Application of Correlation Method in Ultrasonic Flow Measurement Based on Time Difference Method

Presently, ultrasonic flow meter is widely used in measurement of the big diameter flow with its own advantages, but it is rarely used in small diameter flow measurement. When using the time difference principle in an ultrasonic flow-meter, the accuracy of the measured time difference directly affect the measurement precision and the measurement range of the meter. The paper introduces a device of ultrasonic flow measurement based on time difference. The device is used to measure the flow of circulation cooling water for blast-furnace, where diameter is small, flow rate is low, and fluid is single-phase. In order to overcome die insufficiency of the ultrasonic flow meter for measuring small diameter flow in the short traveling time of ultrasonic wave, the U-shape installation is used to prolong the transmitting distance. The accuracy and real- time performance are the most important goals here. However, it is difficult to achieve the goals. Because the received signal's waveform and its amplitude value will change with the flow of medium and environment, the exact arrival time of received signal cannot be determined only by comparison circuit. As a result the accuracy of time difference cannot be assured, and the accuracy of measurement system cannot be guaranteed, either. The paper uses cross-correlation algorithm to analyze received signal wave, combining with comparison circuit, and then has realized a precise measurement of time difference. The hardware of the design is based on Mono-Chip Computer AVR, AD9057 and CPLD. It can meet the real-time requirement of the algorithm implementation for hardware. Compared with the traditional ultrasonic flow meter, the system has better stability, precision and practicality.