At present, the multi-channel digital + video optical transceiver on the market involves a wide variety of technical indicators. Most projects and users lack the corresponding means to judge whether the technical indicators are reasonable and true. Therefore, it is easy to get lost when choosing products. Today, the editor of Feichang Technology describes the key and easy-to-verify technical indicators in security engineering from two aspects, and focuses on reliability and practicability, and analyzes how to choose multiple channels in security monitoring engineering. Digital video optical transceiver. If you are interested, let's take a look!
1. Technical index considerations
Multi-channel digital video optical transceivers can have multiple functions, and each type of function has corresponding technical index requirements, such as video index/audio index/asynchronous data index/Ethernet index, etc. Specific technical indicators can require the manufacturer to provide a third-party test certificate. For conditional projects, retest should be carried out in accordance with the indicators provided by the manufacturer before purchasing equipment to check the actual indicators of the equipment and the integrity of the manufacturer.
1.13db video broadband is enough
Video bandwidth is a commonplace issue. Insufficient video bandwidth, the details of the monitoring torus are not clear enough, the horizontal resolution is low, and serious color distortion may even occur. It is precisely because of the importance of video bandwidth to image quality that unscrupulous European Union manufacturers deliberately exaggerate the video bandwidth of their products to deceive customers. The multi-channel digital video produced by a certain manufacturer has this functional segment and claims that its bandwidth is 8m, but its publicly announced video sampling frequency is 12.5m. According to the Nyquist sampling theorem, to truly restore the signal, its sampling frequency should be at least twice the signal frequency. In this way, the theoretical video bandwidth of this manufacturer's optical transceiver cannot exceed 6.25m in any case. Obviously, this is a lie to deceive consumers with exaggeration, so that manufacturers without business reputation should not be included in the scope of purchase. However, not all customers can accurately identify the lies of the manufacturer. For general engineering companies and users, they can roughly judge the video bandwidth of the device by observing the details of the image.
1.2 APL range is wide enough
APL, that is, the average level of the image, many engineering companies are not paying attention to or familiar with this indicator. However, if we talk about 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 screen, the screen of the monitor manufacturer will jitter horizontally, then the engineer must be familiar with it. Because the APL range of the video optical transceiver produced by the manufacturer is too narrow, when there is a large area of white in the image signal, the DC component of each line of the image signal will increase and the APL will increase, resulting in the reduction or loss of the horizontal synchronization signal symbol. The monitor cannot detect line synchronization and the screen shakes.
2. Reliability considerations
As a security monitoring project, the reliability of equipment should be the first consideration. The reliability of equipment is what equipment manufacturers need to consider when designing their products. However, some manufacturers may be unwilling to do or do not know how to do this work for some reasons. Here focuses on briefly discussing these issues from an engineering perspective.
2.1 Power supplier Bo Ni, wide power supply range
The primary consideration for ensuring the reliability of digital video optical transceivers when supplying power is that the power supply cannot be guaranteed to be reliable/reasonable. Talking about the reliability of digital video optical transceivers becomes a fish in the water. Optical transceiver with 220VAC power supply. This kind of optical transceiver currently has two main power supply modes, one is the external power supply, and the internal power supply, that is, the power supply and the optical transceiver are integrated. From the engineering application point of view, the built-in power supply is not only easy to install, but also highly reliable. Therefore, most of the current multi-channel digital video optical transceivers adopt the built-in power supply.
Based on the domestic power grid situation, combined with the actual project site, a multi-channel digital video optical transceiver with a wide input power range should be selected as far as possible. Generally, optical transceivers with switching power supplies should be selected as far as possible. Compared with the linear power supply, the switching power supply is not only efficient, but also has a wide input voltage. It can basically guarantee normal operation in the range of 160VAC-265VAC, and its output voltage will not change with the voltage change, so as not to affect the operation of the optical transceiver Performance and technical indicators will not cause repeated start-up of the optical transceiver due to the unstable power grid, interrupting the transmission of monitoring video/audio signals.
2.2 High temperature/humidity adaptability
In some security monitoring, the working conditions of the optical transceiver are relatively harsh, the temperature change range is wide, and the air humidity is high. Some field monitoring points will occasionally have power outages, and the optical transceiver will work hot, and there will be water droplets when the equipment is cooled during a power outage. This requires the multi-channel digital video optical transceiver to have more consideration in terms of temperature range and allowable humidity to ensure that it can work stably in harsh environments and meet the needs of security monitoring.
2.3 Grounding considerations
In the security monitoring project, it is an important link to ensure the reliability of the equipment when ensuring the good grounding of the equipment. Good grounding is good for equipment to withstand surge, anti-static and anti-lightning, and can significantly improve equipment reliability. Therefore, when choosing an optical transceiver, you should pay attention to the manufacturer's grounding plan, which can also show the manufacturer's strength:
① The power supply of the optical transceiver must be grounded. As an industrial-grade product, for the safety of equipment and personnel, the multi-channel digital video optical transceiver should be connected to the power socket with the national standard 220VAC power cord, instead of using a two-core power cord to connect to the power socket in order to save trouble. Moreover, in the project, it should be ensured that the ground wire of the power socket is reliably connected to the earth.
②The signal ground of the optical transceiver should be connected to the chassis ground/earth to provide a discharge circuit for the accumulated static charge to prevent static charge accumulation and equipment damage. A good connection between the signal ground of the optical transceiver and the chassis ground/earth can effectively prevent damage to the equipment caused by the induction mine.
③The RS485 data terminal of the multi-channel digital video optical transceiver should also provide a ground wire to connect to the ground terminal of the opposite device in the project to avoid damage to the data port due to the ground potential difference between the devices at both ends of the RS485 channel.
2.4 Port protection
The video port/video port/data port of the optical transceiver is extremely vulnerable to damage. Static electricity/surge/inductive lightning strikes may cause damage to the optical transceiver port. In addition to the construction requirements, the equipment itself should also be carefully operated in strict accordance with the construction requirements. The necessary port protection should be provided. When choosing an optical transceiver, special attention should be paid to the manufacturer's port protection measures.
3. Practical considerations
What each manufacturer provides to users and engineers should be mature products, not scientific research prototypes, so it must have practical considerations. When choosing an optical transceiver, users and engineering companies can consider more from the perspective of the practicability of the equipment. First, users and engineering companies can easily judge the problems of practicability; second, it is difficult to believe that manufacturers who cannot do well in practicability can do well in the reliability and technical indicators of optical transceivers.
Well, the above content is the relevant introduction of Feichang Technology on the selection of optical transceivers in the security monitoring project. I hope it can be helpful to everyone! Feichang Technology has been specialized in the R&D, production and sales of industrial communication equipment such as optical transceivers, industrial switches, optical fiber transceivers, and protocol converters for 20 years. Welcome to come to understand and exchange.