Abstract: This paper addresses the fire problem of belt conveyors in mines and analyzes its causes, and designs a temperature monitoring system for the conveyor. This paper focuses on the common fault modes and causes of conveyor belts, CAN bus, speed measurement and temperature measurement principles, as well as the protection system and hardware and software design. The system has a simple structure, low cost and good practical performance, and the experimental results meet the expected design expectations. Keywords: AT89S52; CAN bus; conveyor belt; temperature 1 Introduction With the continuous improvement of the scale, mechanization and automation of mines, belt conveyors are widely used in underground coal mines as the main transportation and hoisting equipment. The use of a large number of conveyors underground increases the risk of fire. According to statistics, belt conveyor fires account for about 20% of underground coal mine fires [1.2], and the resulting economic losses and social impacts are incalculable. Conveyor fires are mainly caused by the friction of the belt generating heat and igniting the belt, and the friction of the belt generating heat is mainly caused by the slippage of the belt on the main drum. Therefore, monitoring the slippage and temperature of the drum is of great significance to improving the safety of belt conveyor operation. This paper investigates this problem. 2 Common Fault Modes and Causes of Conveyor Belt Temperature One of the most common causes of conveyor belt abnormalities is roller slippage. According to tests conducted by the Xuzhou Mining Group Company's test station, after 40 minutes of conveyor belt slippage, the surface temperature of the roller can reach approximately 300 degrees Celsius, and the conveyor belt begins to smoke; heating tests showed that this temperature is close to the conveyor belt's ignition temperature. Therefore, roller slippage is extremely dangerous. During slippage, the roller rotates while the conveyor belt does not rotate or rotates very slowly, continuously rubbing against a section of the conveyor belt. When the roller temperature rises to a certain level, it will ignite the conveyor belt. 3 Composition of the Conveyor Belt Temperature Protection System The conveyor belt temperature protection system mainly consists of a CAN bus that communicates with the host computer, a temperature sensor responsible for detecting the conveyor belt temperature, a speed sensor responsible for detecting the conveyor belt speed, and equipment for temperature protection and speed control. The system structure principle is shown in Figure 1. [align=center] Figure 1 System structure principle diagram[/align] 3.1 CAN bus CAN-bus (Controller Area Network) is a bus-type protocol bus. It is safe, accurate, reliable, and resistant to electromagnetic interference. When the signal transmission distance reaches 10km, the CAN bus can still provide a data transmission rate of up to 50kbps. As a technologically advanced, fully functional, and cost-effective remote network communication control method, CAN-bus has been widely used in various automated control systems to realize bidirectional serial communication and multi-node digital communication systems between the production site and intelligent control equipment. The CAN bus has high performance, high reliability, and flexible design. In complex or large-scale applications (such as industrial field control or production automation), it is easy to realize the new control method of "centralized monitoring and decentralized control" in modern industry[3]. 3.2 Infrared temperature sensor Because the temperature probe of the traditional contact temperature sensor cannot be fixed on the surface of the conveyor belt, it cannot detect the surface temperature of the conveyor belt, and therefore cannot fully reflect the temperature generated by friction of the conveyor belt. The infrared temperature sensor used in this system operates on a non-contact principle, allowing for convenient detection of the conveyor belt's surface temperature. It is unaffected by ambient temperature, offers high accuracy, and effectively prevents fires. Its alarm point can be set arbitrarily between 0 and 100 degrees Celsius without sensor adjustment, and the target measurement distance is 0–1200 mm. 3.3 Speed ​​Sensor The speed sensor detects the speed of the belt conveyor, enabling low-speed slippage and overspeed protection. This system uses the 3020T Hall effect switch sensor from the 3000 series manufactured by SPRAGUE, USA. Based on the Hall effect principle, a permanent magnet is fixed to the edge of the turntable of the main roller connected to the motor. The turntable rotates with the measured shaft. A Hall effect device 3020T is installed near the conveyor belt. When the turntable rotates with the shaft, the sensor outputs a pulse signal due to the magnetic field generated by the magnet. The frequency of this pulse is proportional to the rotational speed; by measuring the pulse frequency, the rotational speed can be calculated. 3.4 Temperature, Speed ​​Control, and Protection When the roller is working, its temperature is detected by the sensor and transmitted to the microcontroller, which checks whether the real-time temperature is within the allowable range. First, the conveyor's status is divided into normal and alarm states; each status is displayed on an LCD screen. For abnormal temperatures, the system first checks if the speed exceeds the set range. If the speed is too fast or too slow, the microcontroller adjusts the speed via a DAC0832. The analog output of the D/A converter is proportional to the input digital value; changing the input digital value changes the analog current (voltage) output. In this design, if the conveyor belt speed exceeds the set range, the value sent to the DAC0832 is decreased by 1; if it is below the set range, it is increased by 1. This is processed and displayed by the main program, and the speed is continuously adjusted to control the conveyor belt speed. Information is stored in an E2PROM for fault analysis. When the temperature rises to the warning threshold, the controller alarms and displays the result. 4. Composition and Control Principle of the AT89S52 Control System This system uses the AT89S52 as the microcontroller to form a conveyor belt protection system. The AT89S52 is a low-power, high-performance CMOS 8-bit microcontroller with 8K of in-system programmable Flash memory. In idle mode, the CPU stops working, but the RAM, timer/counter, serial port, and interrupts continue to operate. In power-down protection mode, the RAM contents are preserved, the oscillator is frozen, and all microcontroller operations cease until the next interrupt or hardware reset. Therefore, this microcontroller meets the needs of this design. 4.1 Hardware Design The system mainly consists of an AT89S52 interface circuit, a CAN bus circuit, an alarm circuit, a temperature and speed measurement circuit, an LCD display circuit, and a keyboard circuit. The CAN bus system design uses a host computer and node approach, with communication between the host computer and nodes via the CAN bus. In the host computer design, since the host computer is responsible for the control and scheduling of the entire system and has a heavy workload, a PC+CAN card solution is adopted. The CAN bus controller uses a Philips SJA1000 CAN controller and a PCA82C250 CAN transceiver. In the application of the CAN controller: the SJA1000 is a standalone CAN controller that supports the CAN2.0B protocol. The SJA1000 is mainly responsible for converting parallel data into CAN format for transmission and reception. It has built-in transmit and receive buffers, and features strong error alarms and dual filtering. It also has reduced radio frequency interference (RFI) and strong electromagnetic interference (EMI) immunity. The hardware system framework is shown in Figure 2. [align=center] Figure 2 Hardware Structure[/align] 4.2 Software Design The software consists of a main program, interrupt service subroutines, and functional subroutines. Based on the system's functions, the software is divided into several relatively independent modules. Programs are written according to the flow, and after each module's program is successfully debugged, they are finally connected together for overall debugging. The main program primarily initializes the functional modules, sets the correct parameters for each module, enables interrupts for each interrupt-driven control task, and waits for interrupts to occur. When an interrupt occurs, the interrupt function module is switched, and the interrupt service subroutine is executed. The interrupt service subroutine mainly performs timing functions. The functional subroutines mainly perform temperature and speed reading, writing, judgment, and control. The structure of the system's functional subroutines is shown in Figure 3. [align=center]Figure 3 Control Subroutine Flowchart[/align] After the system is put into operation, the AT89S52 chip of the controller first reads the set standard temperature and speed from the E2PROM. Then, the microcontroller periodically samples the temperature and speed pulse signals of the conveyor belt, where the temperature signal of the conveyor belt is generated by an infrared temperature sensor. The AT89S52 calculates the temperature and speed of the conveyor belt based on the values ​​in the temperature register and speed register, and displays the instantaneous temperature and speed. If the measured temperature and speed are within the allowable speed range, the system continues to scan, compare, and display the temperature and speed of the conveyor belt; otherwise, the microcontroller processes the data, executes alarm control or hysteresis control, and writes the current temperature and speed to the E2PROM via the I2C bus for fault analysis, while preventing data loss in case of power failure, thereby achieving temperature protection for the conveyor belt. 5 Conclusion The system fully utilizes the on-chip and off-chip resources of the AT89S52, making the control system compact and easy to implement. At the same time, the introduction of the CAN bus and E2PROM improves the safety and reliability of the control system, enhances the real-time control effect, and improves dynamic performance. This facilitates correct decision-making by monitoring personnel and greatly improves reliability. Tests conducted on the conveyor system show that the system performance is stable, the actual control effect is good, and the CAN bus system has high reliability and good real-time performance, fully meeting the needs of underground field work. The authors' innovations are: 1. The use of an infrared digital temperature sensor significantly improves the reliability and accuracy of temperature detection. 2. The use of a CAN bus for transmitting digital data underground improves system reliability and reduces wiring complexity. References [1] Kong Lifang, Zhang Hong. Application of CAN bus in transmission of safety monitoring system [J]. Microcomputer Information, 2008.1-2:43-44. [2] Nicholas P C. Troubleshooting method of conveyor belt [J]. Coal Mine Safety, 1991, (4):67-69 [3] Hao Longbiao, Yuan Hongyong. Fire detection and control engineering [M]. Hefei University of Science and Technology of China Press, 1999.1 [4] Du Xianghan. Development of conveyor belt speed protection system with CAN bus function [J]. Industrial and mining automation, 2008 [5] Hu Junjian, Xie Qiyuan. Prospect of composite and intelligent fire detection technology [J]. Fire Science and Technology, 2005, 24 (2):199-201. [6] Liu Huanping. Single-chip microcomputer principle and interface technology [M]. Beijing: Beijing University of Aeronautics and Astronautics Press, 2007 [7] Huang Min et al. Research on fire monitoring system for mine belt conveyors [J]. Journal of Coal Science and Technology, 2002(2).