Research Of Micrometeor Electromagnetic Flowmeter

The micrometeor electromagnetic flowmeter is used to measuring electric liquid, which uses Faraday law of electromagnetic induction. The flow signal is weak and the interference signal is strong. These cause measurement error is large. Hence, how to pick-up flow signal from many interference singals to realize micrometeor measurement is the emphasis of the micrometeor electromagnetic flowmeter research.At present, the peak value sampling-keep signal processing technology is used common, but it blocks the measurement lower limit to enlarge. So we research narrowband filter signal processing technology. The amplified signal passes narrowband filter to filter high harmonic and pick-up baseband wave.Then the noise power bring down with bandwidth down and improve the signal-to-noise ratio. Because of inductive electromotive force of the high harmonics were filtered out, the baseband signal flow signals contain baseband wave and baseband differential noise. But the phase is 90o , the demodulation signal pulse synchronize baseband wave and orthogonalize the differential fundamental noise. Through the phase-sensitive demodulator, the differential noise can be effectively removed, phase noise apparently disappeared. Then by low-pass filtering and DC amplification, we can receive flow signals. The use of differential amplifier circuit in pre-amplifier can improve the input impedance, reduce the precision resistor matching requirements and improve common-mode interference suppression capabilities.Secondly, in the excitation-driven part, we design constant mean excitation current source circuit. In each period , the mean value of current is constant. Narrowband filter meet the requirements of generation constant magnetic field. Mean constant current source circuit through sampling and comparing achieve the closed-loop feedback regulation. When the voltage changes, there is current charging or discharging on the capacitor. By the integral regulator’s feedback, the voltage of sampling points change, achieving steady flow adjustments and overcoming voltage fluctuations. By the theoretical analysis of authentication, using the current source for micro-meteor electromagnetic flowmeter sensor coil excitation can improve the temperature stability and measurement accuracy. In addition, after the signal was processed, the flow signal convertes into digital signal through the double-integrating A/D converter ICL7135, then sent to microprocessor AT89S52 processing, and then by the built-in graphic LCD display module HD61202U display the result. The keyboard can be used for control. At the same time, we use RS-485 to realize communications with the outside world.Finally, the micrometeor electromagnetic flowmeter test verifies the feasibility of narrowband filter signal processing technology in micrometeor measurement.