The basic working principle of electromagnetic flowmeters
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Electromagnetic flowmeters are suitable for measuring liquid-solid two-phase fluids containing solid particles or fibers, as their measurement channel consists of a smooth straight tube without any flow-obstructing elements, making clogging less likely； At the same time, it does not cause pressure losses resulting from flow measurement; the resistance of the instrument is merely that of a pipe of the same length, resulting in significant energy savings. It is thus most suitable for large-diameter water supply pipes where low resistance losses are required ； The volumetric flow rate measured by an electromagnetic flowmeter is, in fact, not significantly affected by changes in fluid density, viscosity, temperature, pressure, and conductivity (as long as they are above a certain threshold) ； Compared to most other flow meters, the required straight pipe section in front is lower ； Electromagnetic flowmeters have a large measurement range, typically 20:1 to 50:1, offering a wide selectable flow range ； The diameter range of electromagnetic flowmeters is wider than that of other types of flow meters, ranging from a few millimeters to 3 meters ； It can measure flow in both forward and reverse directions, as well as pulsating flow, provided that the pulsation frequency is much lower than the excitation frequency ； The instrument output is essentially linear ； It is easy to select the material types for fluid contacts, and it can be used with corrosive fluids among other advantages. A considerable portion of the flow meters used in our factory are electromagnetic flow meters. http://news.upc.edu.cn/Uploads/2006/2006115113857141.jpg Now I will explain to you the basic measurement principle of electromagnetic flowmeters: The measurement principle of electromagnetic flowmeters is based on Faraday’s law of electromagnetic induction; that is, when a conductive fluid moves through a magnetic field, cutting across the magnetic field lines, an induced electromotive force is generated in the conductor. This induced electromotive force E is given by the formula E=KBVD, where K is the instrument constant ； B——Magnetic flux density ； V —— Average flow velocity within the pipe cross-section ； D — The inner diameter of the pipe cross-section. When measuring flow rate, a conductive liquid flows at a velocity V through a magnetic field perpendicular to the direction of flow. The flow of this conductive liquid generates a voltage proportional to its average flow velocity; this induced voltage signal is detected by two or more electrodes in direct contact with the liquid, and is transmitted via cables to a converter where it is processed intelligently to be converted into standard signals of 4–20 mA and 0–1 kHz. Electromagnetic flowmeters are suitable for measuring liquid-solid two-phase fluids containing solid particles or fibers, as their measurement channel consists of a smooth straight tube without any flow-obstructing elements, making clogging less likely ； At the same time, it does not cause pressure losses resulting from flow measurement; the resistance of the instrument is merely that of a pipe of the same length, resulting in significant energy savings. It is thus most suitable for large-diameter water supply pipes where low resistance losses are required ； The volumetric flow rate measured by an electromagnetic flowmeter is, in fact, not significantly affected by changes in fluid density, viscosity, temperature, pressure, and conductivity (as long as they are above a certain threshold) ； Compared to most other flow meters, the required straight pipe section in front is lower ； Electromagnetic flowmeters have a large measurement range, typically 20:1 to 50:1, offering a wide selectable flow range ； The diameter range of electromagnetic flowmeters is wider than that of other types of flow meters, ranging from a few millimeters to 3 meters ； It can measure flow in both forward and reverse directions, as well as pulsating flow, provided that the pulsation frequency is much lower than the excitation frequency ； The instrument output is essentially linear ； It is easy to select the material types for fluid contacts, and it can be used with corrosive fluids among other advantages. A considerable portion of the flow meters used in our factory are electromagnetic flow meters. Now I will explain to you the basic measurement principle of electromagnetic flowmeters: The measurement principle of electromagnetic flowmeters is based on Faraday’s law of electromagnetic induction; that is, when a conductive fluid moves through a magnetic field, cutting across the magnetic field lines, an induced electromotive force is generated in the conductor. This induced electromotive force E is given by the formula E=KBVD, where K is the instrument constant ； B——Magnetic flux density ； V —— Average flow velocity within the pipe cross-section ； D — The inner diameter of the pipe cross-section. When measuring flow rate, a conductive liquid flows at a velocity V through a magnetic field perpendicular to the direction of flow. The flow of this conductive liquid generates a voltage proportional to its average flow velocity; this induced voltage signal is detected by two or more electrodes in direct contact with the liquid, and is transmitted via cables to a converter where it is processed intelligently to be converted into standard signals of 4–20 mA and 0–1 kHz.
The layout might give a better result!
I’ve learned it.* http://www.shakic.com/cp/jianci.HTM
This post was last edited by qugd on 2010-11-28 at 22:52. Could the original poster explain the detection mechanism and applications of the excitation method for communication? Faraday’s principle of electromagnetic induction is based on the properties of direct current; approximately half of electromagnetic flowmeters use alternating current for excitation. So, what are the differences and characteristics in their detection mechanism compared to those using direct current excitation?
I spent a long time trying to understand it but couldn’t; it’s better to just read the control manual directly.
Brother on the 4th floor, the only advantage of AC excitation is that it prevents polarization of the electrodes, as is the case with DC excitation. However, its disadvantages include the occurrence of orthogonal interference, in-phase interference, and zero-point drift; gradually, it may be replaced by low-frequency square-wave excitation.
Electromagnetic flowmeter failure: What does “tol coil curr” mean?
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I would like to ask the experts in instrumentation: if a thick layer of scale forms on the inner surface of an electromagnetic flowmeter, what changes will occur in its output?