Design And Implementation Of Digital Transit-time Ultrasonic Flowmeter

Molten salt reactor uses molten salt as coolant and fuel carrier which is corrosiveand running at high temperature. Clamp-on ultrasonic flowmeter is an ideal solutionto solve the problem of high-temperature and corrosive fluid flow measurement.Research on high-temperature ultrasonic flow measurement was conducted to masterrelated core technologies and solve the problem of molten salt flow measurement.This paper studies the design and implementation of digital transit-time ultrasonicflowmeter. It covers the operating principles, electronics design and signal processingalgorithms of digital transit-time ultrasonic flowmeter. Accordingly, hardware andalgorithm solutions are given.The hardware mainly includes three parts: ultrasonic analog front-end(AFE),digital processing part and data acquisition part. Ultrasonic AFE performs ultrasonicsignal sending and received signal conditioning; Digital processing part is based onTMS320F28335DSC(Digital Signal Controller) which possess not only the controlfunction of MCU but also the processing ability of DSP. It can be used to control themeasuring procedure and run the signal processing algorithms in our design; Dataacquisition part performs the digitalization of ultrasonic signals with the aid ofhigh-speed pipelined ADC and the existing mechanisms and resources of F28335.Algorithms mainly involve transit-time difference measurement and transit timemeasurement. Transit-time difference measurement algorithm is implemented tocalculate the transit-time difference of upstream and downstream signals based oncross-correlation algorithm. The measuring accuracy of using the sole peak positionof discrete cross-correlation function to determine the time difference depends onsampling rate. Increasing sampling rate on a vast scale does not mean a good choicein to reduce measuring error. The use of cure fitting algorithm on the base of peakposition of discrete cross-correlation function can achieve high measuring accuracywithout large cost of data acquisition and processing. Transit time measurementalgorithm is implemented to calculate the transit time of ultrasonic signal in fluidbased on Hilbert transform and wavelet transform.At last, we tested our prototype of flowmeter on the water flow calibrationplatform. Test results show that the relative error of flow indication of our design is±0.67%, within the requirement of class one meter standard. Then, the practicalon-line tests were performed in the high-temperature molten salt (nitrate) pyrologytest loop. The comparative experiments showed that the prototype works well under the actual working condition, and the preliminary results are in accordance with theindications of the imported flowmeter made by Flexim. This paper gives detailedanalysis of digital transit-time ultrasonic flowmeter, provides important methods andplatform for high-temperature ultrasonic flow measurement research. The prototypeflowmeter has laid a good foundation for further research and development.