Video Optical Multiplexer has entered a mature stage, how to select the appropriate video Optical and how maintenance is still our concern in this article from the several aspects some discussion, hoping to help give the reader.
    Introduction

    Optical transmission equipment in the optical communication system, mainly for photoelectric conversion and signal transmission, with transmission capacity, distance, attenuation, immunity to electromagnetic interference ability and many other advantages, used in telecommunications, power, control, industrial control, video surveillance industry. Video Optical experienced a development process, from multimode to single mode from analog to digital technology has reached a mature stage.

    Digital non-compressed Optical introduced

    In the field of security, generally known as the Optical also refers to digital non-compression-type optical transceiver used to transmit video, data, Ethernet, audio and other information, the principle of multi-channel analog baseband video high-resolution digital audio, data, form a high-speed digital stream, multi-channel digital stream multiplexing through the launch of the Optical emission, receiver and then through the other side of the receiver Optical demultiplexing, restored the brightest digital signal by D / A converter analog video, audio, data restore. Digital Optical only A / D conversion of the quantization error, not enough to cause signal distortion, and allows video images, audio, data transmission quality is very satisfactory results. Its transmission is a digital signal, large-capacity transmission and does not interfere with each other, and multiple video, audio, data, Ethernet, telephone signal can be transmitted on the same fiber without crosstalk.

    Digital non-compressed Optical choice

    First, the user needs based on the actual needs of the project decided to use the transmission scheme - point-to-point type, node type. Video Optical point-to-point type for the most basic, is also used frequently in Optical work is one o'clock one point but can only be a point in front of another point, it is more a waste of fiber; node type using a series of hand in hand, set up multiple nodes on a fiber optic cable, you can save optical fiber to a larger extent.

    The principle of point-to-point PDH is the installation of a launch Optical front-end monitoring points will all kinds of electrical signals into optical signals, the optical signal through the terminal to receive Optical restore the signal transmitter and receiver machine with a fiber optic cable connection. Type optical transceiver of the node can also be called a bus Digital Optical division multiple points into the video signal in a core optical fiber (non-coding compression, no loss of video image) and the control signal to achieve the transmission of multiple signaling cascades.

    Such means of transmission which saves a lot of fiber resources used for highway and other applications with point by point insertion characteristics.

    Second, the user choice of Optical also need to implement the performance parameters to meet the requirements, according to the selection of types of optical devices and power Optical divided into a variety of transmission distance. If a company's Optical divided into Class A and 25 km, Grade B, 50 km, and C-level and 75 km. In addition to the distance away, users also need to carefully examine the technical parameters of the optical transceiver, such as SNR, differential gain, differential phase.

    Again, according to the appearance of simple discriminant Optical quality, such as high-grade Optical selection of the aluminum alloy shell and profile rail, with the heat, rust-proof and easy installation features. Better Optical video and data interfaces with surge protection, users can directly observe the Optical specialized ground electrode to determine.

    Finally, when the user select the Optical brand, but also give full consideration to the manufacturer's service system, whether the companies with service centers in the region, so that the failure timely maintenance of the manufacturers. In addition, the product is the relevant test report and manufacturers about the qualification and are also factors to be considered in product selection.

The use and maintenance of Optical

    Optical power supply and installation environment

    The general transmitter installation location to follow the front-end video capture device, so installation location are more dispersed, with independent chassis to the power supply. In the security monitoring of power supply is usually in two ways: centralization of power and the local electricity supply, Optical transmission site, the front-end distance farther, it is less centralized power supply. The receiver generally located in the engine room of the monitoring center, unlike the transmitter then dispersed on the power supply chassis with the front of the transmitter uses the same power supply, a lot of space occupied by engine room, it is disorganized, can not be unified management . Center of the receiver power supply plug-in chassis, power supply, not the slot studded every few slots open space, Optical cooling. Should be noted that the impact of the laser component of the Optical and photoelectric conversion module is very sensitive to transient pulse current, and therefore should not be frequent switching machine.

    Multi-front-end transmitter is installed in the front-end distribution box to do the dustproof and waterproof distribution box, distribution box plug and more full conducive Optical cooling is necessary to consider the distribution box with fan. The monitoring center computer room to keep the environment clean and tidy, always pay attention to clean up, do not knot dust, preferably packed into a room decoration after a good room, in case the engine room renovation, should be promptly cleaned up. General there will be a lot of equipment in the engine room centrally installed in the cabinet, equipment heat, ventilation and in poor condition, it is best to install air-conditioning system to guarantee Optical.

    To do the installation Optical-site protective measures, moisture-proof, waterproof, dustproof, bearing in mind the actual operation of the site must be equipped with the appropriate use of optical fiber, fiber can not use incomplete failure, if you do not match, would severely affect the light end machine transmission quality when it comes to fiber optic cable welding and pay attention to the measurement of fiber optic light attenuation or loss in the range of valid values.

    Optical lightning

    Optical transmitter as a front-end equipment is usually installed in the outdoor equipment boxes, the environment of the scene is quite bad, mine was extremely important, lightning protection measures will directly determine the probability of the optical transceiver failure. Lightning failure modes are divided into direct lightning stroke lightning and back ground in three forms, the most serious impact on the Optical, mainly to counter potential.

    The so-called back ground when lightning and other air-termination system will direct lightning stroke powerful lightning current into the earth after the deflectors and the grounding vent deflectors, grounding, and connected with metal objects will produce a very high instantaneous voltage, high voltage would be close to them, but there is no direct contact with metal objects, cable and other electronic equipment have a huge potential difference, this potential difference caused by electric shock is the back ground. To counter potential damage Optical following forms: when lightning stemming the flow into the earth, the ground potential of the grounding grid in a few microseconds to raise tens of thousands or hundreds of thousands of volts. Highly destructive lightning current ground portion of the flow of these devices from a variety of devices, or through the breakdown of the earth insulation and the flow of other nearby devices, and ultimately cause the destruction or damage of equipment (destruction is shown in Figure 2), damage to some of the major : Chassis power supply PCB, electronic components, video interface chip and its associated electronic components, audio and data ports at the chip.

    Although a variety of forms of lightning damage, but can still adopt a scientific protective measures to reduce Optical fault occurrence probability. First, to ensure good grounding device is the premise of lightning protection measures, because all the induced current is the last to escape into the earth. In general, the smaller the discharge effect of grounding resistance as possible, usually to control the grounding resistance is better in less than 4 ohms, you can use ground clamp to measure the grounding resistance. For some high soil resistivity, we can consider the reduction agent in the soil, thereby reducing the grounding resistance. Secondly, the front-end equipment to the installation of surge protectors, the normal voltage, the surge protector was a high impedance state, only a small leakage current, power loss is very small, when the line appears in overvoltage, surge protection was low resistance state, over-voltage surge protector in the form of the discharge current into the earth, over-voltage suppression down to the line voltage is restored to normal after the surge voltage, surge protection device showed a high impedance insulation, therefore surge The protection must be co-ordinated with a good grounding device. Front of the camera video signal output port and transmitter video input at the entrance to access the surge protector if the transmitter is connected to other data lines, you need to control the beginning and end of the signal line side installation of a data mine, plus power mine and mine equipment such as cameras and Optical power input. Make sure that mine close to the access port installed SPD, SPD distance video port data port is too far to play not lightning effect.

    Plus a good lightning protection equipment, and the rest is ground network design problems. Ground pile is absolutely necessary in place to ensure the Optical good grounding and a good low impedance ground network design to ensure the lightning protection system equipment to play with good results and can effectively balance the various parts of the voltage in the entire transmission system to prevent potential difference the interference of the line equipment, but also can effectively avoid counter potential damage to the equipment.

Optical debugging

    After you do the above points, will begin normal debugging, mainly fiber optic and data path debugging. Many types of optional Optical data, according to the actual needs of the scene, field use Optical data of different types in the debugging must refer to the appropriate instructions, in accordance with the instructions on the data dial and interface definitions for data wiring.

    Optical on-site installation environment is complex, some users in the debugging does not make sense usually first suspected fault, in fact, the optical transceiver product technology is very mature products before they leave the factory after repeated tests and pagers, so the product itself, the problem less likely, therefore, need to consider in the first scene is the installation problem, can go to troubleshoot from the following aspects:

    Optical fiber itself has not been tested, translucent or instability of the optical path or optical attenuation is too large;

    Front-end equipment failure, such as the camera has no video or no power;

    And back-end equipment failure, such as a monitor video, keyboard control protocol is not beyond their control;

    Connect line failure, such as video head no welding good barrier, and control lines are wrong, or the cable cross-pick the wrong, and reversed.

    The above phenomenon, especially the probability of occurrence of line fault when problems need to be carefully examined. Troubleshooting, you can use the exclusion method, a device is a device to exclude, and finally to accurately determine the key. Recommended that the user to determine whether the Optical transmitter and receiver together close test should not pass, compared with PDH itself fault, you need to swap contact with manufacturers. In order to reduce the problem, the user as much as possible before installation, close the test Optical thus quickly through the installation and commissioning, saving the construction period.

    Optical daily maintenance

    Usually the situation Optical working environment is quite poor, when used to keep the cleaning of the fiber head. Optical is very sensitive to dust, and PDH during transport or use for some time, there may be the mouth of the fiber dust or debris caused by congestion, which affects the normal transmission of video and data at this time industrial absolute alcohol and dust-free paper can be used for cleaning the fiber head, to avoid adhesion of dust.

    Optical fiber jumper within and external fiber connection adapter, the adapter is usually for the ceramic core, plug the fiber head to pay special attention to, Do not force to prevent improper squeeze crack the ceramic casing or crushed, resulting in not function properly Optical transmission signal.

    Conclusion

    Video Optical technology is mature, stable, low cost, the first choice of long-distance transmission projects in the current video, some of Optical manufacturers through technical innovation, the introduction of more powerful fiber-optic transmission systems. With the video monitoring system to networking, high definition, optical transceiver manufacturers responding with new products, analog video, network video transmission, management and image storage capabilities together to improve fiber utilization.