of phenomenon is numerous and complicated. First, the quality of the video transmission line may be poor, especially the poor performance of the shielding and isolation noise, poor quality of the isolation network, or the accumulation of noise due to a capacitive reactance caused by the aluminum foil plus the copper wire network; or the imbalance of the ground impedance is not 75Ω. Caused by floor wave noise entering the cable, if this part is serious, on the analog coaxial cable will produce an imbalance of the voltage to the ground, so that the cable becomes a capacitor case accumulation current, once the engineer touches the BNC connector will discharge, so that Engineers produce electric shock or discharge sparks to damage the equipment circuit; again, it may be due to the power supply system head and tail end not equal to the ground potential and the power source is not purely correct AC, but will also be caused by the wrong power phase. There is such interference; finally, there is a strong source of interference near the monitoring system, such as ground wave noise interference caused by high-frequency equipment or radio and television signal transmission towers in the vicinity;
Color and sound deviation
The color of the video screen becomes light and the colors are weird: In general, the problem is that there are many problems in adjusting the color saturation, but there are also problems caused by broken skin or poor grounding on the line.
The video screen jumps up and down continuously: If the next runout is not an excessively weak signal, the camera itself loses the level of the synchronization signal because of the adjustment of the grayscale signal; also, because the wire is not long enough during construction, the solder is not soldered during wiring. Welding, resulting in out of sync. In the case of multiple signals, the vertical sync signal caused by uneven intensity makes the screen jitter;
There are water ripples and bright spot noises on the video screen: This type of problem is mostly caused by poor aperture adjustment of the lens, but it is also possible that the field signal lines are disturbed by the external environment. Because the environment is often scattered with noise, resulting in the subtraction of the foreground and background, there are a lot of fragmented spots of non-moving objects, these spots will destroy the target information, and then cause the system to misjudgment, it is also one of the more difficult interference problems, but If simply refers to the bright spot noise, it may be the problem that the illumination can be solved by adjusting the aperture.
The video was originally in color format but turned black and white: even if it were a fool, the “stupid and naive†engineers would inevitably run into it. Since the current camera has the NTSC and PAL dual system selection function (whether analog or network surveillance cameras are all the same), some engineers found that after the camera was installed, the video could only display black and white images. It was just trying to check the lines. , monitors, and DVRs often ignore the camera's own system switching options. However, this is not an absolute and unique reason. It may also be the result of the group's resistance to changes caused by the short-circuiting of positive and negative poles of the line. Therefore, it must be carefully checked;
There are regular white highlights in the picture: this problem usually occurs when the video transmitter's line is poor or moisture in the connector penetrates into the fiber cable connector; of course, high-frequency devices can also cause the camera to produce such picture-interference noise, especially This phenomenon is most likely to occur in the near-range antenna of an FM AM radio station; in addition, poor monitoring of the grounding of the monitoring equipment may also occur.
In the dark areas of the video screen, bright colored patches of different colors, such as white, reddish or green, and blue, appear. The cause is similar to the previous problem, but this situation will only occur on digital optical transceivers, and its root causes Should be caused by improper processing of the signal demodulation circuit. The product quality of product manufacturers in this part will also affect the results of the project;
A second video interference situation occurs in video or sound: crosstalk is mainly caused by the mutual interference between the signal and the signal; it may also be caused by electromagnetic radiation between the signal wires, or transmitted from the power plane and the ground plane. The necessary signals are generated; it may also be due to the adjacent interference from the equipment or the excessive proximity between the cables and cables of different strengths and different types of signals.
After reading the above reasons, the reader may ask: It seems that such problems are not related to cables. This is true, because the quality of the cable construction is directly related to the quality of the project. Therefore, before discussing the problem of video noise interference, it is necessary to understand the influence of transmission of video frequency spectrum and coaxial cable on noise interference.
In the video surveillance system, video signal transmission, whether using coaxial cable or digital network cable, in the transmission process, once the external interference signal intrusion, usually affect the picture quality, thereby reducing the monitoring effect. In the surveillance system, there are many reasons for video interference and noise, and it is difficult to fully and clearly summarize. However, it is certain that these interferences and noises come from both the equipment itself and the external environment. For different noise and interference, the method of exclusion is not the same. If it is the reason of the equipment itself, it usually can be solved simply by replacing the faulty equipment; however, it is more difficult to deal with interference signals caused by external lines and the environment. Next, we will analyze each of the twelve major phenomena mentioned above one by one in order to deepen the reasons for their occurrence.
The color of the video image is distorted and twisted: usually this problem is caused by a short circuit between the positive and negative electrodes after the analog coaxial cable is connected to the video, or after the coaxial core wire is bent, the micro-touch contact connector housing may be on the twisted pair transmission. The positive and negative poles of the converter of the transmitting end and the receiving end are connected inversely. In addition, it is also possible that the signal pins of the network line are connected incorrectly. This kind of problem will not damage the equipment, and only the positive and negative polarity can be changed;
The horizontal white or black ripple of the video screen moves toward the top of the screen: this is mostly caused by insufficient voltage, but in some cases, the AC voltage of the power supply is low, and the voltage drop exceeds the rated operating voltage of the camera or DVR by more than 10%. , Or DC power supply failure so that the voltage from 12V DC to 9V below will cause the screen to move. In addition, it may also be caused by a decrease of the current from the supply limit to a current condition in which the load device cannot be operated or a current harmonic generated by the power supply increase;
· Multiple black horizontal lines appear on the video screen: The phenomenon is caused by the signal lines being too thin, the cable pulling distance too long to cause the signal to be weak, or the signal distributor without amplification compensation is used;
There are two overlapping scenes on the video screen: this signal called “ghosting†has secondary reflections. This phenomenon is also known as overlap shadowing or afterglow. Most of the problems are caused by incorrect cable impedances or short circuit lengths. Delayed reflections; it is also possible that there are too many signal assignments, causing signal reflection delays;
Twill or right-to-left twill stripes appear on video: This type of twill or web-like interference appears on the video monitor. This kind of interference does not affect the normal image when it is light, but when it is serious, the video has problems with the general monitoring. This kind of phenomenon is numerous and complicated. First, the quality of the video transmission line may be poor, especially the poor performance of the shielding and isolation noise, poor quality of the isolation network, or the accumulation of noise due to a capacitive reactance caused by the aluminum foil plus the copper wire network; or the imbalance of the ground impedance is not 75Ω. Caused by floor wave noise entering the cable, if this part is serious, on the analog coaxial cable will produce an imbalance of the voltage to the ground, so that the cable becomes a capacitor case accumulation current, once the engineer touches the BNC connector will discharge, so that Engineers produce electric shock or discharge sparks to damage the equipment circuit; again, it may be due to the power supply system head and tail end not equal to the ground potential and the power source is not purely correct AC, but will also be caused by the wrong power phase. There is such interference; finally, there is a strong source of interference near the monitoring system, such as ground wave noise interference caused by high-frequency equipment or radio and television signal transmission towers in the vicinity;
Color and sound deviation
The color of the video screen becomes light and the colors are weird: In general, the problem is that there are many problems in adjusting the color saturation, but there are also problems caused by broken skin or poor grounding on the line.
The video screen jumps up and down continuously: If the next runout is not an excessively weak signal, the camera itself loses the level of the synchronization signal because of the adjustment of the grayscale signal; also, because the wire is not long enough during construction, the solder is not soldered during wiring. Welding, resulting in out of sync. In the case of multiple signals, the vertical sync signal caused by uneven intensity makes the screen jitter;
There are water ripples and bright spot noises on the video screen: This type of problem is mostly caused by poor aperture adjustment of the lens, but it is also possible that the field signal lines are disturbed by the external environment. Because the environment is often scattered with noise, resulting in the subtraction of the foreground and background, there are a lot of fragmented spots of non-moving objects, these spots will destroy the target information, and then cause the system to misjudgment, it is also one of the more difficult interference problems, but If simply refers to the bright spot noise, it may be the problem that the illumination can be solved by adjusting the aperture.
The video was originally in color format but turned black and white: even if it were a fool, the “stupid and naive†engineers would inevitably run into it. Since the current camera has the NTSC and PAL dual system selection function (whether analog or network surveillance cameras are all the same), some engineers found that after the camera was installed, the video could only display black and white images. It was just trying to check the lines. , monitors, and DVRs often ignore the camera's own system switching options. However, this is not an absolute and unique reason. It may also be the result of the group's resistance to changes caused by the short-circuiting of positive and negative poles of the line. Therefore, it must be carefully checked;
There are regular white highlights in the picture: this problem usually occurs when the video transmitter's line is poor or moisture in the connector penetrates into the fiber cable connector; of course, high-frequency devices can also cause the camera to produce such picture-interference noise, especially This phenomenon is most likely to occur in the near-range antenna of an FM AM radio station; in addition, poor monitoring of the grounding of the monitoring equipment may also occur.
In the dark areas of the video screen, bright colored patches of different colors, such as white, reddish or green, and blue, appear. The cause is similar to the previous problem, but this situation will only occur on digital optical transceivers, and its root causes Should be caused by improper processing of the signal demodulation circuit. The product quality of product manufacturers in this part will also affect the results of the project;
A second video interference situation occurs in video or sound: crosstalk is mainly caused by the mutual interference between the signal and the signal; it may also be caused by electromagnetic radiation between the signal wires, or transmitted from the power plane and the ground plane. The necessary signals are generated; it may also be due to the adjacent interference from the equipment or the excessive proximity between the cables and cables of different strengths and different types of signals.
After reading the above reasons, the reader may ask: It seems that such problems are not related to cables. This is true, because the quality of the cable construction is directly related to the quality of the project. Therefore, before discussing the problem of video noise interference, it is necessary to understand the influence of transmission of video frequency spectrum and coaxial cable on noise interference.
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