Basic Working Principle of Electromagnetic Flowmeter

Electromagnetic flow meters are suitable for measuring liquid-solid two-phase fluids containing solid particles or fibers because their measuring channel is a smooth, straight pipe without obstructions, making them less prone to clogging. They also do not generate pressure loss due to flow measurement; the resistance of the instrument is only the friction loss along the same length of pipe, resulting in significant energy savings. They are particularly suitable for large-diameter water supply pipelines requiring low resistance loss. The volumetric flow rate measured by an electromagnetic flow meter is practically unaffected by changes in fluid density, viscosity, temperature, pressure, and conductivity (as long as these values are above a certain threshold). Compared to most other flow meters, they have lower requirements for the upstream straight pipe section. Electromagnetic flow meters have a wide measurement range, typically 20:1 to 50:1, allowing for a wide selection of flow rates. Their diameter range is wider than other types of flow meters, from a few millimeters to 3 meters. They can measure bidirectional flow and pulsating flow, as long as the pulsation frequency is much lower than the excitation frequency. The instrument output is essentially linear. They offer advantages such as ease of selection of materials for fluid contact components and applicability to corrosive fluids. A significant portion of the flow meters used in our factory are electromagnetic flow meters.

Now I will explain the basic measurement principle of the electromagnetic flowmeter: The measurement principle of the electromagnetic flowmeter is Faraday's principle of electromagnetic induction, that is, when a conductive liquid moves through a magnetic field and cuts magnetic lines of force, an induced electromotive force (EMF) is generated in the conductor. This induced EMF is given by:

E=KBVD

Where: K—instrument constant; B—magnetic induction intensity; V—average flow velocity within the cross-section of the measuring pipe; D—inner diameter of the measuring pipe cross-section. When measuring flow, the conductive liquid flows at a velocity V through a magnetic field perpendicular to the flow direction. The flow of the conductive liquid induces a voltage proportional to the average flow velocity. This induced voltage signal is detected by two or more electrodes in direct contact with the liquid and transmitted via cable to a converter. Through intelligent processing, it is converted into a standard signal of 4~20mA and 0~1kHz for output.