Abstract: Metal detection apparatus comprises an oscillator circuit including an inductive detection coil and a detector for rectifying the output of the oscillator circuit synchronously with the frequency of oscillation. A comparison circuit compares the rectified output of the oscillator circuit with a reference signal and generates an output signal having a value related to the amplitude of the oscillator output. A feedback circuit generates a positive feedback signal and applies it to the oscillator circuit to maintain its oscillation at a predetermined amplitude under quiescent conditions. The circuit is largely immune to electromagnetic interference and temperature sensitive effects.

Abstract: Described is a cathode assembly for an electrolytic cell for the production of metal, e.g., aluminum, by electrolysis of molten electrolyte containing a compound of the metal, e.g., alumina. The cathode assembly comprises pedestals, e.g., a carbon pedestal, disposed on the cell floor beneath the shadow of the anode of the cell. The pedestal rises from the cell floor to a height of at least the highest interface of the metal pad and molten electrolyte that exists during cell operation. Embedded in the pedestal is at least one refractory hard metal element, e.g., titanium diboride, which is embedded to a depth of at least about 75 percent of its length. The refractory hard metal element(s) can be flush with the top surface of the pedestal; but, preferably protrude slightly from the top surface of the pedestal. The refractory hard metal element can be a solid or hollow body, e.g., cylinder.