Design and implementation of automatic fire alarm control system based on CANBUS

The automatic fire alarm control system is an automatic fire alarm system that assists people in early detection and notification of fires, and can take effective measures to extinguish fires in the smoldering stage of flames. It is an indispensable safety technical facility for fire protection in various industries and civil buildings. Therefore, the reliability of system operation is very important. Once false alarms or failure to report occur, it will cause great losses to people's lives and property. With the continuous development of communication technology, the original serial communication technology can no longer meet the requirements of the communication interface of large-scale fire automatic control systems. It is imperative to design and transform the communication interface of the automatic fire alarm control system using CANBUS fieldbus technology.

1 System Design and Implementation

In the design process of fire automatic alarm control system, centralized control system is generally adopted. In the partition fire extinguishing control, hundreds of fire alarm controllers are often required to be connected. If the system connection distance between the main controller and the partition fire extinguishing controller exceeds the distance that the serial port RS485 communication can bear, communication interruption, data transmission error and other problems will occur. In the past, RS485 communication was applied to fire automatic alarm control systems with a communication distance of no more than 1 000 M. Once this upper limit is exceeded, it cannot work normally. The characteristics of RS485 communication are: 1) There can only be one master node on the master-slave structure network, and the rest are slave nodes. It is impossible to form a multi-master structure or redundant structure system. Therefore, the reliability of the master node is required to be high. Otherwise, once the master node fails, the entire system will be paralyzed; 2) Since the RS485 data communication method is command response type, the slave node cannot actively send data, which reduces the data transmission efficiency on the network and makes the master node controller very busy. At the same time, when an abnormality occurs at the lower end, the data cannot be uploaded immediately and must wait for the command of the master node.

After analyzing the characteristics of RS485 serial port communication, CANBUS communication with no master-slave distinction and multi-master working mode is used to realize the communication interface function of the fire automatic alarm control system (as shown in Figure 1 below). It completely solves the problems that the RS485 serial communication used in fire protection products has long been bothering people, such as the inability of slave nodes to actively exchange data with other nodes, short communication distance, and small number of nodes. CANBUS technology is used to solve the centralized management requirements and long-distance communication reliability in fire protection products. The CANBUS bus communication mode is a two-wire system, which can facilitate the wiring of the system and reduce electromagnetic interference between signals. Since the number of CANBUS network nodes can reach as many as 110, the fire control center can expand the number of points of the fire automatic alarm controller, which is suitable for large and medium-sized fire alarm systems. Since the CANBUS network technology adopts a short frame structure, each frame has 8 valid bytes, so the transmission time is short, the probability of interference is low, and it has a good detection effect.

2 System Hardware Design

The hardware circuit design of the CANBUS communication port in the automatic fire alarm control system is shown in Figure 2.

In large and medium-sized fire alarm control system networks, fire signals of several buildings are monitored and managed. Each building is equipped with fire alarm control and bus input devices (temperature detectors, smoke detectors, photoelectric detectors, manual fire alarm buttons, bus input modules, bus output modules, bus master modules, fire hydrant buttons, etc.). The communication within a fire alarm control system adopts RS485 serial communication, while the communication between fire alarm control systems adopts CANBUS bus technology, which greatly improves the reliability of communication in the entire network. In the entire system, the fire detector mainly detects the air content of the protected space, and uses microprocessor technology to analyze and process the data detected by the sensor. It can keenly detect the smoke generated by the initial smoldering stage of the fire within the protection range. Once the threshold is reached, an alarm signal is sent to the fire alarm controller. The fire alarm controller judges and identifies the polarity of this signal, confirms the fire signal after continuous detection for 3 times, and sends the linkage information to the linkage control system through the CANBUS communication interface according to a certain logical relationship, and starts the corresponding linkage equipment for effective fire extinguishing.

The SJA1000 in Figure 3 is a CANBUS controller, which is specially used to manage CANBUS communication. SJA1000 is a replacement for Philips' early CAN controller PCA82C200. It has more powerful functions than CA82C200, which is mainly reflected in the following aspects: 1) Fully compatible with PCA82C200 and its working mode; 2) With an extended receive buffer and 64-byte FIFO structure; 3) Support CAN2.0B; 4) Support 11-bit and 29-bit identification codes; 5) The bit rate can reach 1 Mbit/s; 6) Support peliCAN mode and its extended functions; 7) 24 MHz clock frequency; 8) Support interface with different microprocessors; 9) Programmable CAN output driver configuration; 10) Enhanced temperature range of -40 to +125℃. 82C250 is used to prevent crosstalk between lines. If necessary, optocouplers should be used for current isolation, which will have a better effect.

3 System software design

The main function of the system software design is the communication between the fire alarm controller and the fire center. The fire alarm controller transmits the fire signal to the fire center through CANBUS. After receiving the signal, the fire center starts the corresponding linkage equipment and display equipment. CAN receiving and sending data are generally implemented in the CAN interrupt program, and the data length of each frame is ≤8 bytes. If there is an error in sending or receiving, CANBUS has error detection capabilities, and errors occurring in all nodes can be detected 100%. SJA1000 has all the necessary features required to complete high-performance communication protocols. SJA1000 with simple connections can complete all functions of the physical layer and data link layer.

The flow chart of CANBUS receiving interrupt service program is shown in Figure 3.

Cx51 language programming is as follows:

From the above program design, we can see that the data sending and receiving of CANBUS field bus technology are completed in the interrupt service program. If data is to be sent, first determine the length of the data. If it is an integer multiple of 8, then use the full frame sending method, otherwise use the non-full frame sending method.

4 Conclusion

After applying CANBUS bus communication technology to the automatic fire alarm system, the problems of communication distance, node capacity and expansion are solved, and the application of the automatic fire alarm system is expanded from one building to several building groups, forming a large fire alarm network. In this network, the transmission of information is reliable, fast and convenient, and the two-wire communication method facilitates the wiring of the system and reduces interference between signals. At the same time, the alarm systems between networks do not interfere with each other.