Fire Remote Monitoring System Based on CAN Bus

0 Introduction:
Fire remote network monitoring technology developed on the basis of modern communication and network transmission technology can ensure the normal operation of fire detection alarm system and fire safety facilities and play its due role. This paper introduces the use of CAN bus in distributed control and data transmission to achieve distributed remote fire information data collection; then use embedded gateway to achieve seamless connection from CAN to Ethernet LAN or Internet, which improves the transmission distance of fire information, thereby utilizing existing network resources to achieve remote monitoring of fire information.
1. System overall framework design
The data acquisition terminal in the fire remote monitoring system is a variety of fire signal detectors located at the collection site, and scattered in different locations (floors), while the centralized alarm controller is in the central control room (fire control room). The distance between them is usually between tens of meters and hundreds of meters, and sometimes even reaches several thousand meters. Therefore, it is particularly important to have fewer connecting wires, high reliability, good real-time performance, strong anti-interference ability, and high cost performance. In order to solve the above problems, CAN bus is used to solve the problems of distributed control and reliability, real-time performance, anti-interference ability, etc. At the same time, embedded gateway is used to solve the access problem of Ethernet and Internet [1], so that the fire can achieve the purpose of remote network monitoring of fire information. The overall structure of the system is shown in Figure 1.

This system is divided into three levels: (1) The bottom layer is a distributed data acquisition network based on the CAN bus, which is used to realize the collection of field data and the communication and data transmission between the bottom layers; (2) The middle layer is a gateway based on embedded technology. The embedded gateway with DS80C400 produced by MAXIM as the core realizes the seamless connection from CAN to Ethernet LAN and Internet. Through this gateway, the data collected from the bottom layer can be transmitted to the control computer or data server; (3) The top layer is the existing Ethernet LAN and Internet.
2 Fire signal acquisition network based on CAN bus (bottom layer design)
CAN bus is a serial communication network that effectively supports distributed control or real-time control. One of the biggest features of the CAN protocol is that it abolishes the traditional station address encoding and replaces it with encoding of communication data blocks. The advantage of using this method is that the number of nodes in the network is theoretically unlimited. The identification code of the data block can be composed of 11 or 29 binary numbers, so 211 or 229 different data blocks can be defined. This data block encoding method can also enable different nodes to receive the same data at the same time. The CAN bus uses a short frame structure to ensure real-time communication. The CAN protocol uses CRC check and can provide corresponding error handling functions to ensure the reliability of data communication [2]. These characteristics
of the CAN bus meet the functional requirements of the fire monitoring system. The underlying structure of the fire monitoring system based on the CAN bus is shown in Figure 2. In the system, the control center host is the upper computer. During operation, it is responsible for asking the centralized controllers on each floor for various fire detector data and working status, and judging and displaying the floors and specific locations where fires have occurred or may occur. The centralized controllers on each floor are composed of a CAN bus controller, a CAN transceiver, a detector communication interface, and a manual alarm device. The CAN bus controller is used for data transmission between the centralized controller and the control center host; the CAN transceiver enhances the driving capability of the controller and ensures the communication distance; the detector communication interface is connected to various detectors and manual alarm devices.
When sending data, the fire alarm writes the data to be transmitted into the sending buffer of the CAN controller, starts sending, and the data is sent to the bus through the CAN transceiver; when receiving data, the CAN controller receives data from the bus through the CAN transceiver, stores it in the receiving buffer after processing, and gives a receiving interrupt signal. At this time, the centralized controller can take data from the receiving buffer of the CAN controller.

Figure 2 The underlying structure of the fire remote monitoring system

The RS232/CAN converter is the interface between the host computer of the control center and the CAN bus, and converts the transmitted information between the RS232 bus standard and the CAN bus standard. In addition, the functions of message splicing and splitting, and sending time calibration commands to the centralized controller at regular intervals are also completed by the converter. The structure of the RS232/CAN converter is shown in Figure 3.

The embedded gateway is the core component of the system. It mainly completes the protocol conversion and data transmission from the field bus to Ethernet, and realizes the communication from the bottom data acquisition network to the upper monitoring and management network. The selection of the hardware platform of the gateway should fully consider the requirements of safety, economy, and development cycle. It is a good choice to use the DS80C400 dedicated chip and conduct secondary development on this basis. The dedicated chip is moderately priced and integrates a large number of on-chip devices for development, such as TCP/IP protocol stack, Ethernet controller, etc., which shortens the development cycle and development difficulty, has high reliability, and has a good cost performance. The embedded Ethernet gateway is mainly composed of the network microcontroller DS80C400 and the Ethernet interface chip LXT972ALC, as shown in Figure 3.

DS80C400 is a fast and highly integrated network microcontroller compatible with 8051. It executes instructions three times faster than ordinary 8051. Its peripherals include 10/100bps Ethernet, 3 serial ports, 1 CAN2.0B controller,
a 1Wire controller and 64 I/O pins, and a TCPIPv4/6 protocol stack. DS80C400 integrates a 10/100Mbps Ethernet controller and is a physical device that supports connection using the IEEE802.3 protocol.
LXT972ALC is a receiver and transmitter chip that complies with the Fast Ethernet protocol. LXT972ALC supports the standard MII of 10/100MMAC. LXT972ALC performs all the physical coding sublayer and physical attachment sublayer functions of the standard 10BASE-X defined by IEEE802.3 [4]. It can also perform all the functions of all the media independent sublayers of the 10BASE-TX connection.
4 Top-level data transmission requirements based on Ethernet and Internet [5]
The top-level of the fire remote monitoring system is the general Ethernet and Internet network. Its software and hardware structure is ready-made, but when it is used in the fire remote monitoring system, the real-time, reliability and security of the system data transmission must be considered [4].
4.1 Real-time requirements for data transmission
Early fire alarm is the most effective measure to extinguish the fire in time and reduce losses. The earlier the fire is discovered and the more timely the fire is extinguished, the less likely it is to cause a disaster. Otherwise, a small fire may cause a big disaster and cause incalculable losses. Therefore, the real-time requirements of the system are important.
However, since data transmission on the Internet is stored and forwarded in the form of data packets by establishing a virtual connection, there is a time delay. Routers are the core of the Internet network. According to the working principle of routers, routers generally forward IP packets based on the principle of fairness and first-come-first-served. There are two main factors that cause IP packet delay: one is the routing query time, and the other is the IP packet queuing time. In particular, when the network is blocked, it causes a large delay in IP and even discards IP packets when the queue is full, resulting in data loss in network transmission.
To solve the real-time problem of the remote fire monitoring system, the actual focus is to solve the transmission delay problem of fire information on the Internet. Internet network delay generally includes routing table delay, packaging delay, transmission delay, queuing delay and processing delay. Among them, routing table delay, propagation delay and queuing delay are the main factors affecting network delay.
4.1 Reliability requirements for data transmission
In the development of the Internet, the reliability of services has become an increasingly important issue. Due to the importance of the remote fire monitoring system, the loss of fire monitoring information data packets will cause immeasurable losses. Generally, the system requires high fault tolerance. Traditional reliability measurement indicators include: failure rate, mean failure time, failure interval time, mean repair time and fault coverage and other statistical indicators. In the remote fire monitoring system, reliability measures can usually be used as reliability QoS indicators, such as the number of backups, active/passive replication, etc.
4.1 Security requirements for data transmission
With the development of the network, network security issues have become the top priority of network administrators and users, and are also an important factor in determining the fate of the Internet. In fact, there have been many individual networks that have been forced to temporarily withdraw from the Internet due to threats to their own security. Similarly, the security of information transmission of the remote fire monitoring system is an important factor in whether the system can operate normally on the Internet.
5 Conclusions
This paper proposes a design of a fire remote monitoring system based on CAN bus and embedded gateway structure. CAN bus has been recognized as one of the most promising field buses. It is favored by more and more R&D personnel due to its outstanding advantages such as high cost performance and simple implementation. The embedded gateway based on DS80C400 has the advantages of high integration, high cost performance and short development cycle. It is increasingly widely used in realizing the access of CAN to Ethernet and Internet [6]. The transmission requirements of fire information on the Internet are analyzed. Literature 5 gives some solutions to solve these requirements, but further in-depth research is needed.
The author's innovation point of this paper:
Combining the characteristics of remote fire information data collection and transmission, the application of CAN bus and embedded gateway technology to the fire remote monitoring system is the main innovation point of this paper.