Scheme design of wireless monitoring system in factory area

The video monitoring system is mainly composed of camera, wireless video transmission, display and recording, remote control management and TV wall display. Wireless monitoring refers to a monitoring system that uses radio waves to transmit video, sound, data and other signals without wires (cables).

Advantages of wireless monitoring:

1), with low comprehensive cost and more stable performance. Only one-time investment is needed, and it is not necessary to dig trenches and bury pipes, which is especially suitable for outdoor places and decoration occasions with a long distance; In many cases, users are often limited by geographical environment and work content, such as special geographical environment such as mountains, ports and open areas, which brings great inconvenience to the wiring project of wired network and wired transmission, and the construction period of using wired will be very long or even impossible. At this time, wireless monitoring can get rid of the shackles of cables, and has the advantages of short installation period, convenient maintenance, strong capacity expansion and fast cost recovery.

2), flexible networking, good scalability, plug and play. Managers can quickly add new wireless monitoring points on the existing network, without laying the network or adding equipment for new transmission, and easily realize remote wireless monitoring.

3) Low maintenance cost. Wireless monitoring and maintenance is maintained by the network provider, and the front-end equipment is a plug-and-play maintenance-free system.

4) Wireless monitoring system is a combination of monitoring and wireless transmission technology. It can transmit the field information from different places to the wireless monitoring center in real time by wireless communication means, and automatically form a video database for future retrieval.

5) In the wireless monitoring system, the wireless monitoring center needs to obtain the video information of monitoring points in real time, and the video information must be continuous and clear. In wireless monitoring points, cameras are usually used to collect the scene in real time. The camera is connected through video wireless transmission equipment and sends data signals to the monitoring center through radio waves.

Transfer content

The information content that each monitoring point needs to transmit to the monitoring room, that is, in addition to image information, whether it is necessary to transmit data information such as sound signals and wireless command control (cloud mirror control).

Mode of operation

In the wireless monitoring system, the image system generally adopts one-to-one working mode or point-to-point working mode, that is, one transmitter corresponds to one microwave receiver, 10 monitoring points need 10 microwave transmitters and 10 microwave receivers at the receiving end, which is mainly determined by the display mode of the system image.

As far as the control system is concerned, there is generally only one control host, such as hard disk video recorder or matrix, and there are many decoders. Therefore, the control system generally works in the one-point multiple access mode. Whether you have 1 monitoring points or 100 monitoring points, you only need one remote control command transmitter, and the number of remote control command receivers depends on the number of ptz and lens to be controlled.

The wireless transmission part is the image signal channel of the system. The wireless transmission system consists of two parts: wireless microwave video transmission system and wireless command and control system. Wireless microwave video transmission system: used to transmit video, and the images collected by the camera are transmitted to the monitoring center through wireless microwave. Wireless command and control system: If you need to control the ball, pan/tilt and lens, you need to use the wireless command and control system. This monitoring method has the advantages of clear image, no delay, no compression loss, low cost, simple construction, installation and debugging, etc., and is suitable for occasions with few monitoring points and few relays.

Wireless microwave video transmission system;

Close range: the front-end monitoring image is modulated by HD-680 microwave transmitter, and then the microwave signal is transmitted to the monitoring center through the antenna. The monitoring center receives the microwave signal received by the antenna, demodulates it by the HD-680RX microwave receiver, and directly outputs the image signal to the monitor. (See the picture for details)

Remote: schematic diagram of HD-630 series wireless microwave transmission monitoring system;

Wireless command and control system;

Close range: The monitoring center of wireless command and control part consists of command and control antenna, HD-2080 wireless command and control transmitter, control keyboard/hard disk video recorder/matrix, and the front end consists of HD-2090 wireless command and control receiver and command and control antenna. (See the picture for details)

Long-distance: schematic diagram of HD-2050 series and HD-2060 series wireless command and control system;

Lightning protection measures for wireless equipment

For general buildings, the methods to avoid lightning strike mainly include:

(1) Dredge, that is, divert the charges in the thundercloud to the earth, so as to avoid direct lightning strike or induced lightning strike current flowing through the protected buildings or equipment, thus protecting these buildings or equipment from lightning strike.

(2) Isolation, that is, the lightning signal is isolated from the protected object to avoid lightning strike.

(3) Equipotential, that is, the ground of the tower, the workplace and the public ground of the building are placed at the same potential.

(4) Dissipation, that is, releasing opposite charges to neutralize the charges in the thundercloud, thus preventing the formation of lightning. According to the above lightning strike communication equipment, combined with the lightning protection method of buildings, the main lightning protection measures are as follows for the lightning protection design of a wireless communication project.

Install lightning rod or lightning protection device

The lightning protection measures of most wireless devices are mainly to install lightning rods on communication towers. This method is economical and simple, but it should be installed in strict accordance with the following requirements. The lightning rod should be installed several meters above the tip of the antenna, and there should be a certain interval between the lightning rod and the antenna to prevent the radiation pattern of the antenna from being damaged due to the existence of the lightning rod and affect the communication effect. The general practice is that the lightning rod becomes the main pole of the antenna tower, but the communication antenna is installed outside the lightning rod about 15 wavelength. The resistance of DC path of lightning protection ground wire should be low enough, generally10 ~ 50Ω. Due to the large lightning impulse current, wide frequency spectrum and short duration, the inductance is required to be as small as possible. Flat braided wire or stranded wire cannot be used for ground wire, because this kind of wire has large inductance, which is not conducive to lightning current discharge and is easy to be corroded. As far as possible, use a solid conductor of more than 3 mm, and it is best to use the same metal material. In order to increase the surface drainage area, several grounding bodies can be buried at certain intervals and welded to each other. For example, about 1 0 copper pipes were buried around the building at a distance of1to 2 meters and welded.

Although it is economical and simple to install lightning rod on communication tower, it is difficult to be foolproof. For some important communication projects, we can consider installing radioactive lightning protection devices. Radioactive lightning protection device can be said to be one of the most advanced lightning protection devices in the world. The key part of radioactive lightning protection device is radioactive source, which can emit alpha particles continuously by itself and ionize the surrounding air to produce a large number of electrons. Under the action of lightning field, these electrons are accelerating continuously, resulting in chain multipole ionization or avalanche ionization of air, forming an electron flow proportional to the electric field strength. At this time, the ionization conductance generated by the radioactive source pointing to Lei Yun will neutralize and release the space charge forever, eliminate the existing low electric field, and reduce the possible high electric field to a low electric field, thus effectively preventing lightning strikes and playing a significant role in lightning suppression. This radioactive lightning protection device has a large protection area and a radius of about 260 meters, which is safe, reliable and harmless to people.

Install lightning arrester

In addition to installing lightning rods or lightning protection devices on communication towers, attention should also be paid to eliminating induced lightning. The usual practice is to install lightning arrester in the antenna feed system.

When installing lightning arrester in antenna feeder system, the following problems should be paid attention to. First of all, the grounding terminal of lightning arrester must be reliably connected with the ground, and the grounding resistance should not be greater than 5Ω, otherwise the lightning protection effect will be affected. Second, the lightning arrester has a certain insertion loss, which has a certain impact on the intensity of antenna radiation signals. At the same time, we should pay attention to the change of standing wave ratio. Generally, the standing wave ratio of the antenna feed system is required to be less than or equal to 15. 3. When installing the communication antenna, the antenna support rod should be reliably connected with the tower, and the connection resistance is equal to zero. Feeders should hang down from the inside of the tower and be fixed with copper wires at regular intervals. For important communication projects, besides installing lightning arresters in the antenna feeder system, attention should also be paid to the lightning protection of the power supply system. The general practice is to install lightning protection devices in transformers and distribution rooms.

Setting pressure balance belt

Laying a pressure equalizing belt around the roof of the communication room, and connecting it with the horizontal closed grounding belt laid outdoors around the communication room through more than two down leads. There are at least two connections between the outdoor horizontal closed grounding belt and the communication equipment grounding network. The purpose of this is to make the lightning current evenly distributed and reduce the possible induced overvoltage.

Natural grounding body

In modern high-rise buildings, the reinforced concrete of the building is used as the grounding body, and the metal water supply and drainage pipeline is used as the natural grounding body, so the area of the grounding grid is quite large. Using it to guide lightning into the ground can not only greatly weaken the transient electromagnetic field when lightning invades, but also act as a metal shield to weaken the invasion of electromagnetic pulse. At this time, the operation mode of * * * is adopted, which is more conducive to the safety of human body and communication equipment. Grounding resistance should be less than or equal to 1ω.

In non-reinforced concrete buildings, the ground operation mode should be adopted, the mutual distance between grounding devices is generally greater than 20m, and the grounding resistance should be considered as 2 ~10Ω according to the actual situation.

Reasonable arrangement of all kinds of grounding

The grounding system of communication equipment can be generally divided into: lightning protection grounding, AC power working grounding, safety protection grounding, DC working grounding system, etc. The purpose of shielding and lightning protection measures is to prevent space electromagnetic wave induction, overvoltage and magnetic field energy from invading the protected communication equipment, and to suppress and eliminate the interference and harm of electromagnetic fields. In short, accidents such as communication interruption, computer network paralysis and equipment damage caused by lightning overvoltage occur from time to time, which is extremely harmful to the national economy. Lightning overvoltage and electromagnetic interference protection of communication facilities is an important technical means to protect the safety of communication lines, equipment and people, an indispensable technical link to ensure the operation rate of communication lines and equipment, and an important part of communication network construction and operation management. According to GB 50057-94 Code for Lightning Protection Design of Buildings and JGJ/T 16-92 Code for Electrical Design of Civil Buildings, the grounding electrode of all equipment in the control room and the metal shell of the equipment are grounded. The specific treatment method of grounding is: lead a branch line from the main line of the same grounding body to the central computer room, and install a bus in the computer room. Power grounding, anti-static grounding, lightning protection grounding and equipment shell grounding respectively lead the grounding wire to the bus bar and connect it firmly to ensure the safety of electrical equipment and people.