Ultrasonic flow meter has been widely applied in the area of meteorology, petroleum, chemical engineering, medicine, water resources management and so on, owing to its advantages of high-accuracy, non-blocking measurement, easy installation and low cost. The A/D conversion circuit design is the core of the data acquisition system for high-accuracy ultrasonic flow meter. According to the data acquisition issues of high-accuracy ultrasonic flow meter in time-difference method, a two-channel 12-bit low-power monolithic CMOS analog-digital conversion ADC12DL040 chip and ARM microprocessor LPC2138 was adopted to design the data acquisition system. The time-difference ultrasonic flow meter theory was described in this paper, the A/D chip and ARM design circuit were given, the hardware structure and software flowchart have been presented. The experimental results showed that the designed A/D conversion circuit be able to reach the resolution of 1~2 ns,the minimum resolution time is 0.305ns, the resolution in nanosecond level for the time-difference of ultrasonic wave propagating between downstream time and upstream time have been reached. The production cost was reduced owing to the designed A/D conversion circuit. Generally the design and implementation of A/D conversion circuit lay the solid foundation for the high-accuracy ultrasonic flow meter.
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