The Design And Implementation Of Multipath Ultrasonic Gas Flowmeter For Coal Mine

Gas drainage monitoring and metering system is essential for the gas drainage wells to prevent the gas accidents.Compared with traditional mine gas flowmeters,ultrasonic gas flowmeters,which is an ideal instrument for gas extraction detection,have non-block parts,high measurement accuracy and no pressure loss and so on.Ultrasonic gas flowmeter contains two types,i.e.mono-channel and multi-channel.The multi-channel ultrasonic gas flowmeters can reduce the problems caused by uneven distribution of gas velocity in the pipeline.Therefore,it is more suitable for gas extraction measurement than mono ultrasonic gas flowmeters.However,with the late research history on high-precision multi-channel ultrasonic gas flowmeters,there are still many gaps in China's technology accumulation compared with foreign advanced levels,especially in the field of coal mine gas measurement.Therefore,it has practical significance to study the optimization design of measurement system and multi-channel mine ultrasonic gas flowmeter.According to the analysis results of mine measuring environment,this thesis proposes a design scheme of four-channel mine ultrasonic flowmeter with adopts STM32F407 microprocessor as the core device based on time difference detection theory.Meanwhile,in order to correct the error of ultrasonic transit time measurement caused by large received signal interference and serious distortion under the complicated gas drainage environment,a special double threshold level comparison method is proposed to measure the ultrasonic transit time based on the zero-crossing detection technology,and verify the flow measurement experiment.The main research work of the thesis is summarized as follows:1.Combining actual measurement environment,the thesis proposes a system design of measurement based on STM32F407 microprocessor with enhanced DSP processing instructions and floating-point computing ability.And the ultrasonic transit time is measured by the double threshold level comparison method proposed in this thesis.The method first checks whether the ultrasonic echo signal is distorted or not,then determines the ultrasonic transit time according to the established method on the echo signal with good waveform.And verified its feasibility through experiments.2.This thesis has completed some circuit design in hardware implementation,such as the ultrasonic drive signal circuit,the ultrasonic receiving and conditioning circuit,the multi-channel switching circuit design and the functional module circuit design necessary for industrial application.Then,design,the idea of each module circuit is explained in detail,and given the schematic diagram of circuit design.Furthermore,the software system workflow and software function module are described in detail in the software design.3.After completing the system software and hardware design,the zero flow reading experiment and the real flow calibration experiment are performed on the prototype based on the standard table test environment.The simulation results show that the four-channel ultrasonic gas flowmeter system designed in this thesis can operate stably and accurately,and achieve the expected design goals.