Electromagnetic flow sensors

Abstract

Flow sensors based on the principle of electromagnetic induction were investigated as alternatives to commonly used mechanical devices utilizing rotors and propellers. Prototype sensors were constructed showing considerable promise. Measurement accuracy in excess of 1 cm see-l seems feasible with devices suited to long term battery operation. The inertial effects and many of the reliability problems inherent in moving part devices would be overcome by USC of an electromagnetic sensor. Ocean currents have been routinely mcasured by differences in potential caused by the clcctrically conductive seawater moving through the vertical component of the Earth’s magnetic field (von Arx 1950). Blood flow in animals is also determined by electromagnetic induction, the magnetic field being produced by a coil placed next to the blood vcsscl. The method is also used industrially for monitoring flow in pipes. But the use of a locally generated field has found only occasional application in oceanography (Olson 1972; Tucker 1972; Bowden and Fairbairn 1956). The continually disappointing performance of mechanical current meters has motivated us to take an independent look at the possibilities of electromagnetic flow sensors. Here WC describe first the theory involved in the design of such a sensor. Then we show what results one can get in an actual device. Finally we discuss potential uses, such as current meters, to which this kind of flow sensor can be applied.