与被测电解质液体接触的金属电极会发生电化学反应(也就是电极材料腐蚀的过程)，电极上会产生极化电压。 Electromagnetic reactions between the electromagnetic flowmeter and the metal electrode in contact with the electrolyte liquid being measured (that is, the process of electrode material corrosion), and a polarized voltage will be generated on the electrode. When the metal material reacts electrochemically with the medium, an oxide protective film is formed on the surface to balance the electrochemical reaction. When the slurry containing solid particles or fibrous fluid flows through the electrode, the protective film on the electrode is rubbed to break the balance of the electrochemical reaction, and the protective film on the electrode surface is to be re-formed.化 Voltage.
衬里表面使得聚集电极附近的电荷跟随移动，于是在电极上感应出变动的极化噪声。 The fluid flow rubs against the surface of the lining of the electromagnetic flowmeter so that the charge near the collecting electrode moves with it, so that a variable polarization noise is induced on the electrode. Obviously, if the dielectric constant of the medium is high, the displacement current is large, and the electric charge moving near the electrode is also increased, and the flow noise increases as the dielectric constant E of the medium increases. According to the application conditions of the electromagnetic flowmeter, the condition for ignoring the displacement current is we / σ << 1. It can be seen that as the fluid conductivity σ decreases, the displacement current will increase. The fluid conductivity σ is inversely proportional to the voltage of the flowing noise. In a highly viscous fluid, the charge is not easy to overcome the binding force of the fluid and is released to the vicinity of the electrode. Therefore, the viscosity coefficient of fluid motion is inversely proportional to the flow noise. It should be noted that the flow signal voltage induced at this time is applied to the fluid medium as an applied electric field of the dielectric fluid. The higher the flow velocity of the fluid, the higher the signal voltage induced on the electrode, that is, the greater the intensity of the external electric field applied to the dielectric fluid, thereby intensifying the movement of the charge, that is, increasing the flow noise. It is found in practical use that the magnitude of the fluid velocity and the magnitude of the flow noise have an exponential function. In addition, it is known from physics that the frequency of the external electric field has a great influence on the polarization of the dielectric. Since polarization is a process, there is a phenomenon of polarization relaxation in time. When the frequency of the electric field increases, it is too late to turn to polarization (the polarization process of the dielectric composed of polar molecules), that is, the electric dipole is too late to make a corresponding turn with the change of the electric field, so the turning polarization does not actually exist. The dielectric constant will be greatly reduced. Therefore, when the excitation frequency is high, the polarization phenomenon is weakened, and the flow noise is also reduced. However, it should also be noted that excessively high excitation frequencies increase the dielectric loss of the dielectric. Under the action of an applied voltage, a part of the electrical energy in the dielectric is converted into thermal energy. The high-frequency external electric field heats up the dielectric during repeated polarization. The higher the frequency, the more pronounced the heating. Therefore, the excitation frequency generally used for low conductivity measurement flowmeters may be 100 ~ 400Hz.
由于其测量导管内无可动部件或突出于管道内部的部件，因而压力损失很小，可用于测量含有颗粒、悬浮物等液体的流量。 Since the electromagnetic flowmeter has no moving parts or parts protruding from the interior of the pipe, the pressure loss is very small, and it can be used to measure the flow of liquids containing particles, suspended solids, etc. Because the lining and electrodes of the electromagnetic flowmeter are anticorrosive, it can be used to measure fluids of corrosive media. The output potential of the electromagnetic flowmeter has a linear relationship with the flow rate, and is not affected by changes in the physical properties (temperature, pressure, viscosity) of the liquid and the flow state. In addition, it has many advantages such as wide measurement range, fast response, and measurable pulsating flow. Therefore, electromagnetic flowmeters are widely used to measure the flow of fluids such as pulp, black liquor, white liquor, green liquor, lye, acid, sewage, and papermaking additives. However, electromagnetic flowmeters have limitations and deficiencies. If we do not pay attention and take appropriate precautions, we will not be able to accurately measure the flow.