Weak current project
According to the strength of power transmission power, electric power applications can be divided into two categories: strong power and weak power. The electricity consumption of buildings and buildings generally refers to the strong electricity of AC 220V50Hz and above. It mainly provides electric energy to people and converts electric energy into other energy sources, such as air-conditioning electricity, lighting electricity, power electricity and so on.
There are two main types of weak electricity in intelligent buildings. One is low-voltage electric energy such as the safety voltage level and control voltage stipulated by the state. Back-up power for lights. The other type is information sources that carry information such as voice, images, and data, such as information from telephones, televisions, and computers. People are used to referring to weak current technology as weak current technology. It can be seen that the basic meaning of weak current technology for intelligent buildings is still weak current technology in the original sense. However, with the rapid development of modern weak current high-tech, the application of weak current technology in intelligent buildings is becoming more and more extensive.
In general, weak current system engineering refers to the second type of application. mainly include:
- TV signal engineering, such as TV monitoring system, cable TV.
- Communication engineering, such as telephone.
- Intelligent fire protection engineering.
- Sound reinforcement and sound engineering, such as medium and background music broadcasting in residential areas, and background music in buildings.
- Integrated wiring engineering, mainly used for computer network.
With the rapid development of computer technology, the rapid enhancement of software and hardware functions, and the perfect combination of various weak current system engineering and computer technology, the various classifications in the past are no longer as clear as before. The mutual integration of various projects is system integration. ?
Common working voltages of weak current systems include: 24VAC, 16.5VAC, 12VDC. Sometimes 220VAC is also considered a weak current system. For example, the working voltage of some cameras is 220VAC, so we cannot classify them as strong current systems.
The weak current system is mainly aimed at buildings, including buildings, residential areas, airports, docks, railways, expressways, etc.
Common weak current systems include: CCTV monitoring system, anti-theft alarm system, access control system, electronic patrol system, parking lot management system, video intercom system, home intelligent system and security system, background music system, LED display system, Plasma splicing screen system, DLP large screen system, three-meter copying system, building automation system, lightning protection and grounding system, paging intercom and professional intercom system, weak current pipeline system, UPS uninterruptible power supply system, computer room system, comprehensive Wiring system, computer LAN system, property management system, multi-functional conference room system, cable TV system, satellite TV system, satellite communication system, fire protection system, telephone communication system, hotel management system, video on demand system, human resource management system, etc.
Building weak current systems can generally be divided into three categories: communication automation system (CA——Communication Automation System), office automation system (OA——Office Automation System), building automation system (BA——Building Automation System), collectively referred to as 3A system. However, because there are many special regulations on the industry management of the fire automation system (FA——Fire Automation System) and the security automation system (SA——Security Automation System), sometimes the FA and SA systems are separated from the BA system, and the Building weak current systems are divided into five categories: CA, OA, BA, FA, and SA, collectively referred to as 5A systems. In fact, no matter how the entire system is divided, when it comes to engineering design and integration issues, it is still necessary to be specific to each subsystem.
2 System functions
Commonly used building weak current systems mainly include the following types:
(1) Telephone communication system. Realize the communication function of telephone (including three types of fax machines, video phones, etc.); star topology; use three types (or above) unshielded twisted pair, and the frequency of transmission signals is within the audio frequency range.
(2) Computer LAN system. It is the network basis for office automation and various data transmission; star topology; use five (or above) unshielded twisted pair wires to transmit digital signals, and the transmission rate can reach more than 100 Mb/s.
(3) Music/Broadcasting System. Play music through the speakers installed on the site (such as shopping malls, restaurants, guest rooms, corridors, etc.), and broadcast the site through the microphone; multi-channel bus structure; transmit constant voltage 120 V/120 Ω output from the power amplifier The audio signal is used to drive the sound of the live speaker, and the transmission line uses a copper core insulated wire.
(4) Cable TV signal distribution system. Evenly distribute the cable TV signal to each user point in the building; use branches and distributors for signal distribution, in order to reduce signal distortion and attenuation, and make the signal quality of each user point meet the requirements specified in the specification, the wiring is a tree structure, And it varies with the form of the building and the distribution of user points; use 75 Ω radio frequency coaxial cable to transmit multiple radio frequency signals.
(5) Security monitoring system. Through cameras, anti-theft detectors and other equipment installed on the site, monitor the entrances and exits of buildings and some important places and alarm for abnormal situations; the transmission of video signals adopts a star structure and uses video coaxial cables; the transmission of control signals The bus structure is adopted, and copper core insulated cables are used.
(6) Fire alarm system. The system consists of three parts: fire alarm and fire linkage system, fire broadcast system, and fire alarm intercom system.
The fire alarm and fire linkage system monitors the on-site conditions through fire detectors and manual alarm devices installed in various places in the building. equipment to control the spread of fire, and its signal transmission adopts a multi-channel bus structure, but for the transmission of linkage control signals of important fire-fighting equipment (such as fire pumps, sprinkler pumps, positive pressure fans, smoke exhaust fans, etc.), sometimes star-shaped Structure, signal transmission using copper core insulated cables (some products require the use of twisted pairs).
The fire broadcasting system is used to command the on-site personnel to evacuate safely in the event of a fire. It adopts a multi-channel bus structure, and copper core insulated wires are used for signal transmission (this system can be used together with the music/broadcasting system).
The fire alarm intercom system is used to command the on-site firefighters to carry out fire extinguishing work. It adopts star and bus structures, and shielded wires are used for signal transmission.
(7) Access control system. Use computers, smart card door locks, card readers and other equipment to set, monitor, control and record the status of each entrance and exit, so as to realize the unified management of each entrance and exit of the building and ensure the safety of the building. The topology and transmission medium vary from product to product .
(8) Parking lot fee management system. Through the induction coil installed under the ground of the entrance and exit, the entry and exit of vehicles are sensed, and the manual/semi-automatic/full-automatic toll management system is used to realize charging and control the opening and closing of electric railings. The wiring of this system is limited to the entrance and exit of the parking lot of the building. Each entrance and exit is controlled by a controller. The controller can work independently or be networked with the upper management computer. The wiring structure and transmission medium vary from product to product.
(9) Building automation system. Through various detection and execution devices connected to the on-site controller, various environmental parameters inside and outside the building and the working status of various equipment in the building (such as air conditioning, water supply and drainage, lighting, power supply and distribution, elevators, etc.) are detected. , monitoring and control, and connect the on-site controllers through the computer network to rationally allocate and manage the resources and equipment in the building to achieve the goals of comfort, convenience, economy and reliability. So far, there is no international standard for building automation systems, and the communication protocols used by different manufacturers’ products are different, and the topological structures and transmission media of the field bus and control bus are also different. The following will briefly introduce the LonWorks technology and BACnet technology that are generally accepted and adopted by the international community.
In addition, there are video conferencing systems, sound reinforcement systems, patrol systems, building intercom systems, and three-meter (water, electricity, and gas) automatic meter reading systems, etc. Buildings with different functions require different weak current systems.
3 System Integration
In actual work, designers should consider the integration of weak current systems from three aspects: network integration, function integration, and software interface integration.
3.1 Network Integration
Network integration is mainly considered from the wiring of each system, so that weak current systems with different functions can work on a unified wiring platform. Greater flexibility in layout.
In the commonly used building weak current system, the telephone communication system and the computer LAN system have different functions and hardware devices, but their network topology and information point layout principles are the same, and the same transmission media and connectors can be used. Therefore, the wiring of the two systems can be integrated into one wiring system. In this way, the two systems can be used for each other, and the functions of the information points can be interchanged, so that both systems have greater flexibility, which is what we call the integrated wiring system (PDS). For the remaining systems, considering the technical and economic feasibility, the current products cannot be integrated into the PDS due to the limitation of the system topology, signal transmission medium and twisted pair transmission power signal, etc. come. However, with the continuous development of digital signal processing theory and application technology, computer technology, communication technology, etc., the future PDS will definitely develop into a wiring platform that includes more weak current systems with different functions.
3.2 Function Integration
Functional integration includes the following two aspects:
(1) Merging functions. The main consideration is to merge some systems that are duplicated in function and hardware equipment, so that the merged system has all the functions of the systems before the merger, so as to reduce equipment redundancy and avoid duplication of investment. Among the above systems, the music/broadcasting system and the fire alarm and fire broadcasting system in the linkage system can be designed as a system, but the system must meet the “Code for Design of Automatic Fire Alarm System” (GBJ 50116-98).
(2) Complementary functions. From a functional point of view, each subsystem in the building automation system has its specific functions and jurisdiction, and usually works independently, but when some special events occur, it is often necessary for the systems to work together to improve the overall system. The ability of the system to deal with emergencies can realize overall control and management, and improve the intelligence of buildings. The specific linkage response includes the following systems:
Fire alarm system → music/broadcasting system: When a fire alarm occurs, the public address system on the corresponding floor will be forcibly switched to the fire emergency broadcast;
Fire alarm system → security monitoring system: When a fire alarm occurs, the security monitoring system will automatically cut the video images of the cameras in the area near the fire to the main monitoring screen of the security center, and focus on recording the video content of these cameras to confirm whether there is a fire alarm Occurrence and subsequent analysis of accident causes, etc.;
Fire alarm system → entrance and exit control system: when a fire alarm is confirmed, all control doors related to fire alarm parts in the entrance and exit control system (the control doors of important core parts can be set separately) should be automatically opened to facilitate internal personnel evacuation and withdrawal. entry of firefighters;
Fire alarm system→Garage management system: When it is confirmed that the fire alarm occurs on the ground floor or underground floor, the garage management system should open the garage control gate so that the vehicles in the garage can quickly evacuate from the fire scene (at this time, the relevant cameras in the garage should be in working and recording status);
Fire alarm system→Voice communication system: After the fire alarm system automatically confirms the occurrence of a fire alarm, it immediately sends an alarm to the fire station through the voice communication system in the building and transmits relevant information, and at the same time reports to the competent department of the building;
Building automatic control system → security monitoring system: When the building automatic control system has abnormal alarms or accidents, the security monitoring system can automatically cut the video images of the cameras in the area near the alarm to the main monitoring screen of the security center, and focus on monitoring and recording the video content of these cameras , for subsequent analysis of the cause of the accident, etc.;
Security monitoring system → building automatic control system: When the security system alarms, it can be linked with the elevator control system so that the elevator does not stop at the alarm floor, or stops at the floor designated by the security guard;
Access control system → security monitoring system: When the control door is not working when someone enters with a card or illegal intrusion occurs, the security monitoring system automatically cuts the video of the camera in the area near the entering control door or alarm point to the main monitoring of the security center screen, and focus on monitoring and recording the content of these cameras for verification when necessary;
Garage management system → security monitoring system: when there are vehicles entering and leaving the garage, the security monitoring system will automatically cut the video images of the cameras on the garage door to the main monitoring screen of the security center, and focus on recording the content of these cameras for verification when necessary .
In fact, there is no unified or fixed mode for the functional integration and linkage response among various systems, which can be set according to actual needs.
Functional integration is just the purpose. In fact, there are two modes. One is to build a higher-level management and control network on top of each subsystem, and the other is an integration mode centered on the building automation system. No matter which integration mode you choose, the key technology is to solve the communication problem between systems. When determining the solution, you must use a communication protocol with advanced theory, mature technology, and generally accepted and adopted by the industry.
A communication protocol in the field of building automation that is generally accepted by the international community is formulated by the American Society of Heating, Refrigerating and Air-Conditioning Engineers and has become the American National Standard BACnet standard ANSI/ASHRAE Standard 135—1995), which complies with ISO ( The OSI (Open System Interconnection) seven-layer model of the International Organization for Standardization contains five mature network communication protocols, including communication protocols such as Ethernet and LonTalk. Among them, the Ethernet communication protocol is a communication protocol commonly used in OA systems, and most network operating systems support this communication protocol; while LonWorks technology is a new generation of fieldbus technology developed by Echelon Corporation in the United States. Its outstanding advantage is that it supports Arbitrary topology, supports multiple transmission media (including twisted pair, power line, radio wave, infrared, coaxial cable and optical fiber), and multiple media can be mixed in the same network, thus greatly simplifying engineering construction and system completion renovation, expansion and maintenance work. Therefore, the building automation system conforming to the BACnet standard can be easily integrated with the OA system at the control bus level, and because its inclusive communication protocol supports twisted pair and star topology, it can use PDS as its signal transmission way.
3.3 Software interface integration
When realizing the functional integration of each system, the integration mode is selected, the network communication protocol is determined, and the corresponding hardware devices are physically connected to each system, and an interoperable network operating system is installed. The final work is to develop a corresponding application software connects each system logically and provides a unified man-machine interface for the whole integrated system, which is software interface integration.
In short, system integration is a highly technical system engineering. To truly integrate a weak current system in a building, it not only requires weak current engineers to have in-depth knowledge of the functions, technical parameters, construction, installation, and commissioning of each weak current system product. To master, it is necessary to have a relatively comprehensive understanding of the building’s water supply and drainage system, power supply and distribution system, ventilation and air conditioning system, lighting system, elevator system, etc. It is a modern high-tech with high technical content and very fast update development. Therefore, in the specific implementation process of system integration, the support and cooperation of professional and technical personnel from all aspects are needed to solve many technical details.
Weak current engineering Intelligent building electrical technology still includes two types: strong current and weak current. The electricity consumption of buildings and buildings generally refers to the strong electricity of 220V50Hz and above. It mainly provides electric energy to people, such as electricity for electric drive motors, electricity for lighting and so on. There are two main types of weak electricity in intelligent buildings. One is low-voltage electric energy such as the safety voltage level and control voltage stipulated by the state, which can be divided into AC and DC, such as 24V DC control power supply, or emergency lighting backup power supply. The other type is information sources that carry information such as voice, images, and data, such as information from telephones, televisions, and computers.
People are used to referring to weak current technology as weak current technology. It can be seen that the basic meaning of weak current technology for intelligent buildings is still weak current technology in the original sense. However, with the rapid development of modern weak current high-tech, the application of weak current technology in intelligent buildings is becoming more and more extensive. The degree of application of weak current technology determines the degree of intelligence of intelligent buildings.
The voltage below 36v is called safe voltage, that is, weak current.
There are two main types of weak electricity in buildings:
The intelligent system is a building equipment monitoring system, safety protection system, communication network system, information network system, automatic fire alarm and fire linkage system, and is a comprehensive system for the purpose of centralized monitoring, control and management;
All kinds of data collection, control, management and communication control or network system lines in the home are called intelligent lines (that is, weak currents in home decoration).
