Abstract: A method and apparatus for measuring the spacing between a pair of surfaces, at least one of which is of electrically conductive and/or ferromagnetic material, so that the wear of one of the surfaces can be determined. A measuring transducer having a core with coils, and a reference transducer substantially identical to the measuring transducer, are the basic elements. The measuring transducer is mounted close to an opposing surface of conductive and/or ferromagnetic material with a gap between them, and the reference transducer is mounted with a constant gap spacing between it and a reference surface of the same material as the opposing surface.

Abstract: A centrifugal pump having an impeller rotatable about an axis of rotation at its center has its operation controlled so as to regulate the size of a gas bubble. When pumping a liquid or suspension (such as paper pulp with a consistency of about 8-15 percent) which contains gas, the gas has a tendency to collect adjacent the impeller center, and impede operation of the pump. Using a number of electrodes which extend into operative association with the chamber of the pump in which the gas bubble tends to collect, and by taking advantage of the differences in electrical conductivity of the gas as compared to the liquid or suspension being pumped, the size of the gas bubble may be determined. When the size is too large, gas is automatically discharged from the pump.