The Development History of Electromagnetic Flowmeters
Date: 2014-10-28Read: 14
Introduction: In 1832, Faraday used the Earth's magnetic field to measure the flow velocity of the Thames River, but was unsuccessful. This is because there are polarization and thermoelectric effects under a DC magnetic field, resulting in false signals; At that time, the measurement technology had not yet reached the ability to suppress various interference signals and measure high impedance signals; In addition, the riverbed short circuited the flow velocity signal, which led to the failure of this experiment.
In 1930, Williams+E.JElectromagnetic FlowmeterThe working principle of the electromagnetic flowmeter was mathematically analyzed, and a model and experiment were conducted on an insulated circular tube and an electromagnetic flowmeter with uniform magnetic field distribution. This model is very similar to modern electromagnetic flowmeter. He analyzed the non-uniformity of velocity distribution at various points on the cross-section of a circular tube and the influence of fluid conductivity on induced voltage. He pointed out. The induced voltage at the center of the circular tube is greater than that around it. Due to this reason, a circulating current will be generated inside the fluid, resulting in a smaller induced voltage between the electrodes compared to the induced electromotive force generated by the fluid between the two electrodes.
Williams also pointed out that if the magnetic field is strong enough and the conductivity of the measured fluid is high, then the circulating current inside the fluid is very strong. This current will generate an anti magnetic field, affecting the original magnetic field, so that the force between the magnetic field and the fluid cannot be ignored.
After Williams, Kolin. A is known for its expertise in blood flow metersElectromagnetic FlowmeterA lot of theoretical work has been done. He pointed out that if the flow velocity distribution in the return pipe is axisymmetric, the voltage measured between the two electrodes is proportional to the average flow velocity. After World War II, people began using electromagnetic flow meters to measure the flow rate of liquid metal sodium and bismuth. By 1954, electromagnetic flow meters had become a commercially valuable instrument. In 1962, Shercliff J.A. published the book "Theory of Electromagnetic Flow Measurement", summarizing the achievements of his predecessors. In his work, he first proposed the concept of the input weight function.
From the 1970s to the 1980s, due to the rapid development of industry, there was an urgent need to solve the detection problems of liquid-solid two-phase fluids such as slurry and mud, as well as strong corrosive and abrasive media such as hydrochloric acid, nitric acid, and sulfuric acid. This promoted the continuous development and updating of electromagnetic flow meters, resulting in various new types of electromagnetic flow meters such as small and lightweight, integrated, explosion-proof, plug-in, and submersible. The series of varieties with diameters ranging from 1.5mm to 3m are constantly improving, and the output is constantly increasing. Since 1975, electromagnetic flow meters with rectangular wave excitation have entered commercialization and gradually replaced traditional alternating drop excitation methods. In 1987, dual frequency excitation methods began to appearElectromagnetic FlowmeterThe earliest research on electromagnetic flow meters in China began at the Shanghai Institute of Industrial Automation Instruments in 1956. In 1982, China developed the first generation rectangular wave excitation electromagnetic flowmeter, which shortened the gap with industrialized countries. Subsequently, plug-in, small and lightweight, ceramic, and electromagnetic flow meters with microcomputers were successively developed.