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The corrosion resistance of the measuring medium determines the choice of electrode material for electromagnetic flowmeters; at the same time, it is necessary that the electrodes do not exhibit surface effects. In other words, the corrosion resistance of the electrode is an important factor in selecting the material; however, even though an electrode material may have excellent corrosion resistance against the medium being tested, it is not necessarily the suitable material – it is also necessary to consider whether electrode surface effects will occur. The electrodes require extremely high corrosion resistance; corrosion is not allowed at all, yet even very low levels of corrosion can still occur in practical engineering applications. Corrosion can damage the seal between the electrode and the fabric, leading to a leakage of the medium. In mild cases, this damages the insulation and renders the instrument unusable; in severe cases, it can destroy the entire flow sensor. The data presented in various documents are mostly obtained under laboratory conditions, whereas fluids used in practice often contain trace impurities or even mixtures of various impurities; their corrosivity differs significantly from that of pure substances. Therefore, when it is used in important occasions, it is necessary to conduct corrosion tests on site. The surface effects of electrodes are divided into three aspects: surface chemical reactions, electrochemical and polarization phenomena, and the catalytic action of electrodes. Surface chemical reactions, such as those that occur when an electrode comes into contact with a medium, result in the formation of an oxide layer or passivation film, which increases the surface contact resistance; in some cases, an insulating layer is even formed (for example, tantalum oxidizes to form an insulating layer). The perturbing potential generated by the electrochemical process causes the electrolyte to develop different polarities on the surfaces of the two electrodes, resulting in polarization. Random noise resulting from changes in electrochemical potential causes fluctuations in the output signal; sometimes, sudden changes in electrochemical potential lead to spike pulses in the output signal. The medium under test undergoes a chemical reaction under the catalytic action of the electrodes. For example, platinum electrode electromagnetic flowmeters generate mist on the surface of the electrodes when measuring hydrogen peroxide, and an unstable output signal is also produced even when the flow rate is zero. In electromagnetic flowmeters installed in plastic pipes or metal pipes with insulating linings, grounding rings need to be installed at both ends of the sensor; their corrosion resistance requirement is lower than that of the electrodes, and they should be replaced regularly if corrosion occurs. If the conductivity of the medium being tested is low, a metal short tube can be used in place of the grounding ring to ensure proper grounding