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1. The fluid friction lining and electrodes of the sewage flow meter separate positive and negative ions generated in the fluid from the electrolyte fluid. The rougher the lining and electrode surfaces, the higher the concentration of free ions. Under the influence of the electric field generated by the electrode signal, some ions move toward the electrode, resulting in noise voltage; this type of noise is known as drift noise. Flow noise is more prominent during low conductivity measurements. Flow noise is related to the external electric field strength; at higher flow rates, the induced signal becomes greater, and so does the noise level, resulting in unstable output. 2. The corrosion resistance of stainless steel electrodes is due to a very thin passivation layer on their surface, which brings the electrochemical reaction to an equilibrium state. Solid particles in the fluid strike the electrodes, destroying the passivation layer on their surfaces and disrupting the electrochemical equilibrium. When metal materials come into contact with fluid media, they have the ability to regenerate a surface passivation layer in order to maintain electrochemical equilibrium. During the establishment of electrochemical equilibrium, free ions in the metal and the fluid continuously undergo electrochemical reactions under the influence of the signal electric field. Solid particles strike the electrode, continuously destroying the protective passivation layer ； The electrochemical reaction repeatedly forms a passivation layer, resulting in significant fluctuations in the potential between the electrodes. These changing potentials cause fluid noise in the flow signal. This condition is what is commonly referred to as slurry noise in electromagnetic flowmeters. Theory and practice show that increasing the frequency of the electric field changes affecting electrochemical reaction signals can rapidly reduce the amplitude of fluid noise; this is why high-frequency excitation and dual-frequency excitation can be used to address slurry measurement issues. 3. Due to the high flow velocity, the thickness of the laminar boundary layer near the lining and electrodes becomes very thin; the roughness of the lining and electrodes exceeds the thickness of this laminar boundary layer. When the fluid strikes this rough surface, the flow velocity diverges and changes abruptly. There are flow velocity components that are in the same direction (or opposite direction) as the central axis of the measurement tube; due to the effect of the signal weighting function, these components have a significant impact on the electrode signals, resulting in large positive errors. This is what constitutes high-frequency flow velocity noise. 4. Sudden changes in fluid conductivity and pH value can also generate flow noise; unstable measurements resulting from the addition of chemicals upstream of the flow meter are a typical example of this. The reason is that when different media are mixed unevenly, positive and negative ions tend to separate in the fluid; under the influence of the electric field generated by the electrode signals, some of these ions move toward the electrodes, resulting in flow noise voltage and causing instability in the output. It can be seen that the flow noise and high-speed flow noise in the fluid noise of the aforementioned sewage flow meter are directly related to the roughness of the lining and electrode surfaces of the measurement tube, while the slurry noise generated by the polarization voltage is also highly dependent on the roughness of the electrode surfaces.