When video transmission, there are often some malfunction, such as without
images, video stream not smoothly, monitor screen interference, etc. In the
article, there will list five common monitor screen interference and also tell
you how to deal with them.
The most common fault phenomenon displays on the monitor screen: black or white horizontal line scrolling up or down slowly. Then, when analysis of such symptoms, it needs distinguish two different causes of failure. There are two factors: power supply or earth loop problems. The easy way to distinguish problem is that in the control panel, getting the nearest camera output signal with good power supply. If there is no interference with the horizontal line, the control panel is OK. Next, get an available potable monitor connected to one camera’s video output terminal, and check each camera individually. If there is interference, then processes. If no, the interference is caused by earth loops or other reasons.
When monitor displays slight grainy interference, the normal image will not be drowned. While serious, the image can not be watched (even destroy synchronization). The reasons for this failure phenomenon are more complex. Generally, there are some reasons:
A, The quality of video transmission is not good, especially poor shielding properties (shield wire is not good quality copper wire, or shield wire is too shin to shield.) Also, line resistance of this video wire is larger; the greater attenuation of signal is also one of the reasons for aggravated fault. In addition, the Characteristic Impedance of this video cable not 75Ω or beyond the prescribed parameters of 75Ω is also one of the reasons for failure. As the failure caused by bad video cable is uncertain of the reason for the grainy interference phenomenon, we should be careful to decide the cause of phenomenon. Only after we exclude other possible, we can consider problem from bad video cable. If it is the cable quality problem, the best way to solve of course is to replace all the cable with required cable.
B, Grainy interference is caused by “not clean” power supply. The named “not clean” power supply means that there is superimposed interfering signal (50Hz sine wave) on the normal power supply. Such interfering signal of power supply often comes from devices used SCR in current grid, especially SCR devices with high current and high voltage. For example, if there are high-power SCR FM speeders, SCR rectifying devices and SCR RF conversion devices, etc. all of these devices will generate pollution. The solution is relatively simple, just opting purification power supply or online UPS supplying power for the entire system.
C, There is strong interference source near the system. This can be judged by investigation. If this is the reason, to solve problem by strengthening he shield of camera and ground connection the pipeline of video cable.
The wavy interference causes by failure of short circuit between the core wire of video cable and shielded wire. When there are deeper and messier large wavy interference, the image will be completely destroyed and won’t form an image and synchronization signals. This always happens at the BNC connectors or other types of video connectors. Therefore, every signal of the whole system won’t get problem, but those channels with bad connectors. Just check these joints one by one, problem can be resolved.
Five, other interference
There is space radiation interference introduced by the transmission wire. Such interference phenomenon mostly caused by the stronger, higher frequency space radiation source near the transmission system, system front-end or central control room. One of the solutions for such case is to learn the surrounding environment of the system created, and to try to avoid or be away from the radiation source. The other way is to strengthen shielding of the front-end and central equipment, or opt for steel pipes and ground connection for the pipeline of transmission wire, if there is no way to avoid radiation source.
The above are some common interference happened on the screen of video monitor. Do you know all the phenomenon and how to solve the related cases? Well, it is not hard! Welcome your kindly comments!
First, interference with horizontal line
The most common fault phenomenon displays on the monitor screen: black or white horizontal line scrolling up or down slowly. Then, when analysis of such symptoms, it needs distinguish two different causes of failure. There are two factors: power supply or earth loop problems. The easy way to distinguish problem is that in the control panel, getting the nearest camera output signal with good power supply. If there is no interference with the horizontal line, the control panel is OK. Next, get an available potable monitor connected to one camera’s video output terminal, and check each camera individually. If there is interference, then processes. If no, the interference is caused by earth loops or other reasons.
Second, grainy interference
When monitor displays slight grainy interference, the normal image will not be drowned. While serious, the image can not be watched (even destroy synchronization). The reasons for this failure phenomenon are more complex. Generally, there are some reasons:
A, The quality of video transmission is not good, especially poor shielding properties (shield wire is not good quality copper wire, or shield wire is too shin to shield.) Also, line resistance of this video wire is larger; the greater attenuation of signal is also one of the reasons for aggravated fault. In addition, the Characteristic Impedance of this video cable not 75Ω or beyond the prescribed parameters of 75Ω is also one of the reasons for failure. As the failure caused by bad video cable is uncertain of the reason for the grainy interference phenomenon, we should be careful to decide the cause of phenomenon. Only after we exclude other possible, we can consider problem from bad video cable. If it is the cable quality problem, the best way to solve of course is to replace all the cable with required cable.
B, Grainy interference is caused by “not clean” power supply. The named “not clean” power supply means that there is superimposed interfering signal (50Hz sine wave) on the normal power supply. Such interfering signal of power supply often comes from devices used SCR in current grid, especially SCR devices with high current and high voltage. For example, if there are high-power SCR FM speeders, SCR rectifying devices and SCR RF conversion devices, etc. all of these devices will generate pollution. The solution is relatively simple, just opting purification power supply or online UPS supplying power for the entire system.
C, There is strong interference source near the system. This can be judged by investigation. If this is the reason, to solve problem by strengthening he shield of camera and ground connection the pipeline of video cable.
Third, wavy interference
The wavy interference causes by failure of short circuit between the core wire of video cable and shielded wire. When there are deeper and messier large wavy interference, the image will be completely destroyed and won’t form an image and synchronization signals. This always happens at the BNC connectors or other types of video connectors. Therefore, every signal of the whole system won’t get problem, but those channels with bad connectors. Just check these joints one by one, problem can be resolved.
Fourth, vertical stripe interference
The fault phenomenon of vertical
stripe interference causes from mismatch characteristic impedance of the
transmission wire. There are several pieces of equally spaced vertical stripe
interference on the monitor screen. The frequency of the interference signal is
basically an integer of the line frequency, which is due to the characteristic
impedance of video transmission cable not 75Ω and caused impedance mismatched.
The solutions often rely on “the top series resistance” or “the terminal
parallel resistance”. In addition, it is worth noting that, when the video
transmission distance is very short (less than 150m), there will not be the
above interference if opting video cable with impedance mismatched and larger
distribution parameters. Then, the fundamental solution is to ensure the quality
of purchased video cable and to do sampling inspection for the cable.Five, other interference
There is space radiation interference introduced by the transmission wire. Such interference phenomenon mostly caused by the stronger, higher frequency space radiation source near the transmission system, system front-end or central control room. One of the solutions for such case is to learn the surrounding environment of the system created, and to try to avoid or be away from the radiation source. The other way is to strengthen shielding of the front-end and central equipment, or opt for steel pipes and ground connection for the pipeline of transmission wire, if there is no way to avoid radiation source.
The above are some common interference happened on the screen of video monitor. Do you know all the phenomenon and how to solve the related cases? Well, it is not hard! Welcome your kindly comments!
No comments:
Post a Comment