Electromagnetic flowmeter

An electromagnetic flowmeter comprising:

• A. a cylindrical flow tube through which the fluid to be metered is conducted, said tube being formed of non-magnetizable metal whose interior is lined by an electrically-insulating material;
• B. a pair of electrodes disposed at diametrically-opposed positions on said tube;
• and
• C. means to establish a transverse magnetic field in said tube which is intercepted by the fluid conducted therethrough to induce a voltage therein which is transferred to said electrodes to yield a signal indicative of flow rate, said means including at least one core of solid ferromagnetic material surrounded by a coil to which a low-frequency excitation current is applied, said core having a front face conforming to the periphery of the tube and having a cavity therein which lies in the central region thereof in which the intensity of the magnetic field is relatively weak due to skin effects, whereby the intensity of the field produced thereby is essentially unaffected by the cavity, whereas the mass of the core is substantially reduced.