Design Of Travel Time Ultrasonic Flowmeter System Based On FPGA Chip

Ultrasonic flow measurement technology, which developed rapidly in recent several ten years, is a new-style flow measurement technology. It uses the liquid velocity information carried by the ultrasonic when it is propagating in the liquid to measure the flow of liquid. The main merits of the flowmeter are non-contact, high accuracy, wide measurement scope, convenience of installation and maintenance, especially acceptable for measurement of temporary flow, large flows, and flow in dangerous environment In recent ten years, on the basis of development of high-speed digital signal processor and microprocessor, on the basis of research for new-style probe material and technology, on the basis of research for acoustic channel configuration and flow mechanic, the ultrasonic flow measurement technology has obtained a great advancement, showing its strong technical advantage and becoming an important flow measurement technology. The paper introduces basic principle and realizing method of the ultrasonic flow measurement technology. On basis of absorbing and referring to the domestic and foreign advanced ultrasonic flow measurement technology, a new high precision time measuring method was presented in order to improve the system precision of time measuring of travel time ultrasonic flowmeter and the whole system hardware is designed and the design idea of the system software is given. Considering the development state and the existent demerits of the domestic ultrasonic flow measurement technology presently, the following several problems are mainly discussed and solved:1. With regard to the problem of system stability and reliability. First, delay window is used to reduce influence of pulse disturbance and signal amplitude to measurement result Second, choose integrated circuit chips and circuit module in the design of ultrasonic signals' emitting and receiving circuits instead of the traditional discrete analog component to improve the stability and reliability of the system. Third, most of digital circuits are integrated into FPGA (Reld Programmable Gate Array) chip of Spartan2E xc2sl00e of Xilinx Company so as to simplify design and to develop the stability and reliability of the system. 2. With regard to the problem of improving accuracy and measurement scope of the system.Hrst, multiple-level amplifiers are used to enhance amplifier dynamic scope. Second, combining the theory of PLL with the technique of edge detecting, the new time measuring arithmetic made the travel time of ultrasonic just consist of integral units of timing pulse, which could minimize the phase error of timing pulse; meanwhile implemented the circular measurement of spread time through logical programming, which could reduce the edge detecting error and system error. Third, flow revision coefficient is studied and analyzed, and calculation formulae of the flow revision coefficient are given in different situations.