Pakarab fertilizers limited multan
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| Magnetic Flow meters Magnetic flow meters are very nearly ideal, because they offer no restriction to fluid flow and can meter fluids that other instruments cannot handle. Important metering applications include sludge in sewage-treatment plants, or slurries in mining operations, and liquid metals (liquid sodium) in various industrial processes. When an electrical conductor moves at right angles to a magnetic field, a voltage is induced in the conductor. The voltage induced is proportional to the strength of the magnetic field and the velocity of the conductor. If there is an increase in the intensity of the magnetic field or in the velocity of the conductor, the voltage induced in the conductor also increases. These relationships are in accordance with Faraday’s law of electromagnetic induction. The electrodes penetrate the meter flow tube, make contact with the fluid, and measure the induced voltage across the conductive fluid. The magnitude of induced voltage is proportional to the strength of the magnetic field, or flux, and to the conductor velocity. 71 Field Instrumentation GEN Rev) If the magnetic flux increases, the voltage measured by the electrodes also increases. If the velocity of the fluid moving down the pipe increases, the voltage measured by the electrodes increases. In fact, the induced voltage is linearly proportional to flow velocity—if flow velocity doubles, electrode voltage doubles. Orin general terms E = CV Where, E = voltage Ca constant determined by magnetic field strength, flow tube diameter and other fixed characteristics of the flow meter V = flow velocity. As the electrode voltage changes, the electrical conductivity of the fluid also changes. 72 Field Instrumentation GEN Rev) Conductivity means that an electric current can pass through the fluid. The unit of conductivity is the Siemens, formerly the mho. A Siemens is equivalent to ohm where an ohm is a unit of electrical resistance. (Mho is ohm spelled backwards. Hydrocarbons and non-aqueous (not watery) solutions have little or no conductivity and cannot be metered by magnetic flow meters. Distilled or de- ionized water also may not be conductive enough. Download 3.37 Mb. Share with your friends:
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