What are the common faults in the monitoring system? How to solve it?

(one)

After a monitoring system enters into the commissioning phase, commissioning phase, and after delivery, there are likely to be such failure phenomena, such as: technical indicators that cannot function properly, the system cannot meet design requirements, and the overall performance and quality are not satisfactory. That is some 'soft problems'. These problems are inevitable for a monitoring project, especially for a complex, large-scale monitoring project.

1. Device failure caused by incorrect power supply.

Incorrect power supply may be as follows: The power supply line or power supply voltage is incorrect, the power is not enough (or the line diameter of a certain power supply line is not enough, the voltage drop is too large, etc.), the transmission line of the power supply system is short circuited, open circuited, instantaneously Pressure and so on. In particular, the device may be damaged due to power supply errors or instantaneous overvoltage. Therefore, in the commissioning of the system, before the power supply, it must be carefully checked and checked carefully and must not be taken lightly.

2. Because there are many links between certain devices (such as cameras with three variable lenses and the head), if the handling is not good, especially if the lines connected to the devices are not handled well, there will be open circuit, short circuit and line. Poor insulation, incorrect wiring, etc. result in equipment damage and performance degradation. In this case, the analysis should be made calmly based on the phenomenon of failure, and it should be determined on which of the lines that the connection is faulty. This will reduce the scope of the problem. It is particularly worth pointing out that cameras with pan-tilt heads have a long time due to all-round movements, resulting in disconnection and breakage of connections that are common. Therefore, special attention should be paid to the connection of equipment and various lines in this case to meet the requirement of long-term operation.

3. The quality of equipment or components itself.

In theory, quality problems may occur on various equipment and components. However, from an experience point of view, the pure quality of the product itself occurs in decoders, electric gimbals, and transmission components. It is worth noting that some equipment may not be unusable due to its overall quality, but it may not meet the specifications given in the product specification on certain technical indicators. Therefore, the necessary sample testing must be performed on the selected product. If it is indeed a product quality problem, the best way is to replace the product and not to dismantle and repair it.

In addition, the most common problems are due to improper adjustment of equipment. For example, the adjustment of the focal length after installation of the camera is very detailed and precise. If the adjustment is not carefully performed, problems such as poor focusing or defocusing during various operations of the three variable lenses may occur. In addition, whether the positions of some switches and adjustment knobs on the camera are correct, whether they meet the technical requirements of the system, the correctness of the encoder coding switch or other adjustable position settings directly affect the normal use of the device itself or affect the normal performance of the entire system. .

4. Problems arising from incorrect connection between equipment (or components) and equipment (or components) will generally occur in the following areas:

(1) Impedance mismatch.

(2) Communication interface or communication method does not correspond. This situation mostly occurs between the control host and a device such as a decoder or a control keyboard that has a communication control relationship. That is, the selected control host and decoder or control keyboard are not caused by a manufacturer's product. Therefore, the same manufacturer's products should be used for the host, the decoder, and the control keyboard.

(3) The drive capacity is insufficient or exceeds the specified number of device connections. For example, some picture splitters have an alarm input interface and a system host connected to an alarm probe, a long time delay recorder, etc. is provided in its product specification. If the alarm probe is connected to the screen splitter At the input, the probe's alarm signal will drive both the control panel and the screen divider. In this case, the problem of insufficient driving capacity often arises. The phenomenon shown is that although the screen divider can alarm, but the input alarm signal is weak and the work is not stable, resulting in the corresponding image of the camera that the alarm signal occurred on the monitor even though the camera is instantly converted to a full-screen image However, it is lost (cannot hold), and the image on the monitor is still the multi-image before the alarm.

One of the solutions to the above problem is to use a dedicated alarm interface box to connect the alarm probe signal with the screen splitter or video switching host. Secondly, when there is no alarm interface box, the signal expansion device can be designed and processed independently. Or drive the device.

The problems mentioned above may also sometimes occur in the output and distribution of video signals.

(b) 1. In video transmission, the most common symptom is the appearance of a black bar or white bar on the monitor screen, and it may scroll up or down slowly. Therefore, when analyzing such failure phenomena, two different causes of failures should be distinguished. To distinguish between power supply problems and ground loop problems, a simple method is to connect only one camera power output signal with no power problem to the control host. If the above interference does not occur on the monitor , then there is no problem with the control host. Next, a portable monitor can be connected nearby to the video output of the front camera and each camera can be checked one by one. If yes, handle it. If not, the interference is caused by ground loops and other causes.

2. There is a grainy disturbance on the monitor. The appearance of such interference does not drown out the normal image when it is light, and the image cannot be viewed (and even destroy synchronization) when it is severe. 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 referred to here is not 'clean', it means that the interference signal is superimposed on the normal power supply (50-sine 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.

3. The fault caused by the short circuit and open circuit of the core wire of the video cable and the shield network. This failure manifests itself in a deep and chaotic large-area moire on the monitor, so that the image is completely destroyed and the image and synchronization signals cannot be formed. This happens mostly on BNC connectors or other types of video connectors. That is, when this kind of failure phenomenon occurs, it is not always the signal of the entire system that leads to problems, but only appears in the number of unfavorable connections. As long as you carefully check these joints one by one, you can solve.

4. The failure phenomenon due to the mismatch of the characteristic impedance of the transmission line. The manifestation of this phenomenon is that a number of vertical bars with equal spacing are generated on the screen of the monitor, and the frequency of the interference signal is basically an integral multiple of the line frequency. This is due to impedance mismatch caused by the characteristic impedance of the video transmission line is not 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 the method of 'connected resistors at the beginning' and '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 will 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.

5. Spatial radiation interference introduced by the transmission line. This interference phenomenon is mostly caused by strong, high-frequency spatial radiation sources near the transmission system, the system front-end, or the central control room. One of the solutions to this situation is to understand the surrounding environment when establishing the system and try to avoid or stay away from the radiation source; another way is to strengthen the shielding of the front-end and center equipment when the radiation source cannot be avoided. The pipeline of the transmission line adopts steel pipe and is well grounded.

(three)

1. The failure of the PTZ.

A pan/tilt will not operate quickly or at all after it is used. It is a common fault of the PTZ. The appearance of this situation, apart from the factors of product quality, is generally caused by the following reasons:

(1) Only the pan/tilt head mounted on the camera is allowed to use the hoisting method. In this case, the hoisting method leads to an increase in the operating load of the pan/tilt. Therefore, the use of the hoisting method will soon lead to damage to the rotating mechanism of the pan/tilt, or even the burning of the motor.

(2) The total weight of the camera and its protective cover exceeds the weight of the PTZ. Especially for PTZs that are used outdoors, the weight of the protective cover is often too large, and there is often the problem that the PTZ will not move (especially the vertical direction).

(3) The outdoor pan/tilt head is faulty or even damaged due to bad ambient temperature, excessively low temperature, waterproof, and frost protection measures.

2. When the distance is too far, the camera (including the lens) and the pan/tilt cannot be controlled by the decoder through the operation keyboard.

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 installed at a certain distance to amplify the shaping control signal.

3. The image contrast of the monitor is too small and the image is light.

This phenomenon is not the problem of controlling the host computer and the monitor itself, that is, the transmission distance is too long or the attenuation of the video transmission line is too large. In this case, the line amplification and compensation device should be added.

4. The sharpness of the image is not high, the detail is lost, and when the color is severe, color signal loss or color saturation is too small.

This is due to the fact that the loss of the high-frequency end of the image signal is too large, resulting in the basic loss of signals above 3 MHz. In this case, either the transmission distance is too long and there is no amplification compensation device in the middle; or the distribution capacitance of the video transmission cable is too large; or the equivalent capacitance is concentrated in the transmission link between the core wire and the shielded wire. Caused.

5. Hue distortion.

This is a fault phenomenon that easily occurs in long-distance video baseband transmission. The main reason is caused by the large phase shift of the high frequency band caused by the transmission line. In this case, a phase compensator should be added.

6. The operating keyboard is malfunctioning.

This phenomenon can basically be determined as a result of operating the keyboard 'crash' when there is no problem in checking the connection. On the operating instructions of the keyboard, there are generally methods to solve the problem of 'crash', such as 'reset all', etc., which can be solved by this method. If it cannot be solved, it may be that the keyboard itself is damaged.

7. The host does not clean the image.

This failure phenomenon is manifested in the screen after the selection, the interference of other pictures superposed, or the interference of the line synchronization signals of other pictures. This is due to the poor quality of the host or matrix switch and the lack of isolation between images.