Design of underground multi-parameter monitoring system based on CAN bus

Monitoring underground production parameters includes monitoring harmful or dangerous components in mine air, the physical state of mine air, the operating status of ventilation equipment and other parameters. General monitoring objects include gas, wind speed, negative pressure, temperature, liquid level, etc. The working environment of underground production parameter monitoring is harsh, the monitoring points are scattered, the monitoring types are many, the number of measuring points is large, the communication distance is long, and the real-time and reliability requirements are extremely high. Therefore, it is very necessary to develop a multi-parameter intelligent monitoring system for underground coal mines with reliable performance and low cost. The author uses the currently popular virtual instrument technology to realize the interaction with the host computer, and takes advantage of the low cost, high integration, and easy communication with each other and computers of the single-chip microcomputer to develop a new type of underground multi-parameter intelligent monitoring system.

2 Overall system design

The underground multi-parameter intelligent monitoring system consists of a monitoring substation system, a CAN bus communication system, an upper human-computer interaction (monitoring computer), and a coal mine safety expert system (database query server). The system structure diagram is shown in Figure 1.

2.1 Monitoring substation system

The monitoring substation system uses a high-performance ATmega48 microcontroller as the main control device, and is connected to multiple gas, displacement, pressure and other sensors. After passing through the external analog circuit, the data is sent to the microcontroller's built-in high-precision A/D converter to achieve real-time acquisition of multiple analog quantities, and to achieve data exchange with the upper human-computer interaction through the CAN bus communication system. In addition, the monitoring substation can also realize underground sound and light alarms when gas, pressure and other parameters exceed the standard, and perform corresponding control operations according to the upper human-computer interaction commands, effectively avoiding accidents.

2.2 CAN bus communication system

The main function of the CAN bus communication system is to realize data communication between multiple monitoring extensions and the upper human-computer interaction (monitoring host), and to transmit the real-time collected analog data through the CAN bus.

2.3 Upper-level human-computer interaction

The human-computer interaction system uses Lab Windows/CVI virtual instruments as the development platform, and utilizes graphical soft panels, rich digital signal processing libraries and advanced function analysis library resources, with the help of the powerful functions of computers to achieve functions such as data exchange between control information and acquisition information between boards, historical data analysis, and data curve simulation.

2.4 Coal Mine Safety Expert System

The coal mine safety expert system uses Microsoft Access 2003 as the development software. The various analog parameter indicators and the operations that need to be adopted to avoid accidents in specific situations are summarized for the human-computer interaction system to query. The human-computer interaction system sends corresponding control commands based on the query results, thereby minimizing accidents.

In addition, the system will also print out analysis reference opinions for ground station personnel to query so as to facilitate real-time improvements.

3 Monitoring Hardware Design

The main control device and peripheral circuit of the monitoring system are shown in Figure 2, where the peripheral circuit includes CAN bus communication circuit, MAX1232 external watchdog circuit, 8-channel analog quantity acquisition circuit and time-sharing gating device 4051 circuit, etc. Any analog quantity acquisition circuit is shown in Figure 3.

When used together with Figure 2 and Figure 3, the monitoring system can monitor up to 48 analog signals, greatly expanding the acquisition range. It also uses a high-precision 10-bit A/D converter built into the microcontroller, which simplifies the circuit while ensuring its monitoring accuracy and speed. Its working principle: Connect the sensor to (J1). When the sensor parameters change, the analog acquisition circuit amplifies the signal, passes through the RC filter circuit, and sends it to one channel of 4051. After being selected by the microcontroller, it is sent to the microcontroller A/D converter to obtain the A/D conversion value. The microcontroller sends this data to the upper human-computer interaction through the CAN bus device chip. The human-computer interaction (monitoring host) compares this data with the safety value. If the change is not large, it continues to monitor; if there is a large deviation, it passes this information to the expert system. After analysis, the expert system obtains the corresponding operation instructions and feeds them back to the human-computer interaction (monitoring host). The upper human-computer interaction then passes the control information to the microcontroller. Thus, corresponding operations are generated to ensure underground safety.

4 Monitoring system software design

The software design of this system mainly consists of expert system, upper human-computer interaction and monitoring extension subsystem. The expert system is developed with Microsoft Access 2003, which collects a large amount of analog parameter information that needs to be monitored underground for reference by the monitoring host. The upper human-computer interaction uses NI's LabWindows/CVI, which has a friendly interface and uses less instrument hardware and computer resources to replace a variety of high-end data recording and analysis instruments. The computer can automatically analyze data and output reports, which greatly improves the intelligence and test efficiency of the system, reduces the impact of human operation errors on the test results, and provides users with rich functions through a friendly human-computer interaction interface.

In order to make the single-chip system have better real-time performance and code optimization, the software design of the monitoring extension system is written in assembly language. Due to space limitations, only the software design of the upper human-computer interaction and monitoring extension subsystems is briefly introduced here.

4.1 Monitoring extension subsystem

The program flow chart is shown in Figure 4. As can be seen from Figure 4, the monitoring system can realize multiple functions, including multi-channel analog A/D acquisition, data temporary storage, LCD display, interactive communication with the upper human-computer interface, and switch output. When designing, the modular concept is adopted to simplify the design and improve efficiency.

4.2 Monitoring extension subsystem

In order to facilitate code reuse, virtual instrument software development adopts a layered design, which is divided into the main program control layer, human-computer interaction layer, data processing layer and instrument driver layer.

The instrument driver layer is a driver function library compiled for different hardware. It completes the connection between the I/O hardware interface and the processing layer, and is an important guarantee for realizing the independence of high-level software from hardware. The data processing layer parses and calculates the user's operation in the background and sends the control word to the hardware driver layer. At the same time, it realizes data acquisition control, signal analysis and processing, data management, calibration procedures, test report generation, etc. The human-computer interaction layer completes the human-computer interface interaction, responds to user operations, realizes data display, communicates with the expert system to exchange information, and prints reports. The main program control layer is used to organize the coordination of various parts to jointly complete the test task. The Windows multi-threading technology is used in this test software to realize data acquisition and processing, data display at the same time.

5 Conclusion

At present, the underground monitoring system has been verified. Experiments have proved that it has the following characteristics: compared with similar products, it has the characteristics of high precision, strong reliability, stable working performance and low cost; it adopts single-chip control to simplify the structure of the test equipment, reduce the fault link, and improve the work efficiency and intelligence; the test system adopts 10-bit high-precision A/D converter and automatic data report to improve the measurement and control accuracy of the system and reduce the human random error; it adopts virtual instrument as the human-computer interaction interface, integrates traditional test methods and modern computer technology, and improves the intuitiveness and operability of the test system; the expert system integrated in the system can solve the problem through the real-time query function of the fault solution, which reduces the accident rate on the basis of improving efficiency.