How to Choose the Right Multiservice Video Optical Transceiver in Security Surveillance Engineering

Optical transceivers have evolved along with the development of the surveillance industry, from analog to digital, from digital to high-definition, step by step, after so many years of technological accumulation, has developed to a very mature stage; Beijing frogvision communications technology limited liability company technology Director Yao Zhihong said: For the moment, optical transceivers do not have much technical breakthroughs, but in the subdivided applications, some special functions can still be developed and improved, including the improvement of conventional performance such as system stability and capacity. Optical manufacturers are also tirelessly seeking breakthroughs.

Currently, there are many kinds of multi-channel video optical transceivers on the market, and there are countless technical indicators involved. Most of the engineering vendors and users lack the corresponding means to judge the rationality and authenticity of technical indicators. Therefore, it is easy to lose direction when selecting multiple video optical transceivers. . This article describes two technical indicators that are easy to verify and relatively critical in engineering, and focuses on practicality and reliability, and analyzes how to properly select multiple video optical transceivers in security monitoring projects.

one. Technical considerations

Multiple video optical transceivers can have multiple functions, and each type of function has corresponding technical indicator requirements, such as video indicators, audio indicators, asynchronous data indicators, Ethernet indicators, and so on. Specific technical indicators can require manufacturers to provide third-party test certificates. Conditional contractors should conduct retesting in accordance with manufacturer-supplied specifications before purchasing equipment to verify the actual technical specifications of the equipment and the integrity of the manufacturer. Here, the following two video indicators are briefly described from the engineering point of view.

1, APL range is wide enough

APL, the average level of the image, many builders do not pay much attention to or are not familiar with this indicator. However, if we talk about a problem encountered in some projects: the video signal is transmitted by the optical transceiver, when the screen has a large area of ​​white (such as when the camera is illuminated by a strong light) the monitor will horizontally shake, then The engineering staff is no stranger to it. 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 image signal increases, and the APL will increase, resulting in a decrease in the horizontal synchronization signal amplitude. Or, the monitor cannot detect line synchronization and screen jitter occurs.

2, 3dB video bandwidth is enough

Video bandwidth is an old growth issue. With insufficient video bandwidth, the details of the monitor screen are not clear enough, the horizontal resolution is low, and even serious color distortion or loss occurs. It is because of the importance of video bandwidth to image quality that some unscrupulous manufacturers intentionally exaggerate the video bandwidth of the product to deceive customers. A multi-channel digital video optical transceiver produced by a manufacturer claims its video bandwidth is 8M, but its externally announced video sampling frequency is 12.5M. In accordance with the Nyquist sampling law, to truly restore the signal, the sampling frequency should be at least twice the signal frequency. In this way, the theoretical video bandwidth of the optical transceiver of this manufacturer cannot exceed 6.25M in any case. Obviously, this is a lie that exaggerates the performance of deceiving customers, so that manufacturers with no commercial reputation should not be considered for inclusion in the scope of purchase. However, not all customers are able to accurately identify manufacturer's lies. For general contractors and users, the device's video bandwidth can be roughly judged by observing the details of the image.

two. Reliability considerations

As a security monitoring project, equipment reliability should be the first consideration. The reliability of the equipment is the equipment manufacturer must consider when designing the product, however, some manufacturers may be unwilling to do or do not know how to do this work for some reasons. Here, the following issues are briefly discussed from the engineering perspective.

1, easy power supply, wide power range

Power supply is the primary consideration for ensuring the reliability of digital video optical transceivers. Power supply cannot be guaranteed to be reliable and reasonable. Talking about the reliability of digital video optical transceivers, it becomes a matter of time. The video optical transceiver with 220VAC power supply is more convenient and reliable, and the optical transceiver of 220VAC power supply should be selected as much as possible in the project. This type of optical transceiver currently has two main power supply methods. One is an external power supply type, and the other is a power supply internal 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 has high reliability. Therefore, current multi-channel digital video optical transceivers mostly use built-in power supplies.

Based on the situation of the domestic power grid and combined with the actual site conditions, a multi-channel digital video optical transceiver with a wide input power range should be selected as much as possible. Generally, the optical transceiver using switching power supply should be selected as much as possible. Compared with the linear power supply, the switching power supply is not only highly efficient, but also has a wide input voltage of the switching power supply, which can basically guarantee the normal operation within the range of 160VAC~265VAC, and its output voltage will not change with the input voltage, and thus will not affect the optical transceiver. Work performance and technical indicators will not cause the optical transceiver to start repeatedly due to instability of the power grid and interrupt the transmission of monitoring video and audio signals.

2, port protection

The video port, audio port, and data port of the optical transceiver are extremely vulnerable to damage. Static electricity, surges, and induced lightning strikes may cause damage to the optical port. In addition to the construction, the equipment itself must be handled carefully. The necessary port protection should be provided. When selecting the optical transceiver, special attention should be paid to the vendor's port protection measures.

3, temperature, humidity and strong adaptability

In some security monitoring projects, the working conditions of the optical transceivers are rather poor, the temperature range is wide, and the air humidity is high. Occasionally, some field monitoring points will also lose power, and the optical transceivers will heat up when they work. When the power is turned off, there will be condensation beads when the equipment is cooled. All of these require multiple digital video transceivers to have more consideration in the temperature range and allowable humidity, so as to ensure that they can work stably in harsh environments and adapt to security monitoring needs.

4, grounding considerations

In the security monitoring project, ensuring the good grounding of the equipment is an important link to ensure the reliability of the equipment. A good grounding will benefit the device against surge surge, anti-static and lightning strikes, which can significantly improve the reliability of the equipment. Therefore, when selecting optical transceivers, special attention should be paid to the manufacturer's grounding plan, and thus the strength of the manufacturers can also be seen. A good grounding should have the following considerations:

First, the power supply of the optical transceiver must be grounded. As an industrial-grade product, for the safety of equipment and personnel, multi-channel digital video optical transceivers should be connected to the power socket using the national standard 220VAC power cord, and cannot be connected to the power socket in order to save trouble. In addition, the grounding of the power socket should be reliably connected with the earth in the project.

Secondly, the RS485 data terminal of the multi-channel digital video optical transceiver should also provide a grounding cable to connect with the ground terminal of the peer device in the project, so as to avoid damage to the data port due to the ground potential difference between the devices at both ends of the RS485 channel.

Finally, the signal terminal of the optical transceiver should be connected to the chassis ground and the earth to provide a bleeder circuit for the accumulated static charge to prevent static charge accumulation and damage the equipment. The good connection between the signal terminal of the optical transceiver and the chassis ground and earth can effectively prevent the damage caused by the induced lightning to the equipment.

three. Practical considerations

Each vendor should provide mature products to users and contractors, not research prototypes. Therefore, it must have practical considerations. When selecting optical transceivers, users and engineers can take more considerations from the perspective of the practicality of the equipment. First, practical problems are easy for users and engineers to judge. Second, it is difficult to believe that manufacturers who can't do a good job can do a good job on the reliability and technical indicators of their optical transceivers. Here we will briefly discuss the practicality of the optical transceiver from the following perspectives.

1. Appearance, reasonable structure

The multi-channel digital video transmitter and receiver has a high technical content, and its appearance should be small and exquisite, elegant and generous, and the overall structure must meet the requirements of engineering installation as much as possible. General indoor multi-channel digital video optical transceivers, in addition to using 19 width to fit in the standard 19 cabinet, should also take into account the needs of the projector placed on the desktop or wall. In addition, multi-channel digital video transceivers must also have good thermal performance and electrical contact performance.

2, rich interface, reasonable layout

In addition to requiring sufficient video interfaces, multi-channel digital video transceivers may require or may require other interface with rich functions, such as high-fidelity audio interfaces, ordinary telephone interfaces, asynchronous data interfaces, Ethernet interfaces, and digital interfaces, etc. This requires that the selected multi-channel digital video optical transceivers must have system upgrade capability so that they do not completely replace the equipment due to network upgrades or system function changes, thereby protecting the user's upfront investment.

There are many kinds of multi-channel digital video optical transceiver interfaces, and there are a large number of interfaces. There may be some modes to set the dial switch. The user interface formed by all these elements should be reasonably laid out, and there should be considerable space for operation between interfaces to facilitate the project. Installation and maintenance. For example, the video interface is too intensive, and in real applications, there will be an awkward situation in which a normal video connector must be unplugged to repair a video connector.

3, the video can be on the next, convenient network

In some security monitoring projects, there are multiple video lines along the route of an optical fiber to be transmitted to the central monitoring room. On the other hand, some security monitoring projects are the opposite of the former. One or more video signals are transmitted to various receiving points along the optical fiber. There are security monitoring projects, multi-channel video signals need to transmit a very long distance, in the middle may need to use several relays. This requires multiple digital video transceivers to have video signal insertion and extraction functions and lossless relay functions (relay signals directly at the transport layer instead of relaying signals at the user interface layer, which will degrade the technical specifications of the video signal). Stronger manufacturers have not only provided such products, but also provided products that cross-connect between any video path signals, any audio path signals, and any data path signals, and have already applied them. If there are such requirements in the project, priority should be given to the use of such equipment, which not only reduces the number of points of failure, increases the reliability of the system, guarantees technical indicators, but also reduces engineering costs and saves user investment.

4, the indicator light clear, easy to open and maintain the project

In order to facilitate the opening of the project and the maintenance of the project, multiple digital video transmitters should be marked with clearly defined indicators. In addition to the power indicator, multiple transceivers for digital video transceivers must have video presence or absence to indicate whether the corresponding video channel has input or output video signals. Engineering personnel and users are involved in the engineering startup phase and project maintenance phase. According to the indication of the video indicator, the situation during the opening and maintenance can be judged, the fault point can be located, and possible problems can be solved as soon as possible.

In addition, for the audio and data sections, corresponding indicators should also be provided. The simple way is to refer to the telecommunication equipment's practice and provide the synchronization indicator and the loop indicator. According to this, the engineering personnel and the equipment manufacturer can judge whether the equipment system is faulty or the interface is partially faulty, so as to make a correct response.

For Ethernet interfaces, connection/activity indicators, full/half duplex indicators, and 10M/100M indicators should be provided in accordance with the general requirements for data communications equipment.

Multi-channel digital video transceivers shall also provide system indicators to indicate whether the sending device is normal and whether the receiving device is normal, so as to make it easier for engineers to distinguish whether the device is faulty or the optical fiber link is faulty.