Apetite

2009 WASE International Conference on Information Engineering

High-speed Data Sampling Based on FPGA and Its Application in Flowmeter
Wang Yuhui Dai Ju Wang Yuhui
Science College Qingdao Technological University Qingdao, China w_yh2000@163.com The flowmeter is new-style software time- difference method ultrasonic flux measurement system; it can be used as measuring high-precision velocity ofliquid, instantaneous flux and accumulative flux. What’s more, it can measure micro displacement, thickness and no-damage probe. Work principle of time-difference method ultrasonic flowmeter A. Work principle Time-difference method ultrasonic flowmeter is widely applied since it has the features that precision is high, sensor construction is simple and not influence liquid flow state. Accordingto ultrasonic measurement theory, we know that ultrasonic transmission speed in liquid is related with liquid velocity. Hereby, flux measurement can be realized. The measurement principle of time-difference method ultrasonic flowmeter is that when ultrasonic transmits in liquid, the time when ultrasonic transmits in the same direction with liquid flows and in reverse direction with liquid flows isdifferent. Concrete formula deduction is referred in reference 1《 flux measurement handbook》. Figure 1 shows the construction principle graph of usual ultrasonic flowmeter sensor. Suppose the angle between ultrasonic transmission direction and pipeline direction is β. Final result expression formula is:
ΔT = T 2 − T 1 L L = − C cos β − V C cos β + V 2 LV 2 LV = 2 = 2 C cos 2 β − V 2 C 2 (cos 2 β− V 2 ) C

College of Information and Electrical Engineering Shandong University of Science and Technology Qingdao, China w_yh2000@163.com
Abstract—The measurement principle and hardware structure of a new-style time-difference method ultrasonic flowmeter are presented. Software arithmetic based on FPGA high-speed data sampling technology is put forward. Sample speed is up to 80MHz and sampledepth is 1K byte, it can fulfill the requirement of ultrasonic flowmeter software arithmetic to sampling. The design can upgrade on-line. Thus, system’s whole performance is improved. Keywords-data sampling; FPGA; flow mete

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INSTRUCTION

Data sample technology is an important composition part of intelligence meter and control instrument. It includes signal process, A/D conversion, datamemory and control timing sequence logic circuits and so on. Usually these circuits are made up of some separate devices, but when the system requires high-speed data sample, since separated device’s integration is low, these devices are highly difficult to match in speed. The design selects FPGA device EP1K30TI144 that possesses ten thousands logic gates and embedded array block (EAB), data buffer,address generator, reading and writing control timing sequence logic and encoding circuits in data sampling circuit are all integrated in one FPGA chip. In virtue of FPGA high-speed, large-scale characteristics, design difficulty is greatly reduced and data sampling system’s integrity and reliability are improved. Moreover, FPGA can realize logic reconstruction and insystem program (ISP). So thesystem possesses the merits that upgrade is easy and development cycle is short. Usually the frequency of ultrasonic flowmeter sensor is 1-5MHz, according to sampling theory, sampling frequency must be up to 2-10MHz. In order to fulfill the requirement of ultrasonic flowmeter software arithmetic to sampling, this design selects 80MHz analog-to-digital converter (ADC) AD9057 to complete A/Dconversion, In device EP1K30TI144, the highest operation frequency of writing RAM is 196MHz., therefore sampling speed is only dependent on ADC (80MHz), the design entirely fulfill waveform record precision request.

Ultrasonic transmission speed C in still liquid usually exceeds 1000 m/s, in this design, the liquid average velocity V of measured liquid doesn’t exceed 10m/s. for V²/C² is much less...