Design of distributed intelligent fire alarm control system

    Abstract: The design method of a distributed intelligent fire alarm control system, the composition and implementation of system software and hardware are given. The system design adopts multi-CPU parallel processing and intelligent data processing methods to achieve real-time, accurate alarm and reliable linkage control of the system, and uses field bus CAN to realize controller networking. Practice shows that the system has high reliability, strong flexibility and friendly human-machine interface.

    Keywords: Intelligent fire alarm microcontroller network CAN bus 

    The intelligent fire alarm control system is a control system that integrates signal detection, transmission, processing and control, and represents the development direction of today's fire alarm systems. With the rapid development of science and technology and the rapid growth of domestic and foreign economies, the market is in urgent need of an intelligent fire alarm control system with large capacity, superior performance, high reliability, and easy installation, use and maintenance.

    This article gives the design, composition, implementation methods and characteristics of an intelligent fire alarm control system designed by the author that has the international advanced level in the 1990s. The system adopts advanced computer technology and communication technology, and has intelligent features such as programmability, automatic adjustment of fire alarm sensitivity and automatic drift compensation. It works more stably and reliably and has a wide range of applications.

    1 System network structure

    In order to achieve large-scale and large-scale fire monitoring, fast and reliable communication between controllers and between controllers and repeaters must be achieved. CAN (Controller area Network) bus is a serial data communication bus developed by the German Bosch company in the early 1980s to solve the problem of data exchange between numerous control and test instruments in modern automobiles. Since the CAN bus emphasizes real-time, It also has extremely high reliability and unique design, and is particularly suitable for the interconnection of industrial process monitoring equipment. Therefore, it has attracted more and more attention from the industry and has been widely used. It has a very broad development prospect. Its maximum communication rate can reach 1Mbps and the communication distance can reach 10km. Since the communication distance between controllers is long, the transmission of information is large and the real-time and reliability requirements are high, it is very appropriate to choose CAN bus to realize communication between controllers. Due to the short communication distance and less information transmission between the controller and the repeater, the RS-485 bus is used for networking. The system network structure is shown in Figure 1.

    2 Controller hardware design

    System hardware design should first meet the basic fire alarm functions and various reliability and anti-interference requirements in national standards. Secondly, it provides a flexible configuration so that it can be suitable for various applications. At the same time, the system should be scalable, making it easy to expand and upgrade the system during the development process.

    2.1 Adopt multi-CPU working mode and modular structure

    The adoption of multi-CPU working mode is mainly to solve problems such as real-time performance and multi-task deployment. The controller not only collects the parameters and status of various detectors and modules in real time, but also performs many tasks such as data processing, LCD display, printing, communication and control. A single microcontroller cannot complete the above work in real time. It is necessary to adopt multi-CPU working mode and modular structure. Passed between CPUsC bus for communication. The block diagram of the controller is shown in Figure 2.

    2.2 Main CPU module design

    The main CPU module is used to monitor and control various functional components, perform various data processing, network communication and data storage, etc. It is the core of the entire controller. It is designed with the microcontroller 80C652 as the core and consists of program memory, data memory, monitoring and self-test circuits, I/O interfaces and communication interfaces, as shown in Figure 3. The communication interface is CAN bus, RS-485 and RS-232C. CAN is used for networking between controllers, RS-485 is used for networking between controllers and repeaters, and RS-232 can be directly connected to PC. machine, printer or modem.

    2.3 Loop scanning CPU module design

    The loop scanning CPU module realizes the addressing of various detectors and control units, and collects the information returned by each address unit, including smoke concentration analog quantity, ambient temperature analog quantity and various status information reflecting peripheral components, and analyzes this information Analysis and processing are performed, and the results are transmitted to the main CPU via the loop bus. According to the implemented functions, it mainly consists of seven parts: peripheral component drive circuit, voltage detection circuit, interference suppression circuit, overcurrent protection circuit, loop CPU and main CPU interface circuit. The relationship between them is shown in Figure 4.

    3 CAN bus interface design

    This system is a controller local network composed of many intelligent fire alarm controllers connected through the CAN bus. Therefore, the design of the CAN bus is extremely important. Among them, the selection of CAN controller, CAN driver and anti-interference measures will become the key to the design.

    3.1 Selection of CAN controller

    For further expansion of the system, SJW1000 that supports CAN2.0B communication protocol can be selected. SJW1000 is the latest CAN controller produced by PHILIPS that supports both CAN2.0B and CAN2.0A. It is fully compatible in hardware and software with the CAN controller 82C200 that only supports CAN2.0A.

    3.2 CAN interface chip 82C250

    82C250 is the interface between PHILIPS' CAN controller and the physical bus, providing differential sending and receiving capabilities for the bus. It is fully compatible with the ISO/DIS 11898 standard and has three different working modes, namely high speed, slope control and standby, which can be selected according to the actual situation.

    3.3 Photoelectric isolation

    In order to further improve the anti-interference ability of the system, a photoelectric isolation circuit is added between the SJW1000 and the driver, and a DC-DC converter is used as the power supply, as shown in Figure 5.

    4 System features

· The system uses advanced analog sensors, microcontrollers and intelligent algorithms, which can automatically compensate for drift caused by various non-fire factors and automatically detect the performance of the detector. It can effectively prevent false alarms and missed alarms caused by various factors and achieve accurate alarms.

· A control matrix is ​​designed in the system, and software programming can be used to realize automatic fire protection linkage, replacing traditional hardware combination logic. It not only facilitates design and construction, but also greatly improves the flexibility and scalability of fire protection linkage.

· The system has rich self-diagnosis functions, which can promptly detect system faults and their locations, reduce maintenance time, and create conditions for the normal operation of the equipment.

· The system adopts a distributed modular structure to form a microcomputer local area network, which can be flexibly configured according to needs and has a wide range of applications.

· The system adopts multimedia technology and has Chinese character input, display, voice and sound and light alarm functions, and the human-machine interface is very friendly.

    The system uses a distributed modular structure to form a communication network, with flexible configuration and strong adaptability; it adopts multi-CPU collaborative working mode, which effectively solves the contradiction between real-time and multi-tasking; data processing uses linear and non-linear filtering, threshold detection and Intelligent algorithms such as process analysis lay the foundation for accurate alarms; the system uses fault self-diagnosis technology and multimedia technology.