Design Of Ultrasonic Flowmeter For Pipeline Gas Transmission

The use of ultrasonic technology to detect industrial pipeline flow is a newly developed flow measurement method,which has the advantages of application to a wide range of pipe sizes and no special requirements on the transmission media.For the present,the developed ultrasonic flowmeters with practical applications in China and foreign countries have been mainly devoted for measuring the liquid flow,while a small number of them were used for measuring the gas flow in pipelines.Because the ultrasonic wave is largely attenuated in the air and easily affected by environmental disturbances,it is difficult for using the existing ultrasonic detection methods to guarantee the measurement accuracy,therefore appealing for further improvement on the measurement accuracy and stability.Based on the time difference principle for ultrasonic measurement,this thesis proposes a new X-type sensor design scheme and correspondingly,develops a new type of ultrasonic flowmeter for gas detection.Firstly,the detection principle of the traditional Z-type ultrasonic sensor is introduced,and subsequently,an improved X-type sensor mounting method is proposed.The advantages of anti-jamming and improvement on the measurement accuracy are analyzed in comparison with the traditional sensor mounting method.Then,a new ultrasonic flow meter design scheme is proposed.In the hardware circuit design,a high-voltage excitation method is used to overcome the problem of large attenuation rate of the ultrasonic wave in gas,so as to increase the flight distance of ultrasonic wave.In the circuit of receiving signals,multistage amplification is used to amplify the received ultrasonic wave.Meanwhile,an active band-pass filter is designed to improve the anti-noise performance.In the sequel,a circuit simulation software is employed to carry out system simulation and debugging of the calculated circuit component parameters.According to the simulation results,the circuit component parameters are set to meet with the design requirements.By using a threethreshold circuit to rectify the detected point of the received ultrasonic wave,the measurement error arising from the ultrasonic wave loss and/or notch can be reduced,and therefore,the measurement accuracy can be further improved.In the aspect of signal filtering,the wavelet threshold filtering method is used to digitally filter the measured flight time of ultrasonic wave.An MALLAT fast algorithm is adopted to implement the wavelet analysis on a singlechip microcomputer for real-time application.The wavelet signal sequence is constructed by using the symmetrically added floating data window method,which can guarantee online wavelet analysis of the real-time collected data.Moreover,the symmetric expansion method is used to extend the data set,thus overcoming the effect of boundary truncation on the result.For the detected flight time of ultrasonic wave,the digital filter processing is performed,where the Symlets is selected as the wavelet generating function.The processed effects are compared and analyzed under different parameter settings.Experimental tests were performed on the exhaust pipe of a fluidized bed for drying crystals,and comparions with a vortex flowmeter made by E+H company in Germany.The experimental results show that the ultrasonic flowmeter designed in this paper can achieve better measurement accuracy and application stability.