The Research Of Electromagnetic Flow Meter Bases On Low Frequency Rectangular Wave Excitation

Electromagnetic flow meter is a velocity type flow meter, which bases on Faraday’s induction law. It is used in industrial field widely. Since always, the mode of excitation and the signal processing technology are the determinant for the accuracy and the stability of the electromagnetic flow meter measurement. Currently the electromagnetic flow meters generally adopt the rectangular excitation mode. Although this excitation mode can overcome the electrode polarization effect by direct current excitation mode and the differential interference by sine wave excitation in50Hz. But the electrical level mutation and the excitation frequency also can make the excitation mode produce differential interference and in-phase interference. It decreases the accuracy and the zero point stability.In order to solve the problem, the author proposes a new method about the signal processing bases on the low frequency rectangular excitation mode. It is that the signal has a filtering preprocessing when it comes out from the sensors, then it is amplified by the signal amplifier. After passing the high pass filter and low pass filter, the high-frequency interference and low-frequency interference will be eliminated from the signal. And we will get a better result from the sample data.For the conceptions mentioned above, the author develops the low frequency rectangular excitation system and the following works are completed in the thesis.1. The basic theory, development history and the technology status are introduced in detail through scanning the related documents and books which come from internal and overseas. The author proposes a new method of the signal processing which bases on the low frequency rectangular excitation mode.2. Analyze the mathematical model about the signal of low frequency rectangular wave and use the Matlab to simulate the signal process. The conclusion acts as the theoretical basis for the hardware system design. Complete the hardware circuit design of the low-frequency excitation system which bases on MSP430, including the design of signal process and other peripheral circuits.3. Analyze the excitation system of electromagnetic flow meter bases on finite element analysis by ANSYS. Simulate the work process of the electromagnetic flow meter through building the excitation system model and defining the material properties, and then get the right conclusion that the fluid velocity and the induced voltage are proportional. Second, through the hardware system, many experiments are completed which bases on the excitation system of the low frequency rectangular wave in different excitation frequency and different sampling mode. Then compare the relative error on different experimental results, it proves that the low frequency excitation mode achieves a relatively good result in improving the measurement accuracy of electromagnetic flow meter.