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Hi, long time no see! Your industrial control assistant is back. Do you know about electromagnetic flowmeters? They are a new type of flow measurement instrument that developed rapidly in the 1950s and 1960s along with the advancement of electronic technology. So do you know how it works? Today we’re going to take a look at the principles that underpin its remarkable role in industry. Working principle of electromagnetic flowmeters: Electromagnetic flowmeters are designed based on Faraday’s law of electromagnetic induction; they are instruments used to measure the volumetric flow rate of conductive liquids in meters. Due to its unique advantages, electromagnetic flowmeters are now widely used in the measurement of the flow rate of various conductive liquids in industrial processes, such as corrosive media like acids, alkalis, and salts. They are also employed for measuring the flow rate of various slurries, thus establishing a distinct field of application for this type of flowmeter. Structurally, an electromagnetic flowmeter consists of an electromagnetic flow sensor and a converter. The sensor is installed on industrial process pipelines; its function is to linearly convert the volumetric flow rate of the liquid flowing into the pipeline into an induced potential signal, which is then sent to the converter via a transmission line. The converter is installed not too far away from the sensor; it amplifies the flow signal sent by the sensor and converts it into a standard electrical signal that is proportional to the flow rate, so that it can be displayed, accumulated, and used for control purposes. The measurement principle of electromagnetic flowmeters is based on Faraday’s law of electromagnetic induction. When a conductor moves in a magnetic field and cuts through the magnetic flux lines, an induced electromotive force e is generated at both ends of the conductor. The direction of this force is determined by the right-hand rule, while its magnitude is proportional to the magnetic flux density B, the length L of the conductor within the magnetic field, and the speed u at which the conductor moves. If B, L, and u are perpendicular to each other, then e = Blu. Similarly, in a uniform magnetic field with magnetic induction strength B, a non-magnetic pipe with an inner diameter of D is placed perpendicular to the direction of the magnetic field. When a conductive fluid flows through this pipe at a velocity of u, the conductive fluid cuts through the magnetic field lines. If counter-electrodes are installed at the two ends of a diameter in the pipe cross-section that is perpendicular to the magnetic field, it can be shown that as long as the flow velocity distribution within the pipe is axially symmetric, an induced electromotive force is generated between the two electrodes: e = BD. Here, u represents the average flow velocity in the pipe cross-section. The volumetric flow rate through the pipe can then be calculated as: qv = rDU”. As can be seen from this equation, the volumetric flow rate qv is linearly related to the induced electromotive force e and the inner diameter D of the pipe; it is inversely proportional to the magnetic flux density B of the magnetic field, and it is independent of other physical parameters. This is the measurement principle of electromagnetic flowmeters. It should be noted that for the equation qv=πDU~ to hold strictly, the measurement conditions must satisfy the following assumptions: ① The magnetic field is a uniformly distributed constant magnetic field; ② The flow velocity of the fluid being measured is axially symmetric; ③ The liquid being measured is non-magnetic; ④ The electrical conductivity of the liquid being measured is uniform, i.e., isotropic. Power supply methods for electromagnetic flowmeters: Electromagnetic flowmeters rely on an electric power supply to function. Depending on the different operating conditions, there are currently three main ways of supplying power to these flowmeters: supply from 220V AC mains electricity, supply from 22V DC power, and supply from batteries (primarily high-performance lithium batteries). 1. For 220V power supply, electromagnetic flowmeters are widely used at present. Industrial sites usually have 220V power supply; as long as the flowmeter is installed according to the specifications, no additional equipment is required, and it can start operating once powered on. 220V distribution electromagnetic flowmeters can be manufactured as integrated units or in a split design. II. The 22V-powered electromagnetic flowmeter is suitable for industrial sites where the use of alternating current is not permitted, or where low-voltage direct current is preferred for safety reasons. In cases where a flow accumulation meter is used to supply power to the electromagnetic flowmeter, only a 22V battery power source can be employed. These electromagnetic flowmeters are not widely used at present; they are mainly applied in situations where there is no power supply available on site. In addition, it also has functions for detecting common faults, setting and alerting for upstream and downstream flow rates, switching between forward and reverse flow directions, as well as 485 communication capabilities. In addition to having various power distribution methods, electromagnetic flowmeters also possess strong functional capabilities; they can be used to measure the flow rate of liquid substances, as well as the forward and reverse flow rates, and they are capable of determining both instantaneous flow rates and cumulative flow volumes. It can be made in either integrated or separate types, depending on the customer’s specifications. III. Battery power distribution is used in situations where there is no external power source available on site, or for safety reasons; it allows for the display of instantaneous flow rates and cumulative flow amounts on-site, thereby eliminating the need to connect to an external power source. This type of battery power distribution is particularly important in remote areas. The main drawback is the need to regularly inspect and replace the batteries. That’s all for today’s content. If there’s anything else you’d like to know or discuss, feel free to leave a message. Updates will be provided regularly, so please stay tuned.