Design Of Low Frequency Rectangle Wave Excitation Electromagnetic Flow Meter

Electromagnetic flowmeter, as a main measure instrument, holds great increasing in interior market. The pivotal technology is controlled by some large overseas enterprises as a result of the manufacture of electromagnetic flowmeter is mainly the assembly of key parts imported by internal company. So it is important significance to develop the electromagnetic flowmeter interiorly.This dissertation analyzes the principle of electromagnetic flowmeter, the pivotal technical problems in the process of development and the questions needed to be resolved in the industrialization of products. As these researches being the foundation, rational solving project, practice project and final design are all put forward. Furthermore, the development of electromagnetic flowmeter with low frequency rectangular wave excitation is finally selected as the emphasis of research through analyzing the advantages and disadvantages of the different kinds of electromagnetic flowmeters.This dissertation comprises the following stages: firstly, analyzing the status existed in electromagnetic flowmeter interiorly or overseas; and then analyzing the principle of electromagnetic flowmeter. The conclusion is that inductive electromotive force, gotten from sensor with the distribution regularities of weighting function, is proportional to the average flow velocity in pipe and is not relevant to the distribution of flow velocity when flow velocity is non-central symmetry with the central axis. So electromagnetic flowmeter could solve the question of high accuracy in principles. Thirdly, analyze that the main difficulty of flow signal measurement is the measurement of small signal. The inducted signal is very weak with the micro voltage unit in the actual measure process. This signal is not insulation with the earth, and its internal resistance is very large. So it's easy to lead various interferences into inducted signal. This chapter mainly analyzes the main structure of interferences that affect the signal measurement. Fourthly, according with the analyzing of flow measurement, we research the main problems needed to be solve in the process of measurement, such as analysis and measurement of the internal resistance, selection of excitation frequency, stable signal datum mark and restraining common mode interference, restraining for serial mode interference and working frequency interference; transporting and shielding the flow signal, constant current excitation and magnetic field equalizing, flow measuring...