Basic information about automatic fire alarm system

10/04/2023

Today PCC Southeast will bring you basic information about automatic fire alarm system please follow the article.

1. OVERVIEW OF DUTIES OF AUTOMATIC FIRE ALARM SYSTEM

1.1. General

Automatic fire alarm system lis a system of automatic detection and notification of fire locations (according to Vietnamese standards TCVN 5738-2001). Automatic fire alarm system includes: Fire alarm center, fire detectors, (combination of bells, lights, push buttons) and other peripheral devices...

1.2. Mission

Automatically detect fire quickly, accurately and promptly in the area

system is protected.

Automatically emit alarm signals, instructions and control signals for peripheral devices of automatic fire alarm systems to perform a specific task.

In particular, with an automatic fire alarm system using a smoke detector, it has an even more important task of "alarming", ie detecting and notifying the impending fire, the smoldering fire without flame. .

1.3. Classification of automatic fire alarm system

Classification of automatic fire alarm systems according to the working principle of fire detectors has:

- Automatic fire alarm system using smoke detector: is an automatic fire alarm system that works based on the working principle of smoke detectors. This system mainly detects the increase in smoke concentration in the protected area.

- Automatic fire alarm system using heat detector: is an automatic fire alarm system working on the working principle of a heat detector. This system mainly detects the temperature change in the protected area.

- Automatic fire alarm system using light (fire) detectors:  Works based on the working principle of fire detectors. This system mainly detects the light-enhanced concentration of the flame in the protected area.

- Automatic fire alarm system using mixed fire detectors:  is a working system based on the working principle of mixed fire detectors such as heat and smoke detectors; heat and fire detectors. This system mainly detects the change of environmental factors in the protected area.

Classification of automatic fire alarm systems according to the specification of the fire alarm system.

- Automatic fire alarm system by zone (normal automatic fire alarm system) :  (common automatic fire alarm system - Couventional fire alarm system): is an automatic fire alarm system that has the function of alerting a fire to an area. area, a location  (may have one or more fire detectors). The protected area of an area can be from a few tens to 2000 m2  (depending on the characteristics of that area).

- Addressable fire alarm system: (Addressable fire alarm system) : is an automatic fire alarm system capable of accurately reporting fire to each location of each separate detector (for each specific address). The protection area of a fire alarm address is limited to a few tens of square meters  (depending on the type of fire detector). Intelligent automatic fire alarm system: With the development of science and technology, the address-based automatic fire alarm system has developed into an intelligent fire alarm system (Intelligent fire alarm system). This is an automatic fire alarm system in addition to the conventional fire alarm function according to the address, it can also measure some environmental parameters of the area where the fire detector is installed such as temperature, smoke concentration, etc. and can change the impact threshold of the fire detector according to the requirements of the designer and installer. In practice, this classification is often used.

2. WORKING PRINCIPLES OF AUTOMATIC FIRE ALARM SYSTEM

2.1. Working states of automatic fire alarm system

+ Permanent state (when there is no fire)

+ State of fire alarm

+ Crash status

2.2. Working Principle

+ Normally the whole system is in standby mode. In this mode, the fire alarm center always has a signal to check the work of the equipment in the system and the addressable fire detectors, modules, etc. also have a response signal to the center. Periodically, from time to time (depending on setting) the center will print the status of the system and information about the equipment that needs maintenance. In the circuit there is always current Io flowing through.

+ In monitoring mode, if the center receives an error signal from the devices or does not receive a response signal from the devices, the center will switch to trouble mode. All fault information will be displayed on the LCD liquid crystal display. Once the fault is rectified, the crash mode will end and return the system to normal monitoring mode.

+ When fire occurs in protected areas, changes in fire environment factors (temperature, smoke, light) will affect the fire detectors. When these factors reach the working threshold, the fire detectors will work to generate a signal transmitted to the center (including the fire alarm signal and the address signal of the fire alarm device). At the fire alarm center, signal processing activities will take place according to the installed program to give a signal to notify the area of fire through the central speaker and LCD liquid crystal display. At the same time, the corresponding peripheral devices will activate to emit fire alarm signals and perform the set tasks.

+ In case the fire alarm center is installed with the function of monitoring other equipment, when there is a change in the status of the equipment (for example, the fire pump works, the flow switch works... ), the system will switch to notifying the device to be monitored for a state change. Information about this change will be displayed on the center's lap crystal display. This mode will also terminate automatically if the devices to be monitored return to their normal position.

2.3. Technical requirements for automatic fire alarm system

According to Vietnamese standard TCVN 5738 - 2001 "Automatic fire alarm system - Design requirements", it is stipulated that the power report system must meet the following requirements:

+ Detect fire quickly according to the proposed function.

+ Convert the fire signal into a clear alarm signal so that people around can immediately take appropriate measures.

+ Has good anti-interference ability (interference usually occurs when the signal conductor is located in the area with strong electric field or when the conductor is placed next to the wire). Thus, to prevent interference, an anti-interference signal can be used or a normal signal wire, but must be placed in a metal tube.

+ Quickly and clearly signal all system problems.

+ No partial or complete paralysis caused by fire before detecting fire.

+ The system must operate continuously in all conditions (AC, DC power)

+ The installation of fire detectors with the fire alarm center must pay attention to the suitability of the system (Voltage supplied to the fire detector, type of fire alarm signal, method of incident detection...).

+ The fire alarm system must ensure reliability. The system must fulfill the intended functions without errors.

+ External influences that cause failure to a part of the system must not cause further problems in the system.

+ Automatic fire alarm system in addition to meeting the above requirements, the parts of the system also need to meet its own requirements in accordance with the set standards.

3. FIRE Detector

3.1. Concept - duty of fire detectors

3.2. Concept

A fire detector is a sensor device that is sensitive to changes in environmental factors when burning such as temperature, light, smoke concentration, to generate signals transmitted to the center when the values of these factors are detected. environment reaches a certain value (threshold).

3.3. Tasks of fire detectors

The fire detector has the task: to generate an electrical signal to transmit to the center when the elements of the environment around the detector reach a certain value. The fire detector can be considered as a communication device between the environmental factors of the fire and the automatic fire alarm system.

The fire detector can only perform its task when the environmental factors of the fire in its protected area reach the working threshold.

The electrical signal that the detector generates is mainly in two main forms:

- Signal to open or close the contact.

- The signal changes suddenly in the value of the current.

Depending on the type of fire detector, the electrical signal it generates is different.

4. CLASSIFICATION OF FIRE Detectors

​4.1. According to the working principle of the fire detector :divided into 4 categories:

- Heat detector: Works based on the variation of the temperature element.

- Smoke detector: Works based on the change of smoke concentration.

- Fire detector: Sensitive to light (flame).

- Mixed fire detector: Works based on the transformation of 2 of the 3 factors above.

4.2. Classification according to power supply condition: divided into 2 types:

- Active fire detector: No need to power the detector, it still works.

- Passive fire detectors: Constantly having to supply power to the detector.

4.3. Classification by specification

-Conventional fire detectors: Usually used for regional fire alarm systems.

- Addressable fire detectors: Usually used for addressable fire alarm systems.

4.4. Sort by operating mode

- Maximum fire detector.

- Differential fire detector.

- Maximum fire detector - differential.

5. STRUCTURE OF WORKING PRINCIPLES OF FIRE Detectors

5.1. Structure:

Depending on each type of fire detector, on the working principle, the fire detectors have different structures. But in general, the fire detector consists of the following parts:

+ Sensor: This is the most important part of the fire detector. It senses the change of environmental factors and converts that change into an electrical signal when these factors reach an appropriate preset value. With each different type of fire detector, the sensor part is different.

+ Signal circuit part: is an electronic circuit that is responsible for transmitting signals from the sensor part to the transmission device.

+ Shell - base: is the part that protects and fixes the fire detector in the area to be protected.

5.2. General principle:When a fire occurs, environmental factors will be changed. These factors will affect the fire detector and the working fire detector to generate electrical signals transmitted to the center.

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