At present, multi-channel digital video optical transceivers on the market involve a wide variety of technical indicators. Most engineering companies and users lack the corresponding means to judge the rationality and authenticity of technical indicators, so it is easy to lose direction when selecting products. This paper describes two technical indicators that are relatively critical and easy to verify in engineering, and focuses on how to select multi-channel digital video optical transceivers in security monitoring engineering from the perspective of availability and practicality.
1. Technical indicators
Multi-channel digital video optical transceivers can have a variety of functions, each type of function has corresponding technical indicators, such as video indicators, audio indicators, asynchronous data indicators, Ethernet indicators and so on. Specific technical indicators may require manufacturers to provide third-party test certificates. Conditional engineering companies should re-test according to the indicators provided by the manufacturers before purchasing equipment to verify the actual technical specifications of the equipment and the integrity of the manufacturers. Here we focus on the following two video indicators from an engineering perspective.
1.1 3db video bandwidth is sufficient
Video bandwidth is an old growing issue. The video bandwidth is insufficient, the details of the monitor picture are not clear enough, the horizontal resolution is low, and even the color distortion or loss occurs. Because of the importance of video bandwidth to image quality, some unscrupulous vendors deliberately exaggerate the video bandwidth of their products to deceive customers. A multi-channel digital video optical transceiver produced by a manufacturer claims that its video bandwidth is 8m, but its externally announced video sampling frequency is 12.5m. According to Nyquist's law of sampling, to truly restore the signal, the sampling frequency should be at least twice the signal frequency. In this way, the theoretical video bandwidth of this manufacturer's optical transceiver may not exceed 6.25m in any case. Obviously, this is a lie that exaggerates performance to deceive customers, so that vendors without commercial reputation should not be considered for purchase. However, not all customers can accurately identify the manufacturer's lies. For general engineers and users, by observing the details of the image, the video bandwidth of the device can be roughly judged.
1.2 apl range is wide enough
Apl, the average level of the image, many engineers pay little attention or are not familiar with this indicator. However, if you have a problem encountered in some projects: the video signal is transmitted through the optical transceiver, when there is a large area of ​​white in the picture (such as when the camera is illuminated by strong light), the picture on the monitor will horizontally jitter, then Engineers must be familiar. This is because the apl range of video optical transceivers produced by some manufacturers is too narrow. When there is a large area of ​​white in the image signal, the DC component in each line of image signals increases, and apl will increase, resulting in a reduction in the amplitude of the line sync signal. Or lost, the monitor cannot detect the line sync and the picture is shaken.
2. *ability consideration
As a security monitoring project, the availability of equipment should be the first consideration. The availability of equipment is something that equipment manufacturers must consider when designing their products. However, some vendors may be reluctant to do or do not know how to do this for some reason. The focus here is on the following issues from the engineering perspective.
2.1 Power supply is convenient, the power supply range is wide
Power supply is the primary consideration for ensuring the reliability of digital video optical transceivers. Power supply cannot be guaranteed to be * reasonable, and the reliability of digital video optical transceivers has become a fishing in the water. The video optical transceiver powered by 220vac is convenient to take power, and the quality is also high. In the project, the optical transceiver of 220vac power supply should be selected as much as possible. At present, the optical transceiver mainly has two power supply modes, one is a power external type, and the other is a power built-in type, that is, the power supply and the optical transceiver are integrated. From the perspective of engineering applications, the built-in power supply is not only easy to install, but also highly versatile. Therefore, most of the current multi-channel digital video optical transceivers are built-in power supply.
Based on the domestic power grid situation, combined with the actual project site, multi-channel digital video optical transceivers with a wide input power range should be selected. Generally, you should choose the optical transceiver that uses the switching power supply. Compared with linear power supply, switching power supply is not only efficient, but also has a wide input voltage of switching power supply. It can basically guarantee normal operation in the range of 160vac-265vac, and its output voltage will not change with the input voltage, so it will not affect the optical transceiver. The performance and technical indicators will not cause the optical transceiver to restart repeatedly due to the instability of the power grid, interrupting the transmission of surveillance video and audio signals.
2.2 High temperature and humidity adaptability
In some security monitoring projects, the working conditions of the optical transceiver are relatively harsh, the temperature variation range is wide, and the air humidity is large. Some field monitoring points will occasionally lose power, and the optical transceiver will be hot when working. When the equipment is powered off, there will be condensation water droplets during cooling. All of these require multi-channel digital video optical transceivers to have more considerations in terms of temperature range and allowable humidity to ensure stable operation in harsh environments and to meet security monitoring needs.
3.1 Appearance and reasonable structure
The multi-channel digital video optical transceiver has high technical content, and its appearance should be small and exquisite, beautiful and elegant, and the overall structure must meet the engineering installation requirements as much as possible. In general, the indoor multi-channel digital video optical transceiver should also take into account the need to place the optical transceiver on the desktop or the wall in addition to the 19 伎 纫 å… å… æ²§ 沧 诒曜 诒曜 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 In addition, multi-channel digital video optical transceivers must also have good thermal performance and electrical contact performance.
3.2 rich interface, reasonable layout
In addition to requiring sufficient video interfaces, multi-channel digital video optical transceivers may require or may require other feature-rich interfaces, such as high-fidelity audio interfaces, ordinary telephone interfaces, asynchronous data interfaces, Ethernet interfaces, and digital interfaces. This requires that the selected multi-channel digital video optical transceiver must have the system upgrade capability, and will not completely replace the equipment due to network upgrade or system function change, thus protecting the user's upfront investment.
There are many types of multi-channel digital video optical transceivers, and there are many types of mode setting dial switches. The user interface of all these elements should be laid out reasonably, and there is considerable operation space between the interfaces to facilitate engineering. Installation and repair. For example, the video interface is too dense. In actual applications, there will be an embarrassing situation in which one video connector must be removed and other normal video connectors must be unplugged.
3.3 The meaning of the indicator light is clear, which facilitates the opening and maintenance of the project.
In order to facilitate project opening and engineering maintenance, multi-channel digital video optical transceivers should be marked with clear-cut indicators. In addition to the power indicator, the transceiver of the multi-channel digital video optical transceiver must have a video indicator or not to indicate whether the video channel has video signal input or output. The engineers and users are in the project opening phase and engineering maintenance phase. According to the indication of the video indicator, you can judge the situation during opening and maintenance, locate the fault point, and solve the problem that may occur as soon as possible.
In addition, for the audio and data sections, the corresponding indicator light should also be provided. The simple way is to refer to the practice of telecommunication equipment, provide synchronous indicator lights and loop indicator lights, and engineers and equipment manufacturers can judge whether the equipment system is faulty or the interface part is faulty, so as to make a correct response.
For Ethernet interfaces, connection/activity indicators, full-duplex/half-duplex indicators, and 10m/100m indicators shall be provided in accordance with the general requirements of data communication equipment.
The multi-channel digital video optical transceiver should also provide a system indicator to indicate whether the sending device is normal and whether the receiving device is normal, so that the engineering personnel can distinguish whether the device is faulty or the fiber link is faulty.
In summary, when selecting a device, the user can consider the technical indicators, operability, and practicability of the device. According to the above methods, compare and compare according to the actual situation of the project, and finally find the most. Suitable for your own multi-channel digital video optical transceiver.
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