Research On Hardware System Of High Frequency Sine Wave Excitation Electromagnetic Flowmeter

Electromagnetic flowmeter,based on Faraday's law of electromagnetic induction,is a kind of instrument to measure the volume flow of conductive liquid,which is widely used in process industry,municipal engineering and other fields.At this stage,electromagnetic flowmeters mostly adopt rectangular wave excitation,and the excitation frequency is generally not high.In the measurement of solid-liquid two-phase flow,when the solid particles collide with electrodes,the non-stationary slurry interference with 1/f distribution is generated,which cannot be accurately measured by traditional low-frequency excitation electromagnetic flowmeters.The sine wave excitation electromagnetic flowmeter can appropriately increase the excitation frequency and improve the signal-to-noise ratio of slurry flow measurement,because it does not need to extract the flow signal in the excitation steady stage.Foreign companies introduced high-frequency sine wave excitation electromagnetic flowmeters that can measure slurry flow,but no specific technical details are disclosed.Domestic sine wave excitation electromagnetic flowmeters generally use power frequency or low frequency excitation,with low measurement accuracy.In order to develop a high-performance high-frequency sine wave excitation electromagnetic flowmeter,this dissertation carried out the following research work:(1)An excitation drive module based on LCR series resonance was developed.The sensor excitation coil model is analyzed.According to the inductive characteristics of the excitation coil,a capacitor is connected in series in the excitation circuit to make the excitation circuit work in a resonance state,and reduce the power consumption of the excitation circuit.The current source excitation is adopted to avoid the influence of environmental factors such as temperature on the excitation system and enhance the anti-interference ability of the excitation system.(2)A high-performance signal conditioning acquisition module for high-frequency sine wave excitation was developed.The input sensor electrode signal,excitation current signal and coil voltage signal are first differentially amplified and fourth-order low-pass filtered,and then sampled with high precision by a 24-bit ADC.(3)A DSP-based high-speed signal processing and control module was developed.Using TMS320F28335 DSP as the core of digital processing and control to ensure the real-time performance of complex flow algorithm calculation.SARAM storage circuit has been expanded to meet the needs of data storage.In order to investigate the performance of developed high-frequency sine wave excitation electromagnetic flow measurement system,it was matched with the DN40 sensor to carry out the flow rate simulator calibration experiment and the water flow calibration experiment respectively.Results of the flow rate simulator calibration experiment show that,when the excitation frequency is 75 Hz and the flow velocity is 0.2 m/s ?5.0 m/s,measurement error is within ±0.5% and the repeatability is not higher than 0.1,which meets the measurement accuracy of 0.5.The results of water flow calibration show that,when the excitation frequency is 75 Hz and flow velocity is 0.5 m/s?5.0m/s,measurement error is within ±0.5%,the repeatability is not higher than 0.15,and the accuracy level reaches 0.5.When the excitation frequency is 125 Hz and the flow velocity is 0.5m/s?5.0m/s,the measurement error is within ±0.5%,the repeatability is not higher than 0.15,and the accuracy level reaches 0.5.When the excitation frequency is 243 Hz and the flow velocity is 0.5m/s,measurement error is within ±2% and the repeatability is not higher than 0.6.When the flow velocity is 1.0m/s?5.0m/s,measurement error is within ±0.5% and the repeatability is not higher than 0.1.