Software Development Of Two Kinds Flow Transmitter Based On Electromagnetic Principle

Key technical problems in two types of measuring instruments based on the electromagnetic principle are studied.These two types of instruments are:electromagnetic flowmeter and electromagnetic vortex flowmeter.Electromagnetic flowmeter has been widely used to measure the flow of conductive media,such as water flow,due to the advantages of no obstruction in the measurement tube and moving parts.A DSP based electromagnetic flow transmitter with high performance is developed so as to implement high frequency magnetic field excitation and digital signal processing methods in real time for improving the measurement accuracy of water flow and measuring the slurry flow,and at the same time to equip a dot matrix LCD for showing more content and to configure the communication interfaces for exchanging information with upper computer.A comb-shaped band-pass filtering algorithm is adopted to process the signal of water flow,and a signal reconstruction method is proposed to deal with the signal of slurry flow.The resources of the DSP chip are reasonably and fully utilized,and the hardware system is designed to realize various functions of the instrument.The timing between excitation control,signal processing,man-machine interface,and data communication is skillfully and flexibly arranged,and the software of DSP is developed.A 20ms timer interrupt is configured,and interrupt nesting is opened in its interrupt service routine so as to ensure real time of both exciting control and signal processing.The liquid crystal refresh display subroutine and the key operation subroutine are put in the main loop in order to make other modules normal execution.The developed software of DSP is suitable for measuring water and slurry flow under rectangular or three value excitations.The algorithm test in real time and water flow calibration experiment are conducted for the high performance electromagnetic flow transmitter,and the experiments proved the effectiveness of the developed software system.The output signal of the electromagnetic vortex flowmeter is not affected by the vibration of the pipeline and the surrounding vibration sources,and its measurement reliability is high and there is no zero point drift.There are large measurement errors in electromagnetic vortex flowmeter when measuring conductive liquid flow mixed with gas,because the existed signal processing method is adopted to obtain the wrong flow signal frequency.For this reason,an algorithm based on signal differential and fast Fourier transform(FFT)spectrum analysis is proposed to calculate the correct frequency of the flow signals.It can amplify high frequency signal and suppress interference of low frequency bubble noise,in order to make the energy of flow signals in whole is dominant.An electromagnetic vortex flow transmitter based on DSP is developed,and an experimental process are designed to perform gas-liquid two-phase flow experiments.The testing results show that when gas volume fraction does not exceed 3.9%,the measurement errors of the transmitter are smaller than ± 3%,which reduces the conductive liquid flow measurement error.