An Electromagnetic Current Meter

Abstract

We have developed two types of electromagnetic current meters, one employing permanent magnet (P-type) and the other, using electromagnet (E-type). The P-type current meter is easy to operate. It is suitable for the measurements of rapidly varying flows such as orbital wave velocities. However, as the signals are contaminated with polarization potentials of the electrodes, the accuracy of the measurement is limited especially for steady flows. On the other hand, stable and accurate recording of flows is possible with the E-type current meter. Here we get the output of the alternating electromotive force which is amplitude-modulated in proportion to the flow speed. Since the polarization potentials vary slowly with time, only the A.C. components of the current meter output is amplified by the A.C. amplifier. This signal is demodulated and we obtain the final output signal.
The directional response characteristics of the current meter depend on the shape of the meter. We examined several shapes in order to make the directional characteristic curve be of cosine shape.