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Introduction to weak basic knowledge

View:101305/27/2017  

Recently, there are some friends who want us to send some basic knowledge of weak electricity, these days also time to tidy up, I hope useful for some friends.

Weak current generally refers to the DC circuit or audio, video lines, network lines, telephone lines, DC voltage is generally less than 32V. Telephone, computer, TV signal input (cable TV line), audio equipment (output terminal line) and other appliances are all weak electrical equipment in household appliances.

Building weak current

In the construction of weak mainly have two kinds: one is the national security requirements of the voltage level and control voltage of low voltage power, with AC and DC points, such as the 24V DC power supply, emergency lighting or standby power supply.

The other is the information source, such as telephone, TV and computer, which contains information such as voice, image, data and so on.

narrow sense

In narrow sense, building weak current mainly refers to: Security (surveillance, perimeter alarm, parking), fire (Electrical), building control, network cabling and audio systems.

Intelligent system for construction equipment monitoring system, security system, network communication system, information network system, automatic fire alarm and fire linkage system, integrated system of the centralized monitoring, control and management; all kinds of data acquisition, control, management and communication within the family control network system or other lines, then called the intelligent line (also known as home decoration in the weak).

Difference with strong electricity

Strong and weak currents are conceptually easy to distinguish, and the main difference is the difference in uses. Strong electricity is used as a power source, and weak electricity is used for information transmission. They are roughly the same as the following:

AC frequency is different

The frequency of strong electricity is generally 50Hz (Hz), called "power frequency", which means the frequency of industrial power: the frequency of weak current is often high frequency or ultra high frequency, with KHz (kHz) and MHz (MHz) meter.

Different transmission mode

Strong current is transmitted by power line, and weak current is divided into cable and wireless. The radio is transmitted by electromagnetic wave.

Power, voltage and current vary in size

Electric power KW (kw) and MW (MW) meter, voltage to V (V), KV (kV), current to A (an), kA (KA); weak power to W (Watts), mW (MW), voltage to V (V), mV (MV), current to mA (MA), uA (a), so the circuit can be formed by printed circuit or integrated circuit.

Strong current also has high frequency (hundreds of KHz) and intermediate frequency equipment, but the voltage is higher and the current is larger. Due to the development of modern technology, the weak current has penetrated into the field of high voltage, such as power electronics devices, wireless remote control, etc., but these can only be counted as the weak part of the strong current, and it is still different from the charged strong current.

Weak current system

The weak current system of intelligent building is the basic member of intelligent group in intelligent building. It is also the key component of intelligent building, and is the main object of daily work for building electrical professionals. Prior to 70s, the design of the weak only telephone and radio design, and after 80s, in its content increased fire alarm and linkage control, common antenna, security monitoring, air conditioning, DDC control. The design content of the weak current is expanding and expanding step by step, the technology is more and more new, the workload is more and more big, and the intelligent building weak current system generally includes the following subsystems:

Building automation management system (BAS), automatic fire alarm system (FAS), security monitoring system (CCTV), satellite and cable TV system (CATV), the underground garage management system (CPS), public broadcasting and emergency broadcast system (PAS), process control switch system (PABX), structured cabling system (PDS) etc.. In the building automation management subsystem, it often contains the entrance and exit control subsystem and anti-theft alarm subsystem.

Intelligent building various subsystems provide monitoring and management for various electrical and mechanical equipment for building, building for the user to create a safe, healthy, comfortable and pleasant and can improve the efficiency of the office environment, provides modern means of communication and office conditions, to meet the various requirements of users for different environment and function.

Building automation management system (BAS) building automation management system is the core of intelligent building weak electricity system, its high reliability is the cornerstone of the weak system of high reliability, so BAS system adopt three level control mode.

Automatic fire alarm system (FAS) adopts intelligent smoke sensing probe and a temperature sensing probe, intelligently sensing smoke and heat, the corresponding analog value is given, by using the advanced algorithm, enables the system to distinguish between true and false alarm interference. The system's display screen can graphically display the exact location of the fire and the nature of the alarm. After the fire alarm is confirmed, the system can automatically send out the corresponding fire emergency broadcast and fire control linkage, which lays the foundation for the safe evacuation of the personnel and the correct and effective fire extinguishing.

Security monitoring system (CCTV) by closed-circuit TV monitoring system, entrance control, patrol system and burglar alarm system.

Satellite reception and cable television subsystem, satellite receiver and cable TV subsystem (CATV) are the basic systems now in common use. The satellite receiving system is the use of satellite television signals to direct forwarding system, which is equivalent to a space relay station that is the best way to solve the problem of TV coverage and high quality transmission of TV image signal.

The cable television (public antenna) system uses a set of high-quality antennas to distribute television signals to each use of the television system in wired mode


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