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.
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