Abstract: An electromagnetic flowmeter in which the fluid whose flow rate is to be measured is conducted through the flow tube of a primary provided with a pair of diametrically-opposed electrodes to intercept a magnetic field established by an electromagnet whose coil is excited by a current having a rectangular waveform whose frequency is low relative to that of a commercial a-c power line. The electrodes of the primary are connected through a transmission line to the input amplifiers of a secondary, the transmission line being constituted by a pair of shielded cables each including an inner line connecting an electrode to the input of a respective amplifier and an outer shield connected to the output of the amplifier, the cables being surrounded by a common outer shield.

Abstract: A technique for exciting the electromagnet of a magnetic flowmeter in which a fluid to be metered is conducted through a flow tube having detecting electrodes, the fluid intercepting a magnetic field established by the electromagnet to induce a signal in the electrodes indicative of flow in a high flow-rate range as well as in a low flow-rate range. In this technique, derived from the electrode signal is a control signal whose frequency is a function of the velocity of the fluid passing through the tube, the excitation current supplied to the electromagnet being governed by the control signal so that it has a frequency which is higher in the high flow-rate range and lower in the low flow-rate range.