In areas where the use of flow meters is most common in petroleum, chemical, and water resources, the most common ones are ultrasonic flow meters and electromagnetic flow meters. Why are these two types of instruments preferred to be widely used? Let's analyze their main advantages. 1. Wide range of applications. Electromagnetic flowmeter can measure various kinds of acid-alkali liquid, sewage, pulp and other conductive media, non-conductive ultra-pure water, pure water, water and other non-conductive liquid media can be measured with ultrasonic flowmeter, so these two kinds of mutual Almost all common liquids can be measured after bonding.
2. High measurement accuracy. In terms of flow measurement, it can be said that the higher the precision, the better. The two instruments perform very well in terms of accuracy. The conventional accuracy is 1.0, the slightly higher requirement is 0.5, the highest can reach 0.3, or even 0.2, and various flow measurements are currently available. The instrument performs very well.
3. Non-blocking parts without pressure loss. No matter whether it is an electromagnetic flow meter or an ultrasonic flow meter, there are almost no parts inside the draft tube, so there will be no impediment to the medium and there will be no pressure loss. However, the electromagnetic flowmeter may be limited by some extra-high pressure occasions. In this case, an external clamp type ultrasonic flowmeter can be used, and the pressure does not have any influence on the flow measurement.
4. Easy to install. In general, the industrial field measurement of the flow is flanged to connect, inconvenience to damage the existing pipeline can be installed using an external clamp, very convenient.
5. Cost-effective. In addition to demanding ultra-high precision, the prices of these two kinds of instruments are relatively close to the public and acceptable to the general public.
Of course, these two kinds of instruments are not all advantages, some of the inadequacies will also limit its use in a wider range of more areas, such as ultra-high temperature conditions, these two instruments are not performing well. We expect breakthroughs in new materials and new technologies to make them more superior.
Errors caused by various reasons in the application of electromagnetic flowmeters, such as the fluid conductivity, the composition of the fluid, the dirt inside the electromagnetic flowmeter, and the like.
The electromagnetic flowmeter works according to the principle of Faraday's electromagnetic induction law. When a conductor with conductive properties is used to cut magnetic force lines in a magnetic field, an induced electromotive force is generated on the upper and lower sides thereof, and the direction is in accordance with the right-hand rule. Therefore, the application of general electromagnetic flowmeter has certain requirements for the conductivity of the fluid. The application process takes 5us/cm as the boundary.
Electromagnetic flowmeters and ultrasonic flowmeters are velocity flowmeters, all of which are influenced by factors such as: fluid flocculation (fluid is evenly distributed), lining internal scale.
1, the error caused by fluid flocculation:
When the flow velocity of the liquid in the pipeline is axisymmetrically distributed, and in a uniform magnetic field, the magnitude of the electromotive force generated on the flowmeter electrode is independent of the flow velocity distribution of the fluid and is proportional to the average flow velocity of the fluid, otherwise the induction generated by the electrode is induced. The electromotive force is different. Therefore, it is necessary to select an electromagnetic flowmeter in the measuring tube section where the flow velocity of the fluid flow is as small as possible to avoid unnecessary errors.
2. Errors caused by lining scales:
In chemical companies, water treatment companies, and metering meters for daily life, we often see a scale or chemical layer on the inner wall. Do not underestimate this thin layer, which can change the electromotive force deviation of electromagnetic flowmeters. , and then produce zero misalignment. So we often see some sewage treatment plants, in order to improve its measurement accuracy, often cleaning the electrodes inserted into the electromagnetic flowmeter.
At present, electromagnetic flowmeters still dominate the market in fluid metering, energy-saving detection, and other industries. With the increase in electronic chip technology and computer computing efficiency, there has been a trend to replace them with ultrasonic flowmeters.
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