Precise Speed Measuring Technology In Multi-path Ultrasonic Gas Flowmeter

Ultrasonic technology for flow measurement has successfully applied in liquid. Due to the accuracy, stability, no pressure loses, wide measurement range, and low cost, it has become a novel technique in the flow measurement area. However, ultrasonic technology for flow measurement is immaturity in gas. And this technique is grasped just by several companies. The reason is that the ultrasonic sound's transfer characteristic in gas is different from liquid situation. This thesis aimed at finding an appropriate ultrasonic processing method, so the ultrasonic sound's precision speed measurement can be satisfied, and the ultrasonic technology for flow measurement can be applied in gas area.In this thesis, the currently domestic and overseas general developing situations of the signal processing method in ultrasonic flowmeter are summarized. According to the characteristic of the ultrasonic sound transmitting in the gas, the essential properties of these techniques are analyzed, and the problem in the ultrasonic sound speed measurement is been discussed. After comprehensive comparing, an improved polarity correlated arithmetic is put forward based on the cross-correlation theory. This arithmetic setup four cycle standard ultrasonic polar signal, and correlated with the ultrasonic received signal. Then the distributing instance can be educed. This instance shows that the maximal value will be periodicity if there has ultrasonic sound in the received signal. And the cycle is the same to the ultrasonic sound. The maximal value's difference will be also in a small range. If there is no ultrasonic sound in the received signal, the maximal value is not in order. So ultrasonic sound's precision identify can be implement through this orderliness.Based on the analysis of the nation standard"Measurement of natural gas flow by ultrasonic flowmeter", the technical requirement of the ultrasonic sound speed and time measurement in the flowmeter is put forward. Then the main project of measurement system is educed. Its core of hardware system is micro-single-chip AT89S52. The design of the memory expand circuit for AT89S52, ultrasonic driving and controlling circuits, incepting and processing circuit, display circuit and communication circuits are introduced in detail. The design of software based on the function and task of the single-chip is also been discussed. The hardware and software anti-jamming is been analyzed at the same time.The repetition of the ultrasonic sound and the experiment of zero velocity in gas flowmeter are tested using this speed measurement system. The results show that the repetition of the ultrasonic sound is all right, and the identification of the ultrasonic sound is correct, and the system stability is favorable.