16bits 20bits 24bits, the higher the bit rate, the more detailed it can reflect the subtle changes of sound.
2. Sampling accuracy:
48K 96K(CD sampling accuracy is 44. 1KHz/s), and professional audio optical terminals generally adopt 48K sampling, and 96K is a future direction.
3, signal-to-noise ratio
That is what we usually call dynamic range, and the unit is DB. The relationship between the dynamic range and the bit rate is that the dynamic range increases by 6dB with the increase of the bit rate of 1. At 16 bit, the dynamic range is 96dB. This can meet the general requirements, and the dynamic range of 24 bits can reach 144 dB, which is fever-level. Therefore, the current professional optical transceiver indicators can be summarized as: 24-bit 48K sampling 90DB.
Audio optical transceiver is divided into 1 ~ n channels of audio or 1 channels of control data. Attention should also be paid to the details of mono/bi-channel (and stereo), unidirectional/bidirectional, balanced output/unbalanced output in audio. Digital uncompressed transmission
● 8-bit digital coding is adopted for video.
● Color image signal
● High quality real-time transmission
● 10 Hz -24 kHz sound bandwidth
● Fully compatible with NTSC, PAL and SECAM images.
● It can transmit RS232, RS485 and RS422 standard data.
● Ethernet signals can be transmitted at the same time.
● The indicator lamp helps to diagnose system faults quickly.
● High reliability under various outdoor conditions.
● Support network management function.
● Simple installation, no need to adjust 1. Optical jumper.
It mainly plays the role of connection, connecting the optical transceiver with the optical fiber. Then from the connectors at both ends of the optical jumper, the optical jumper can be divided into FC jumper, ST jumper and SC jumper. According to the length of optical jumper, it can be divided into 3m jumper, 5m jumper and 10m jumper.
Common optical fiber specifications: single mode: 8/ 125μm, 9/ 125μm,1125μ m, multimode: 50/ 125μm, European standard 62.5//kloc-.
2. Junction box
The junction box, also known as the fusion box, mainly protects the fusion joint between the optical fiber jumper and the optical fiber, and fuses the optical fiber and the jumper into the junction box through the optical fiber fusion machine. Usually, each optical transmitter in the front end needs one junction box, and the central control room only needs one junction box. In terms of volume, the junction box can be divided into 8 ports, 12 ports and 24 ports.
3. Flange
Flange is also a kind of connector. Usually, there is an optical fiber interface on the optical transceiver, which is the flange, that is, the connector connecting the optical jumper and the optical transceiver. According to its specifications, it can be divided into FC, ST and SC.
4, light welding machine
It mainly fuses optical fiber and optical jumper together through electrodes under the condition of instantaneous discharge. When welding, pay attention to the neat cutting of the fiber end face and keep the end face clean.
5.OTDR optical time domain reflectometer
This is a kind of testing instrument, which mainly detects whether there is fiber breakage during fiber transmission.
6. Optical power meter
Literally, it is an instrument for measuring power, but it does not measure voltage power, but the power of light in optical fiber transmission and the attenuation of light in the transmission process.
In engineering application, the audio-video optical transceiver we use is different from the application of telephone optical transceiver:
1) Audio/video optical transceiver is usually used in security systems with audio signals and video signals to transmit the video of surveillance cameras and the audio of surveillance heads; Telephone optical transceiver is called PCM, which belongs to traditional telecom products, such as transmitting 30 program-controlled telephones through optical fiber.
2) If the traditional 2M network wants to transmit video, it needs to be equipped with an audio and video codec, so that audio and video can be transmitted through SDH network.
3) In the market, audio and video transceivers differentiate product quotations according to the number of routes, including 1, 2, 4, 8, 16, and telephone transceivers are superimposed on the same motherboard. For example, the price difference between the 6-way telephone and the 7-way telephone on the 8-way motherboard is not big, and the price difference between the 25-way telephone and the 30-way telephone on the 30-way motherboard is not big.
4) Audio/video optical transceiver and telephone optical transceiver can be superimposed with Ethernet and industrial control data. , depending on the practices of various manufacturers.
5) A core fiber can transmit 128 uncompressed videos at most, and a core fiber can transmit 480 telephones at most (30/e1* 6e1= 480)1,optical transceiver power supply and installation environment.
In general, the installation position of the transmitter follows the front-end video acquisition equipment, so the installation position is scattered, and an independent shell is needed to supply power for it. There are usually two power supply modes for security monitoring: central centralized power supply and local power supply. Because of the long distance between the front and rear ends of the scene transmitted by the optical transceiver, centralized power supply is rarely used. Receivers are generally located in the computer room of the monitoring center, not as scattered as transmitters. If the power supply mode is the same as the front-end transmitter, it will occupy a lot of space in the computer room, which is chaotic and cannot be managed in a unified way. Therefore, the power supply of the central receiver can be provided by the plug-in chassis, instead of filling all slots, one slot can be opened every few slots, which is beneficial to the heat dissipation of the optical transceiver. It should be noted that the laser module and photoelectric conversion module of optical transceiver are most afraid of the impact of instantaneous pulse current and should not be switched frequently. Most front-end transmitters are installed in the front-end distribution box, so they should be dustproof and waterproof. When the distribution box is full, in order to facilitate the heat dissipation of the optical transceiver, the distribution box with fan should be considered. The computer room of the monitoring center should keep the environment clean and tidy, and always pay attention to cleanliness and no dust. It is best to put the equipment into the computer room after it is renovated. In case of renovation of the computer room, it should be cleaned in time. Generally, a lot of equipment in the computer room will be installed in the cabinet, and the equipment will generate a lot of heat. When the ventilation and heat dissipation conditions are poor, it is best to install an air conditioning system to ensure the normal work of the optical transceiver. When installing the optical transceiver, the site protection measures such as moistureproof, waterproof and dustproof should be taken. At the same time, we should pay attention to the actual operation on site. Suitable optical fibers must be equipped, and defective optical fibers cannot be used. If they do not match, the transmission quality of optical transceiver will be seriously affected. When it comes to optical cable welding, it is also necessary to measure the optical attenuation or loss of optical cable within the effective value range.
2. Lightning protection of optical transceiver
Optical transceiver, especially the transmitter as front-end equipment, is usually installed in outdoor equipment box, and the site environment is quite bad, so lightning protection is extremely important. The quality of lightning protection measures directly determines the failure probability of optical transceiver. The damage modes of lightning are mainly divided into three forms: direct lightning, induced lightning and ground potential counterattack, and the ground potential counterattack is the most serious one that affects the optical transceiver.
The so-called ground potential counterattack refers to that when lightning receptors such as lightning rods leak the powerful lightning current of direct lightning into the earth through the down conductor and grounding body, they will generate quite high instantaneous voltage on the down conductor, grounding body and metal objects connected with them. This high voltage will generate huge potential difference between metal objects, cables and other electronic devices that are close but not in direct contact. The electric shock caused by this potential difference is the ground potential counterattack. There are several ways to destroy the optical transceiver by ground potential counterattack: when lightning current leaks into the earth, the ground potential of the grounding grid will rise to tens of thousands or hundreds of thousands of volts in a few microseconds. The extremely destructive lightning current will flow from the grounding part of various devices to these devices, or flow to other nearby devices through the breakdown of ground insulation, which will eventually cause the damage or destruction of the devices (see Figure 2 for the schematic diagram of the damage). The damaged parts mainly include: electronic components on the chassis power PCB, chips at the video interface and related electronic components, and chips at the audio and data ports.
Although there are various forms of lightning damage, scientific protective measures can be taken to reduce the probability of optical transceiver failure. First of all, ensuring the good effect of grounding device is the premise of lightning protection measures, because all induced currents will eventually leak into the earth. Generally speaking, the smaller the grounding resistance, the better the leakage effect. Generally, it is better to control the grounding resistance within 4 ohms, and the grounding resistance can be measured with a grounding clamp meter. For some places with high soil resistivity, we can consider adding resistance reducer to the soil to reduce the grounding resistance. Secondly, the front-end equipment should be equipped with surge protectors. When the voltage is normal, the surge protector is in a high resistance state, with only a small leakage current and a small power loss. When there is overvoltage on the line, the surge protector is in a low resistance state, and the overvoltage flows into the earth through the surge protector in the form of discharge current and is suppressed. After the surge voltage, when the line voltage returns to normal, the surge protector is in a high-resistance insulation state, so the surge protector must have a good grounding device to cooperate with it. The surge protector is connected to the video signal output port of the front camera and the video input port of the transmitter. If the transmitter is connected with other data lines, it is necessary to install data lightning protection devices at the beginning and end of the control signal line, and add lightning protection devices such as power lightning protection devices to the power input ports of cameras and optical terminals. When installing the lightning arrester, the lightning arrester must be close to the manhole. If the lightning arrester is too far away from the video port and data port, the lightning protection effect will not be exerted.
After installing lightning protection equipment, the remaining problem is the design of grounding grid. Grounding piles must be put in place to ensure good grounding of optical transceiver. A good design of low impedance grounding grid can ensure the lightning protection equipment in the system to play a good role, effectively balance the voltage of all parts of the whole transmission system, prevent the interference of ground potential difference to the equipment in the line, and also effectively avoid the damage of ground potential counterattack to the equipment.
3. Debugging of optical transceiver
After that, we started the normal debugging, mainly the debugging of optical fiber and data channel. Because there are many optional types of optical transceiver data, the types of optical transceiver data used in the field are different according to the actual needs of the field. When debugging, you must refer to the corresponding instructions and define the connection data according to the data dialing and interface in the instructions.
Due to the complex field installation environment of optical transceiver, when debugging fails, some users usually suspect that the product is faulty at first. In fact, the technology of optical transceiver products is very mature, and the products have been repeatedly tested and copied before leaving the factory, so the possibility of problems in the products themselves is relatively small. Therefore, when there is a problem on site, the first thing to consider is the installation problem, which can be investigated from the following aspects:
The optical fiber itself has not been tested, the optical path is blocked or unstable or the optical attenuation is too large;
Front-end equipment failure, such as no video or no power in the camera;
Back-end equipment failure, such as no video on the display, incorrect keyboard control protocol, uncontrollable by itself, etc.
Connecting cable failure, such as improper welding of video head, wrong connection of control line, or cross or reverse connection of connecting cable.
The above phenomenon, especially the line fault, has the highest probability, so you need to check it carefully when you encounter problems. When troubleshooting, you can use the troubleshooting method, one device at a time, and finally accurately judge the key points of the problem. When judging whether there is a problem with the optical transceiver, users are advised to put the transmitter and receiver together for close-range test. If it still doesn't work, it's the problem of the optical transceiver itself, and you need to contact the manufacturer to replace it. In order to reduce problems, users should test the optical transceiver as close as possible before installation, so as to quickly pass the installation and debugging and save the construction period.
4. Daily maintenance of optical transceiver
Usually, the working environment of optical transceiver is quite bad, so attention should be paid to keeping the optical fiber head clean when using it. Optical transceiver is very sensitive to dust, and dust or sundries may appear at the optical fiber port during transportation or after customers use it for a period of time, which will affect the normal transmission of video and data. At this time, the optical fiber head can be cleaned with industrial anhydrous alcohol and dust-free paper to avoid dust adhesion.
The optical fiber jumper inside the optical transceiver is connected with the external optical fiber through the adapter. Usually, the adapter is a ceramic die, so special attention should be paid when plugging and unplugging the optical fiber head. Don't use too much force, so as not to break or crush the ceramic sleeve, and the optical transceiver can't transmit signals normally. Optical transceiver is a transmission device in optical communication system, which mainly completes photoelectric conversion and transmission functions. Optical transceivers are usually used in pairs and consist of transmitters and receivers. The transmitter processes the user's analog signals through amplification, A/D conversion and multiplexing. Finally, the electrical signal is converted into an optical signal that can be transmitted through optical fiber through electrical/optical conversion, and transmitted to the receiver through optical fiber. At the receiving end, the opposite process is performed. Firstly, the received optical signal is converted into an electrical signal through optical/electrical conversion, and the electrical signal is demultiplexed, and then sent to the client through D/A and amplification filtering. The principle of different kinds of optical terminals is the same. Optical transceiver usually refers to the optical transceiver used in monitoring system to transmit video, data, Ethernet, audio and other comprehensive information. It is mainly divided into analog optical transceiver and digital optical transceiver. According to the different transmission media, there are single-mode optical terminals and multimode optical terminals.
The digital optical transceiver digitizes the image, voice and data signals to be transmitted, and then multiplexes these digital signals, thereby converting a plurality of low-speed digital signals into a high-speed signal and converting this signal into an optical signal. At the receiving end, optical signals are converted into electrical signals, and the converted high-speed signals are decomposed into original multi-channel low-speed signals, and finally these data signals are converted into image, voice and data signals. Analog optical transceiver modulates the amplitude or frequency of the signal to be transmitted, and then converts the modulated electrical signal into an optical signal. At the receiving end, the optical signal is reduced to an electrical signal, and then the signal is demodulated to recover the image, voice or data signal.
The signal quality of digital optical transceiver is high, without the disadvantages of serious cross modulation interference, easy environmental influence, poor transmission quality and poor long-term working stability when analog FM, PM and AM optical transceivers transmit multiple signals at the same time. Therefore, digital optical transceiver will gradually replace analog optical transceiver.
In the multi-purpose and monitoring system of optical transceiver, when the transmission distance of coaxial cable is not enough, optical transceiver can be used for optical cable transmission. The optical transceiver can transmit not only video signals, but also audio signals, that is, the video/audio signals at the scene are transmitted to the control center together. The most common example of using optical transceivers is the monitoring of intersections. Usually these cameras are several kilometers away from the control center. When copper cable and amplifier can't reach the distance, optical transceiver can be used for optical cable transmission.
At present, optical terminals such as video, image, audio, data and Ethernet have been widely used in expressway, traffic, electronic police, monitoring, security, industrial automation, electric power, customs, water conservancy, banking and other fields. When choosing an audio transceiver, users will generally consider its first pass parameters and practicality, and the relevant parameters are specified in the transceiver's factory manual. Again, let's talk about the choice of audio transceiver from a practical point of view.
1, generous in appearance and reasonable in structure.
Audio optical transceiver has high technical content, exquisite and elegant appearance, and the overall structure should meet the requirements of engineering installation as far as possible. General indoor digital video optical transceiver not only adopts 19-inch cabinet, but also can meet the needs of putting optical transceiver on desktop or wall in engineering. Digital optical transceiver In addition, audio optical transceiver must also have good heat dissipation performance and electrical contact performance.
2. Rich interface and reasonable layout.
In addition to adequate video interfaces, audio optical terminals may need or be required to be equipped with other interfaces with rich functions in the future, such as high-definition audio interface, telephone interface, asynchronous data interface, Ethernet interface and switch interface. This requires that the selected digital video transceiver must have the ability to upgrade the system, so as to avoid completely replacing the equipment due to network upgrade or system function change, thus protecting the user's upfront investment. There are many types of telephone optical transceiver interfaces. There are many interfaces, and there may be some modes to set dip switches. The user interface composed of all these elements should be reasonably laid out, and there should be considerable operating space between interfaces, which is convenient for engineering installation and maintenance. For example, if the video interfaces are too dense, there will be an embarrassing situation that other normal video interfaces must be unplugged in order to maintain one video interface in practical application.
3. The indicator light has a clear meaning, which is convenient for project opening and maintenance.
In order to facilitate the opening and maintenance of the project, the telephone optical terminal should be marked with obvious indicator lights. In addition to the power indicator, the transceiver of digital video optical transceiver must also have a video indicator to indicate whether the corresponding video channel has video signal input or output. Engineers and users can judge the opening and maintenance situation according to the instructions of the video indicator in the engineering opening stage and engineering maintenance stage, locate the fault point and solve the possible problems as soon as possible. When choosing an audio transceiver, we should not only pay attention to its parameters and practicability, but also pay attention to its after-sales service. If the after-sales service of the selected brand is not in place, the maintenance and inspection when the transceiver fails will be relatively troublesome, which will bring great changes to the project.
Some foreign brands (in no particular order):
NTK, Infineon, ANV, Divvy, BIC, CWY, STV, MRD, OSD, OPTILINKS, PELCOOPTELECOM, Meridian (Meridian), Siemens (Siemens), Alcatel, Yatu, etc.
Some domestic brands (in no particular order)
Optical Network Vision (ONV), Beijing Sunshine Hua Yao, Northern Network Communication, Chengdu Harley, Ante Video, Chengdu Anshi, Songtuo Network, Shenzhen Lailai, Chengdu Anshi, Xunwei, Guangzhou Yin Xun, Shiqiao Optical Network, Xinchuang, Hualong, Optel, WINGMAX, Beijing AOBO Photoelectricity (AOBO) and Beijing Huaxing Yi Electronics.