Research On Coal Mine Gas Density Monitoring System Based On Surface Acoustic Wave Sensing Technology

As a big energy consuming country,China has a huge demand for coal and other mineral resources.Coal mine safety is an important part in the coal production,and gas accident in coal mine is uppermost priority in coal mine safety accidents which has brought large threat to the people's safety and property.With the development of coal mine safety monitoring technology and the urgent requirement of intelligent mine construction,it is very urgent to study a new type of coal mine gas monitoring system for the improvement of coal mine gas monitoring technology.SAW sensor has lots of advantages,such as small size,high sensitivity,low cost,strong anti-interference ability and so on.It is suitable for the future development of coal mine safety monitoring technology,and expected to play an important role in coal mine gas detection.In this paper,the monitoring system of delay line type SAW gas sensor with center frequency of 300M Hz is mainly studied on,and this research consists of two parts:hardware and software.In the research of hardware,we choose the double channel delay line structure to design the gas density monitoring system with the analysis of the detection principle and the detection method of SAW gas sensor.The front part of the hardware circuit includes the high frequency oscillation circuit,mixing and signal processing circuit.The high frequency oscillation circuit is used to generate the 300M high frequency oscillation signal corresponding with the central frequency of SAW sensor.The high frequency oscillation circuit adopts a positive feedback oscillation circuit,in which INA-02186 integrated RF amplifier provides gain and loss of oscillation circuit,and LC phase shifter is used to keep oscillation circuit working stable.Mixing and signal processing circuit reshapes the oscillating signal to square wave signal by mixing the local oscillator signal from the sensitive film port with the reference signal from another port,and then the output signal travel through the low-pass filter,amplifying circuit and reshaping circuit.The mixer adopts the integrated structure,and the AD831 integrated chip is chosen as the mixer to make the system work at low power consumption by design of pins.The 5 order Butterworth low-pass filter is used to remove the unwanted signal.The amplified circuit with 2SC3355 is used to amplify the voltage of the signal processed by filter.Finally,the 74HC14 is used as the core component of the reshaping circuit,which makes the oscillating signal to be square wave,and so it is easy to detect the frequency data.The rear part of the hardware includes minimum MCU system,sound and light alarm,LCD display,SD card storage,USB download,communication circuits and other peripheral circuits.MCU extracts the frequency data of the square wave signal processed by the front part of the circuit,and transforms it to the density value.Sound and light alarm circuit,LCD display circuit,SD card storage circuit,USB download circuit and other peripheral circuits realize the sound and light alarm,display,storage and other operation according to the density data.In the research of software,we use VB as the design programming language,and the upper computer is composed of account management,user operation and data manipulation functions.The communication system between the upper computer and lower machine is made by MSComm.The upper computer has the function of storing density data transmited from the lower machine by establishing connection between ADO controls and ACESS data base,and then calls datagrid to build density data query table in the upper computer.Besides,the RS-485 communication and RS-485 master-slave communication model are used to realize long-distance transmission of sensing data and multi nodes communication to PC for realistic application.At last,the gas density monitoring system terminal with the function of sound and light alarm system is obtained,and furtherly the monitoring terminal is simplified to act as a pure gas density monitoring node without alarm function.This research is significant for the practical preparation of coal mine gas density monitoring system,and also for its pratical application in coal mines.