Research Of Ultrasonic Gas Flowmeter With Time Difference Method Based On FPGA

Ultrasonic flow meter is an instrument used for measuring different kinds of flow. It is possible to get the fluid medium speed by analysis the message of the ultrasonic for the speed message of the fluid medium is included in the ultrasonic. Ultrasonic flow meter is now widely used in industry for the advantage of non-contact, high accuracy and maintain simply. With the rapid development of science and technology, ultrasonic flow meter is become important study object and get rapid development, but it is still had a lot problems need to be solved in the field of gas measurement, especially at accuracy and stability at low flow.By reference to a large number of literatures, the gas ultrasonic flow meter precision is not high is due to the relatively high risk of miscarriage of justice appeared in the distinction between ultrasonic signal and clutter signal, on the other hand, the lower accuracy of measurement system in the measurement of ultrasonic propagation time is leading to the error of the measuring time.In order to meet the need of design, several improvement methods are taken in gas ultrasonic flow meter system. At first, we use higher integration FPGA to take place of traditional architecture model of single chip microcomputer with CPLD. The system is become simple and rapidity. The second is the problem of temperature influence on the flow meter accuracy is solved by the improved method of time difference algorithm. Then the ultrasonic signal and noise are well separated through amplitude- frequency double judgment technology. At the same time, the precision of flow meter is further improved by using the pulse counting method and the method of combining the edge detection technology. At last, the ultrasonic flow meter become more precise and more stability by reducing noise to reconstruction signal through wavelet threshold de-noising processing technology.Based on above improvement aspects or innovations, the prototype of gas flow meter is made and actual pipeline gas experiments are also completed. The experimental results show that the ultrasonic flow meter has the characteristic of good repeatability and high precision. The expected target of the subject is achieved and will have good market application prospect.