The definition of common cable monitoring and common troubleshooting methods

The common cable monitoring is the video and audio signals and data stream signals captured by camera and monitor and other sensor devices. Through professional equipment, multiple terminal point signal loads are transmitted back to the front in a high-frequency cable for long distances. Real-time processing of the collected signals, and a transmission mode in which the front end and the rear end communicate with each other. The concept of common-cable monitoring was proposed in 2000 and was subsequently promoted by many companies in the following years. It is gradually accepted by the market.

The transmission technology transmits 20 points of audio, video, and control signals and two-way transmission of an inverted audio signal (customizable channels) in an ordinary cable (requiring SYWV75-7 or more cables). On the signal, we can transmit RS232 and RS485 industrial control signals, and can also match the protocols of other manufacturers, adopt transparent transmission methods, and can support the superposition processing of multiple partitioned cables so that we can solve the number of monitoring points. Can reach thousands of points, and the effect of the image can reach the national 4th or higher image standard, no difference with traditional video or optical fiber transmission video effects;

The common cable monitoring/one-touch system has many failures because of many monitoring points, many contacts, long lines, amplifiers, and splitters, and there are many tricks in failure. How to deal with it accurately and quickly? In addition to having a certain level of technology, we must also have a strong sense of dedication and responsibility. It is also a key to pay attention to the accumulation of experience and pay attention to certain methods.

First, the solution (1) A feature of the failure of a common cable monitoring system is that there is no image signal at a monitoring point or control failure does not affect other monitoring points, so that in the process of failure can basically be a headache. "This is completely adaptive to failures without a signal, but it is a different situation when the signal is not good."

(2) In the case of a staged test, if the signal to the control room is not good after a certain stage (for example, second stage) amplifier, the fault may be at this level, but it may be several stages later. For this reason, The test can be based on the size of the level of changes in the stage or jump back to check.

Second, technical skills and professionalism

It is easy to receive signals in the control room, but it takes a lot of pain to see good image signals in the control room. Sometimes responsibility is even more important than technology. It is impossible for engineering and technical personnel who engage in cable monitoring systems to fail to achieve professionalism. The following highlights some examples.

2.1 Electrical faults (1) The technicians found during debugging that the shielded wires of the steel strands and cables are live and the voltage is about 36V. At this time, the work of the common cable monitoring system is normal. 36V voltage is not high, it is easy to make people may be the illusion of induced voltage and do not care. However, after careful inspection, the higher the voltage, the power line was found to hit the steel strand at a distance of one kilometer, and the electric steel strand hit the strand of the cable monitoring system, causing the network to be charged. Fortunately, the network has been processed in segments and the voltage is not very high. When customers find the control room, they only feel the feeling of electric shock. Afterwards, everyone feels that they are afraid. Failure to deal with it in time will inevitably lead to a major accident.

(2) There is no image signal in a partition. After investigation, the amplifier was powered by 220V and was powered on site. When the amplifier cover was opened, the fuse was found to be broken. After the replacement, the amplifier was working normally. However, the street lamp next to it did not expect to light up at the same time, but its brightness was not enough. Pull out the plug of the amplifier's power cord and the street light is off. Why is this? It was originally an electrician who took care of the situation, only pulling a live line to supply street lights, and the zero line used the power supply neutral line of the amplifier. That is, the street lamp and the amplifier are connected in series. If they are both 15W, the voltage applied to them is 380/2=190V. After the wire is reprocessed, everything returns to normal.

(3) The customer reports that the image of a section is not clear. The amplifier here is to take 220V power locally, the input level of the amplifier is normal, and the output level of the amplifier is adjusted to the normal value. The fault can still be eliminated. Suspected amplifier is damaged, replaced, and the fault persists. The power supply voltage is only 140V. Is the power supply 220V of the wiring through the wind and rain, rust and poor contact, causing the supply voltage is insufficient. The voltage is too low to cause the amplifier to work abnormally, its manifestation phenomenon is varied too; There are horizontal horizontal stripes, there are vertical S-shaped stripes, some similar to rain, this should pay special attention to in handling the breakdown. Do not simply change equipment.

Failure of 2.2F head (1) Partition the recent image signal is not good, measure the output level of the sub-area is low, measure the output level of the amplifier is normal, measure the 408 inserter output level loss is much greater than 8dB, suspected possible The inserter is damaged. After the replacement, the fault remains. Carefully check the connection line between the amplifier and the inserter, and find that the F heads at both ends are not standardized. That is, the F head is inserted between the aluminum foil and the core, and the aluminum foil. The inner layer is not aluminum but plastic, ie, the inner layer is not conductive, and the F head is not connected to the shielded wire. When it was just installed, it was so-so as well, and for a long time, a malfunction appeared. Do a good job of F-head and troubleshoot. This kind of trouble should pay more attention to the power supply to the feeder, because it not only affects the passage of the signal, but also affects the passage of the alternating current.

(2) The image signal is not good, but it only closes the core of the route, but the signal is better when the shield is not connected. The technician measured the level of its branch output at about 70dB. Check that there is a connector on its line. When you take a look, the shielded wire and the core wire collide with each other. If you reconnect it, the fault will be eliminated. The characteristic of the touch line is that the level of the high-frequency end and the low-frequency end is significantly attenuated, while the attenuation at the low-frequency end is more. When measuring, only measuring the core level is higher than connecting the shield.

2.3 Poor Contact There are many contact points in the cable monitoring system. Each amplifier, splitter, distributor, and adapter is a connector. However, the quality of the connector often affects the transmission of the signal and has a greater impact on the low-frequency end. For this reason, pay special attention to the connector.

(1) Poor channel signal. Step by step from the monitoring point back to the investigation, in the first stage amplifier, the amplifier input signal level is normal, the output signal is also normal, but the input to the second stage amplifier is not normal, the level of the low-frequency end is smaller than the normal value Tens of dB, I suspect that the F-heads at both ends of the cable are not doing well, and the fault has not been eliminated. Is the cable problem? This possibility is very small. If it is a quality problem, its loss should also be larger at the high frequency end. Repeatedly measuring the amplifier output is no problem, carefully check the output hole and found that its reed has opened, the mouth is larger, causing the output port and the core wire is bad, replace a new amplifier and try everything.

(2) Ghosting occurs at several monitoring points of the low channel. Carefully sub-section monitoring, found that when the output of the previous amplifier is normal, the input to the next level begins to appear ghosting. This section of the cable had openings, initially believed to be caused by openings, but the degree of ghosting was also found to change when the temperature changed, and ghosts disappeared in colder weather. It can be seen that ghosting is caused by changes in the characteristic impedance of the cable. This section of cable has been used for many years and the replacement has returned to normal.

2.4 The signal is often interrupted or good or bad. (1) There is no signal at the monitoring point. It used to be good or bad. The area uses a 36V feeder power supply (video expander 701). After inspection, the power supply voltage does not come through, and inspections are performed step by step, resulting in faults in the adapter. Due to inadvertent installation, the reed's reeds are pushed aside, and only one side is in contact with the core. Such blowing or shaking of the wind can cause direct current to fail, and the signal sometimes does not pass. Reprocess it and return to normal.

(2) The image signal is good or bad. The work of the amplifiers was normal. They were measured with a field-strength meter. Finally, the target was concentrated on a piece of cable. The cable was removed and checked. The cable was found to be hit by an air gun. The air gun was between the core wire and the shield wire. Blowing is sometimes short-circuited and sometimes open-circuited, so that the customer's image signal is always good or bad.

(3) The image signal is interrupted frequently, and the time is approximately the same. After careful inspection, the waterproof of the amplifier is not good and the water enters, causing the three-terminal regulator to work abnormally. Replace the amplifier, improve the waterproof measures and eliminate the fault.

(4) The high channel signal is poor, and it's good or bad. After investigation, the amplifier was working properly, but it was at the input of the next-stage amplifier that the signal level was not normal, and the high-channel loss was serious. The line was inspected and the two-distributor water in the middle was found to be flooded. The waterproof cover was blown off by the wind. In this way, the signal loss with temperature changes is not the same, and the effect on the high frequency end is even greater. The distributor is replaced, the waterproof is reinforced, and the fault is eliminated.

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