The liquid must be a reasonably good conductor of electricity (note: it is okay if the conducting fluid contains some non-conducting solids the conductive fluid surrounding the non-conducting solid matter still provides electrical continuity between the electrodes necessary for induction).This means no special characterization is required to calculate volumetric flow rate.Ī few conditions must be met for this formula to successfully infer volumetric flow rate from induced voltage: Nowhere do we encounter a power, root, or other nonlinear mathematical function in the equation for a magnetic flowmeter. Q = Volumetric flow rate (cubic meters per second) First, we will write the formula relating volumetric flow to average velocity, and then manipulate it to solve for average velocity: We may state the relationship between volumetric flow rate (Q) and motional EMF (ε) more precisely by algebraic substitution. These flow meters are commonly known as magnetic flowmeters or simply magflow meters. Thus, what we have here is a type of flowmeter based on electromagnetic induction. Since we see that this voltage will be proportional to average fluid velocity, it must also be proportional to volumetric flow rate, since volumetric flow rate is also proportional to average fluid velocity. In our example, v is not the velocity of a wire segment, but rather the average velocity of the liquid flow stream (v). V = Velocity of conductor (meters per second)Īssuming a fixed magnetic field strength (constant B) and an electrode spacing equal to the fixed diameter of the pipe (constant l = d), the only variable capable of influencing the magnitude of induced voltage is velocity (v). L = Length of conductor passing through the magnetic field (meters) Metal electrodes opposite each other in the pipe wall intercept this voltage, making it readable to an electronic circuit.Ī voltage induced by the linear motion of a conductor through a magnetic field is called motional EMF, the magnitude of which is predicted by the following formula (assuming perfect perpendicularity between the direction of velocity, the orientation of the magnetic flux lines, and the axis of voltage measurement): The direction of liquid flow cuts perpendicularly through the lines of magnetic flux, generating a voltage along an axis perpendicular to both. Gases must be super-heated into a plasma state before they are able to conduct electricity, and so electromagnetic flow meters cannot be used with most industrial gas flow streams.Ĭonsider water flowing through a pipe, with a magnetic field passing perpendicularly through the pipe: In a practical sense, only liquid flows are measurable using this technique. Therefore, electromagnetic induction is a technique applicable to the measurement of liquid flow rates. However, there is no reason the conductor must be made of copper wire.Īny electrically conductive substance in motion is sufficient to electromagnetically induce a voltage, even if that substance is a liquid. In a generator mechanism, the conductor in question is typically a coil (or set of coils) made of copper wire. This phenomenon is known as electromagnetic induction, and it is the basic principle upon which all electro-mechanical generators operate. When an electrical conductor moves perpendicular to a magnetic field, a voltage is induced in that conductor perpendicular to both the magnetic flux lines and the direction of motion.
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