Large-diameter instruments are widely used in water supply and drainage projects, such as flow monitoring of main pipelines in urban tap water supply systems and sewage discharge metering in sewage treatment plants. Their large-diameter design can adapt to high flow requirements and ensure accurate metering in large-scale fluid transportation. Small and medium diameter electromagnetic flowmeters are commonly used for difficult-to-measure fluids such as solid-liquid two-phase flowmeters or in demanding applications. For example, they are used to measure the flow of pulp and black liquor in the paper industry, where these fluids contain a large amount of fiber and impurities, making them difficult to accurately measure with traditional flowmeters. Electromagnetic flowmeters, with their excellent adaptability to conductive liquids, are an ideal choice. In the non-ferrous metallurgical industry, precise flow control is required for slurry transportation to ensure production efficiency; electromagnetic flowmeters can effectively handle the high concentration and abrasive characteristics of slurries. In coal preparation plants, electromagnetic flowmeters can monitor flow in real time during coal slurry transportation, optimizing the coal washing process. In the chemical industry, the lining material of electromagnetic flowmeters is chosen to provide excellent corrosion resistance for highly corrosive acid and alkali solutions, ensuring long-term stable operation. In the steel industry, electromagnetic flowmeters can accurately monitor cooling water flow and promptly detect leaks in blast furnace tuyeres cooling water control and leak detection, ensuring the safe operation of the blast furnace. In long-distance hydraulic coal pipeline transportation, electromagnetic flowmeters are used for flow measurement and control, ensuring the continuity and accuracy of coal transportation. Small-diameter and micro-diameter electromagnetic flowmeters are commonly used in hygiene-critical environments such as the pharmaceutical, food, and bioengineering industries. Examples include drug delivery and metering in pharmaceutical processes, raw material ratio control in beverage production lines, and culture medium flow monitoring in bioreactors. The unobstructed flow design and easy-to-clean characteristics of electromagnetic flowmeters meet stringent hygiene standards and cleanliness requirements. Electromagnetic flowmeters can be used for metering in all these applications.
Electromagnetic flowmeters can be selected based on the following six key points:
1. Accuracy Class and Functions: Depending on the application requirements, an appropriate accuracy class must be selected. Generally, industrial applications use accuracy classes of 0.5, 1, or 2. Higher accuracy is required for demanding applications such as trade settlement. Functionally, options include bidirectional flow measurement, total quantity calculation, over-range alarm, power failure protection, and remote data transmission (such as 4-20mA signal output, HART protocol, Modbus protocol, etc.) to meet the needs of automated control systems.
2. Flow velocity, full-scale flow rate, rangeability, and pipe diameter: The selection of flow velocity should be based on the pipe diameter and flow rate. A flow velocity range of 0.5-8 m/s is generally recommended. Too low a velocity can lead to sedimentation, while too high a velocity may generate eddies, affecting measurement accuracy. The full-scale flow rate should be set at approximately 70%-80% of the commonly used flow rate to ensure linearity and stability. Rangeability refers to the ratio of the maximum to the minimum flow rate that the instrument can measure. Electromagnetic flowmeters typically have a rangeability of 1:20 to 1:100; when selecting a flowmeter, ensure that the actual flow rate falls within this range. The pipe diameter must be matched to the pipe diameter, or connected using reducing fittings, to ensure sufficient fluid development within the pipe and reduce eddy current interference.
3. Liquid conductivity: The working principle of an electromagnetic flowmeter is based on Faraday's law of electromagnetic induction, requiring the measured liquid to have a certain conductivity, generally greater than 5 μS/cm. For pure water with low conductivity, a specially designed electromagnetic flowmeter or the addition of electrolyte is required. If the liquid conductivity is too low, the signal will be weak, increasing measurement error.
4. Impurities in the Liquid: The presence of impurities such as air bubbles, solid particles, or fibers in the liquid may affect measurement accuracy. Air bubbles can cause electrode short circuits, generating false signals; solid particles may wear down the electrodes or adhere to the electrode surface, altering the electrode circuit resistance; fibrous materials may become entangled on the electrodes, affecting signal transmission. Therefore, the type, concentration, and form of impurities must be considered when selecting a model. Pretreatment measures (such as installing filters or deaerators) or selecting a model with strong anti-interference capabilities may be necessary.
5. Adhesion and Sedimentation: When measuring liquids that are prone to sedimentation or adhesion (such as certain chemical solutions and slurries), a layer of deposit may adhere to the electrode surface, causing changes in electrode circuit resistance and leading to measurement errors. To solve this problem, an electromagnetic flowmeter with a scraper electrode and online cleaning capability can be selected, or a lining material such as PTFE (polytetrafluoroethylene) that is not prone to adhesion can be used, with regular cleaning and maintenance to ensure measurement accuracy.
6. Selection of materials for components in contact with fluids: The materials for components in contact with fluids (such as electrodes, linings, flange seals, etc.) should be selected based on the corrosiveness, temperature, pressure, and other characteristics of the liquid being tested. For high-temperature media, high-temperature resistant lining and electrode materials should be selected. For applications with high hygiene requirements, materials such as 316L stainless steel can be used to ensure material safety and compatibility.
