As is generally known, by detecting a variation in high-frequency loss of material with a high- sensitivity measuring instrument, quality of the material is continuously checked and thus manufacturingprocesses can be controlled. Needless to say, a measuring instrument to be used for this purpose must beinsensitive to any reactance change in the material and stable for long hours continuous operation. Twotypes of meters introduced herein as trail products have a sensitivity of 10 to 30 μA per 10 MΩ to highfrequencyloss, while their sensitivity to capacity variation is less than 1 to 3 μA per 10 pF. Both of thesemeters are most fit for analyzing every kind of material as well as for measuring the thickness of materialand the density of solution. In their application to the measurement of tin and aluminum foils, it wasproved that they successfully detect any deviation in the thickness up to 0.1μ.

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Recently, the problem of detecting and removing tramp metal pieces in ore is becoming greatlyimportant in the mill operation, because these tramp metal pieces sometimes cause serious damage to orecrushing machineries, resulting in unnecessary expense and loss of time for repair. When the tramp metalpiece is magnetic, it is easily removed from ore by the magnetic separation method applying suspendedmagnet. Even though the tramp metal piece is non-agnetic, it is generally detected by the conventionalindustrial metal detector applying the distortion of A. C. magnetic field. When ore itself is magnetic likea magnetite, the above methods have some difficulties to be used for this purpose. Described in this paperto solve such a problem is a mining metal detector which can detect tramp metal pieces in the magneticore by using the difference of specific resistance between ore and metal.

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This paper treats of optimization both of are blending and iron production of a blast furnace. Theprinciple of optimization in regard to blending and production control is developed by use of the basicconcepts of operations research. The optimal set of are blending ratios is attained by the simplex methodof linear programming (L. P.).A control system containing a digital computer executes the calculation ofL. P. and sets the result of the calculation on each controller of the constant-feed-weigher.This systemadjusts the feee ratios to their optimum values applying a matrix method at each period of mixed areanalyzing.Production of pig iron is controlled by the wind control.This system sets the index points oneach of controllers of wind flow, wind temperature and oxygen composition, in conformity with the calculated results on the suit of the mathematical models, which illustrate the dynamic behaviour of ironmelting in the furnace bath. An another part of the system runs always monitering various informationssuch as CO/CO₂ ratio of the top gas and operator's intelligence of coke circulation at the blast nozzles.

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The Hall effect multiplier has a Hall generator which is placed in an air gap of the exciting magneticcircuit. The multiplier output is given as a voltage proportional to the multiplication of Hall current andexciting current. Described in this article are the properties of Hall effect multiplier such as geometry, internal resistance, gain and accuracy of multiplication and temperature variation of output voltage. Themultiplier is in such design as to be applied to watt-onverter, multiplier/divider, square-oot computer, etc. of this multiplier, there are three types, one using the ferrite pot magnetic cores and the other twousing the laminated permalloy cores which are punched in EI shape. Each multiplier has a Hall generatormade of germanium cristal. In this germanium, the antimony is doped in optimum concentration so thatthe best multiplication gain and temperature characteristics are obtained. As an application of this Hall multiplier, the characteristics of watt-onverter is given in appendix.

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