To solve the problem of smart electromagnetic flowmeter noise, we must first discuss the fluid noise, explore the elements of its attack, find ways to reduce the fluid noise, and improve the signal-to-noise ratio of the sensor, especially for weak excitation current (electromagnetic water meter, two-wire electromagnetic flowmeter It is of great significance to carry out the expansion of the flow measurement at low flow rates (below 0.1 m/s ) and high flow rates ( above 15 m/s ). 　　　　 Fluid noise 　　　　 In addition to the ambient noise, electromagnetic field, electrostatic field, and other factors, the magnetic flowmeter is also a very important factor in the use of electromagnetic flowmeters. Fluid noise is a type of DC polarization voltage, which is particularly prominent in low-frequency square-wave excitation methods, often including: slurry noise, active noise, and high-end flow noise. 　　　　 The elements of fluid noise attack have the following conditions: 　　　　 1. The corrosion resistance of the stainless steel electrode has a very thin passivation layer on its appearance, making the electrochemical reaction reach equilibrium. Solids in the fluid hit the electrodes, causing the electrode surface passivation layer to be damaged and lose electrochemical balance. The touch of metal materials with fluid media has the ability to regenerate from scratch to create an electrochemically balanced surface passivation layer. At the time of electrochemical equilibrium, free ions in the metal and fluid continuously undergo electrochemical reactions under the effect of the signal electric field. Solid particles collide with the electrode and continuously damage the maintained passivation layer; the electrochemical reaction also repeats the formation of a passivation layer, so that the potential between the electrodes changes continuously and fluctuates, and this changed potential constitutes the fluid noise in the flow signal. This condition is also known as slurry noise in electromagnetic flowmeters. The theory and practice indicate that the increase in the frequency of changes in the electric field that affect the electro-reaction signal will make the noise fluctuations in the fluid agile. This is the factor that the high frequency excitation and dual frequency excitation can solve the measurement of the slurry.  　　 　　    2. The fluid rubs the fabric and the electrode. The positive and negative ions in the fluid separate from the electrolyte fluid. The rougher the fabric and electrode appearance, the higher the free ion concentration. By the effect of the electrode signal electric field, a certain other ion will move to the electrode and constitute a noise voltage. Such noise is called active noise. Activity noise is superior when measured at low conductivity. The activity noise is related to the strength of the external electric field. The higher the inductive signal at high flow rates, the greater the noise fluctuations and the unstable output.  　　 　　 3. The drastic changes in fluid conductivity and pH will also constitute active noise. The measurement instability in the upstream of the flow meter is a typical example. The elements are different when the medium is not evenly mixed. In the fluid, positive ions and negative ions are simply separated from each other. The effect of the signal electric field on the electrodes is that one part of the ions moves toward the electrode, which constitutes an active noise voltage and constitutes an unstable output.  　　 　　    4. As the thickness of the laminar boundary layer near the surface of the fabric and electrode at the high flow velocity of the active fluid becomes very thin, as shown in Figure 3 , the roughness of the fabric and the electrode highly breaks through the thickness of the laminar flow boundary layer, and the fluid hits this Some roughness heights, divergence and sudden changes in the onset of flow. There is a flow velocity weight that is somewhat the same as (or opposite to) the center axis of the measuring tube. Due to the effect of the signal weight function, the electrode signal has a large impact and constitutes a large positive error, which is the high-end flow noise.  　　 　　 Obviously, the active noise and the high-end flow noise in the above-mentioned fluid noise are directly related to the fabric surface roughness of the measuring tube and the surface roughness of the electrode, and the serous noise of the polarization voltage attack is also closely related to the surface roughness of the electrode. Jiangsu Wanjie Instrument Technology Co., Ltd. Recommends for You: Smart Electromagnetic Flowmeter
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