If a conductive substance with a higher electrical conductivity than the liquid is attached, measure the fluid that is liable to adhere to and deposit the substance on the tube wall. The signal potential will be short-circuited and unable to work. If it is a non-conductive layer, it should first pay attention to the pollution of the electrode. Scraper-type electrodes can be used to manually scrape out dirt regularly outside the sensor. Foreign products used to have ultrasonic transducers on the electrodes to remove surface dirt layers, but these are now rare. There is also a temporary disconnection of the measurement circuit, a low voltage and large current flows during the electrode discontinuity, and the oil and grease adhesion layer is removed by incineration. Places that are prone to adhesion can increase the flow rate to achieve the purpose of self-cleaning. A more convenient and easy-to-clean pipe connection can also be adopted, and the cleaning sensor can be omitted. The instrument can still work, non-contact electrode electromagnetic flowmeter is attached with non-conductive film layer. However, if it is a highly conductive layer, it will not work.
与流体接触零部件材料的选择 Selection of materials for electromagnetic flowmeter and fluid contact parts
The material's corrosion resistance, wear resistance, and upper temperature limit affect the adaptability of the instrument to fluids. Because there are few parts, sensor parts that come in contact with fluid have lining (or measuring tube made of insulating material) electrodes, grounding rings, and gaskets. Simple shape, flexible data selection, strong adaptability of electromagnetic flow sensor to fluid.
1 lining information of electromagnetic flowmeter (or measuring tube directly in contact with the medium)
Such as industrial water, waste water and weak acids and bases, commonly used lining materials are fluoroplastic polyurethane rubber, neoprene and ceramics. In recent years, high-purity alumina 99.99% A I2O3 ceramics have been used for lining, but only for small and medium-caliber sensors. Neoprene and FRP are used for non-corrosive or weakly corrosive liquids. The lowest price.
的电极和接地环材料 2 Electromagnetic flowmeter electrode and ground ring material
Secondly, consider whether surface effects such as passivation and the resulting noise will occur. The resistance of the electrode to the measurement medium is the first factor to consider when selecting data.
① Select corrosion-resistant materials
Common metal materials include molybdenum-containing acid-resistant steel 1Cr18Ni12Mo2Ti Hastelloy (corrosion-resistant nickel-based alloy) BC titanium, tantalum, platinum iridium alloy, electromagnetic flowmeter electrodes have high corrosion resistance requirements. Covers almost all chemical fluids. In addition, there are low-noise electrodes suitable for slurry, conductive rubber electrodes, conductive fluoroplastic electrodes and porous ceramic electrodes, or metal electrodes coated with these materials. In principle, the choice of electrode material should be determined from the user's actual application or previous experience of the medium in other equipment. Sometimes necessary experiments are performed, such as taking liquid samples on site for corrosiveness tests of materials to be used in the laboratory. The best experiment is to hang on the spot. This is the corrosiveness test that is closest to the actual application conditions. It can be compared to be reliable. Conclusion.
②Prevent electrode surface effects
However, sometimes the electrode material has good corrosion resistance to the measured medium, and the corrosion resistance of the electrode is an important factor in selecting data. It is not necessarily the applicable information, and it is necessary to prevent the occurrence of electrode surface effects. Electrode surface effects are divided into three aspects: surface chemical reactions, electrochemical and polarization phenomena, and the catalytic effect of electrodes. Form a passivation film or oxide layer. It may play an active role in maintaining the corrosion resistance. Chemical reaction effects such as the contact between the electrode surface and the measured medium. But it is also possible to increase surface contact resistance. For example, tantalum is oxidized in contact with water, forming an insulating layer. Regarding the medium that prevents or mitigates the effect of the electrode surface—electrode material matching, there is not as much information available as corrosivity, and there are only some limited experiences that have yet to be accumulated in practice. The corrosion resistance is lower than that of the electrode. The grounding ring is connected to the two ends of the flow sensor of the plastic pipe or the metal pipe lined with insulation. 选用耐酸钢或哈氏合金。 Usually electromagnetic flowmeters use acid-resistant steel or Hastelloy. Because of its large size, economically, no precious metals such as tantalum and platinum are used. If the metal process pipe is in direct contact with the fluid, a ground ring is not required.