Weak current system is mainly divided into the following categories:
1. Telephone communication system
Realize the communication function of telephone (including three types of fax machines, videophones, etc.); Star topology; Class III (or above) unshielded twisted pair cable is used, and the transmission signal frequency is within the audio range.
2. Computer LAN system
It is the network foundation to realize office automation and various data transmission; Star topology; Class 5 (or above) unshielded twisted pair cable is used to transmit digital signals at a transmission rate of more than 100 Mb/s.
3. Music/radio system
Play music through loudspeakers installed on the site (such as shopping malls, restaurants, guest rooms, corridors, etc.), and broadcast on the site through microphones; Multiplex bus structure; Transmit the constant voltage 120 V/120 Ω audio signal output by the power amplifier to drive the field speaker to sound. The transmission line uses copper core insulated wire.
4. CATV signal distribution system
Distribute cable TV signals evenly to all user points in the building; Branches and distributors are used 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, its wiring is tree structure and varies with the form of buildings and the distribution of user points; Use 75 Ω RF coaxial cable to transmit multiple RF signals.
5、 monitoring system
By installing video camera , anti-theft detectors and other equipment to monitor the entrances and exits of buildings and some important places and alarm for abnormal conditions; The transmission of video signal adopts star structure and video coaxial cable; Bus structure is adopted for transmission of control signal, and copper core insulated cable is used.
6. Fire alarm system
The system consists of fire alarm and fire linkage system, fire broadcast system, fire alarm intercom telephone system and other three parts.
The fire alarm and fire fighting linkage system monitors the site conditions through the fire detectors and manual alarm devices set in various parts of the building. When there is an alarm signal, the system will link the corresponding equipment according to the received signal and the preset procedure to control the spread of the fire. The signal transmission adopts the multi-channel bus structure, However, for the transmission of linkage control signals of important fire-fighting equipment (such as fire pump, spray pump, positive pressure fan, smoke exhaust fan, etc.), sometimes the star structure is used, and copper core insulated cables are used for signal transmission (some products require twisted pair cables).
The fire broadcast system is used to command the safe evacuation of on-site personnel in case of fire. It adopts a multi-channel bus structure, and uses copper core insulated conductors for signal transmission (the system can be shared with the music/broadcast system).
The fire alarm intercom telephone system is used to command the on-site firefighters to carry out fire fighting work. It adopts two structures: star type and bus type. Shielded wire is used for signal transmission.
7. Access control system
Use computers, smart card locks, card readers and other devices to set, monitor, control and record the status of each entrance and exit, so as to achieve unified management of each entrance and exit of the building and ensure the safety of the building. Its topology and transmission media vary from product to product.
8. Parking charge management system
The induction coil installed under the ground at the entrance and exit is used to sense the entrance and exit of vehicles, and the manual/semi-automatic/full-automatic toll management system is used to realize toll collection and control the opening and closing of electric railings. The system wiring is only limited to the entrance and exit of the building parking lot, and each entrance and exit is provided with one controller Control, the controller can work independently, and can also be networked with the upper management computer. Its wiring structure and transmission media vary from product to product.
9. Building automation system
Detect, monitor and control 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.) through various detection and execution devices connected to the field controller, and connect the field controllers through the computer network to reasonably allocate and manage the resources and equipment in the building, It is comfortable, convenient, economical and reliable. Up to now, there is no international standard for building automation system. The communication protocol adopted by different manufacturers is different, and the topology and transmission medium of field bus and control bus are also different.
In addition, there are video conference system, sound reinforcement system, patrol system Building intercom Automatic meter reading system, etc. Buildings with different functions need different weak current systems.
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