Research And Design Of Wide-beam Transit-time Ultrasonic Flowmeter

Ultrasonic transit-time flowmeters are widely used in industry because of their high resolving power and expedience, but the range of receiving signal is limited when the traditional narrow-beam technique is adopted and the position of receiving beam is sensitive to the environment temperature, so that there are difficulties in process of installation and measurement. Wide-beam technique is a solution to the trouble. Therefore, research of wide-beam ultrasonic transit-time flowmeter is significative not only to industry but to measurement technology.A pipe-Lamb-wave theory is put forward in this paper according to the characteristic of pipe flux measurement. After a physical model of wide-beam path in pipes is designed, the frequency equations for Lamb-wave in pipes are derived in detail. Furthermore, a method of how to engender the Lamb-wave in pipes is proposed.Hardware and software of a wide-beam ultrasonic transit-time flowmeter are designed in this paper. Open-window means and signal-memory are two kinds of original technique in hardware design. Because of its high-speed and the capability for signal-processing, a TMS320F240 DSP is chosen as the core of hardware. A MCU, CPLDs and other circuits and chips are included as its auxiliaries. Besides the velocity and flux display, a current and a OCT output signal are available. The whole system is stead-going and the operation is convenient and intelligent.Four different filters are introduced in signal-processing and the system can adopt different algorithm according to the different flux-state automatically and in time, so that the system has an excellent performance in stability and real-time capability. A model of zero-error is constructed on base of several experimentations, according to which, a new dynamic zero-error compensate method replaces the traditional hardware compensate means in this system. After the signal-processing and compensate, the final measure result is smooth, real-time and accurate.At last, a new timing method is introduced in this paper, it can timing a high-frequency signal with a low-frequency clock. A realization scheme is presented accordingly.