| The flow-meter in which a floater can ascend or drop in a vertical taper pipe with the changing of flux. This flow-meter is a volume flux meter measuring the flux though changing the area of the floater and the vertical taper pipe ,it is also called rotor flow-meter. In America and Japan, this flow-meter is usually called variable area flow-meter. The principium of this variable area flow-meter came forth in 1960s, in the beginning of the twentieth century the first merchandise appeared. Relevant data indicated that in 1985 the proportion of variable area flow-meter took up 19.2% of all kinds of flow-meters in Britain. In our country these years, the production and the applications of variable area flow-meter are also rising obviously.This thesis will research into these problems.In chapter one, the thesis expounds the recent development in flow measuring, describes the operational principle and structure. The thesis also introduces HART protocol in brief, and introduces several kinds of field-bus in common use presently. The thesis indicates that the HART protocol provides a uniquely backward compatible solution for smart instrument communication as both 4-20mA analog and digital communication signals are transmitted simultaneously on the same wiring. Technical proposal is also given in this chapter.In chapter two, the thesis narrates how to collect and dispose the signal of flux, which includes the choice of new magnetic angular displacement sensors, the amplitude adjustment circuit and the method of digital filter. This thesis also introduces several methods of realizing linearity of signals with micro-computers. The method of inserting data by subsection linearity is the most appropriate.In chapter three, the thesis expounds how to design the metal variable-area flow-meter of 4-20mA analog signals. With the beginning of introducing the criterion of two-line 4-20mA, the thesis describes the low-power realization by using modern...
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