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Based on the principle of time difference method and the design concept of high precision, the measuring principle together with the improvement of the calculation method of the time difference method were investigated, aim at the problems of high complexity of the circuit and the inadequate precision of the traditional ultrasonic flowmeter that require pipeline modification. To promote the precision accuracy of the ultrasonic flowmeter to 0.5％, the function principle and its related structure of highprecision timing chip, TDC-GP22 (Time-to-Digital-Converter) were elaborated; and the design of hardware circuit and the working process of the system were introduced. The cause of signal attenuation was analyzed and the amplifying circuit for transmitting signal was designed. Finally, a flowmeter system design based on ATmega single chip and high-accuracy timing chip TDC-GP22 was proposed.

A high-precision marine ambient noise sound pressure monitoring system is developed based on the Michelson interference, a method of improving the measurement accuracy is presented by signal modulation and compensation. Experiments show that the monitoring system has a wide dynamic range and high accuracy especially in low-frequency.

In this paper, to eliminate the mechanical sensors, a sliding-mode observer is designed to identify the speed of permanent magnet synchronous motor (PMSM) based on a field-oriented control system. The results of simulation by Simulink indicate that the speed could be estimated and adjusted precisely. The three-phase current and torque of the motor also have a good dynamic response.

We investigate the spatial coherence of underwater infrasonic noise using a yearlong time series measured by hydrophones moored off Ascension Island. Qualitative agreement with observed cross-correlations is achieved using a simple range-dependent model, constrained by earlier, active tomographic studies in the area. In particular, the model correctly predicts the existence of two weakly dispersive normal modes in the microseism frequency range, with the group speed of one of the normal modes being smaller than the sound speed in water. The agreement justifies our interpretation of the peaks of the measured cross-correlation function of ambient noise as modal arrivals, with dispersion that is sensitive to crustal velocity structure. Our observations are consistent with Scholte to Moho head wave coupled propagation, with double mode conversion occurring due to the bathymetric variations between receivers. We thus demonstrate the feasibility of interrogating crustal properties using noise interferometry of moored hydrophone data at ranges in excess of 120 km.