Development Of High Precision Two-Path Gas Ultrasonic Flowmeter Based On DSP

Because the gas ultrasonic flowmeter has many advantages such as high precision,large range ratio,large measurable range,no pressure loss,and measurable two directions flow,it has attracted much attention in the field of flow metering in recent years.Measurement accuracy has always been an important performance indicator of flow meters.Accurately identifying the arrival time of ultrasonic receiving signals and improving the measurement accuracy of gas ultrasonic flowmeters is an important issue in research and development.This topic focuses on the following three aspects:The zero point error and zero drift of the three pairs of transducers of Dayu,Jiakang and Airmar are tested in detail,and the consistency,sensitivity and received signal peak-to-peak discrimination are tested and compared.Finally,the above test results are comprehensively analyzed and compared to complete the transducer selection.The DN50 measuring tube section was designed with two-path chord-parallel installation.In the aspect of accurate time measurement method,the classical double threshold trigger method and the improved principle of double threshold method based on similarity judgment,the wrong wave problem and its defects are analyzed.This paper collects and analyzes the received signals at different flow rates,and proposes a method to accurately identify the characteristic points of the signal arrival time: the characteristic peak extraction method.The anti-interference ability of the three methods is compared by the simulation signal processing experiment.The first two methods have obvious error wave when the SNR is 20 dB,and the characteristic peak extraction method is still effective when the SNR is 10dB;The effectiveness of the method at different flow rates,the first two methods have started the wrong wave when the flow rate is greater than 10m/s,and the characteristic peak extraction method can obtain the desired propagation time more when the flow rate is 35m/s.In the hardware and software design of the measurement system,the power module,ultrasonic analog front end,high-speed data acquisition and transmission module and various software programs are designed.The focus is on the use of high-voltage power supply and high-voltage analog switch to achieve transmitted and received signals switching of two-path in downstream and upstream.It improves the amplitude of the excitation signal while improving the signal-to-noise ratio of the received signal,simplifies the circuit design and ensures the consistency of the transmit and receive circuits.The signal acquisition is realized by a 5MSPS 12-bit ADC,and the characteristic peak extraction algorithm is implemented in the DSP.Based on the above three aspects,this thesis developed a high-precision two-path gas ultrasonic flowmeter based on DSP,and carried out real-flow verification experiments.The measurement error is always within ±1% in the flow rate range of 1m/s~35m/s,while the double-threshold trigger method has a measurement error of more than ±2% above 20m/s;the repeatability is 0.2233% below the boundary flow point,and the maximum value above the boundary flow point is 0.0784%,which greatly improves the repeatability of the single-path ultrasonic flowmeter.