Abstract: The thickness of the layer of remaining molten metal at the bottom of a container is measured on tapping molten metal from the container. An alternating magnetic field is generated with a frequency such that the penetration depth (.delta.) in the metal is of the same order of magnitude as the residue thickness of the melt layer of interest for measurement. The alternating magnetic field is generated such that to begin with field components are reflected at a horizontal surface of the melt layer and towards an alternating magnetic field detection position. When the thickness of the melt layer decreases and approaches the residue thickness, less and less field components will be reflected at the surface of the melt and pass instead through the remaining melt layer. The resulting change in detected alternating magnetic field is utilized, e.g. for triggering an alarm or breaking off tapping in some other way.

Abstract: Parameters of electrically conductive material at high temperature are measured by generating, by means of a transmitter coil, an electromagnetic alternating field which induces currents in the material and by detecting, by means of a receiver coil, a specific component of the secondary electromagnetic alternating field generated by the induced currents and dependent on the measured parameter, the frequency of the generated electromagnetic alternating field being such that the penetration depth of the field into the material is of the same geometrical order of magnitude as the characteristic geometrical dimension of the system, such as the distance between the receiver coil and the material. The specific component of the secondary electromagnetic alternating field is detected by means of a synchronous detector connected to the receiver coil and controlled by a phase-shifted signal from the transmitter.

Abstract: A system for electromagnetically measuring level, distance or flow rate in connection with molten metal contained in a furnace, mould, channel or the like. Separate coreless single or few-turn transmitter and receiver coils are used, the coils being essentially freely positionable relative to the walls of the furnace etc. At least two signal channels are included for signal processing and for producing counteraction between transmitter and/or receiver signals so as to produce a basic measurement signal that is at least substantially balanced with regard to disturbing and unbalance signals, whereby the small variations of the signals induced in the receiver coil or coils due to changes of the level, distance or flow rate of the molten metal can be accurately detected.

Abstract: An arrangement for electro-magnetically measuring level of and/or distance to molten metal contained in a container, particularly a torpedo ladle wagon. Separate transmitter and receiver coils are located displaced relative to each other at or in the container walls so that the molten metal forms an AC magnetic screen between the coils when reaching a predetermined level. Before the molten metal cuts off the alternating magnetic field from the transmitter coil to the receiver coil, the alternating magnetic field sensed by the receiver coil is increased due to alternating magnetic field generated by electric currents induced at the surface of the raising molten metal. The top amplitude of the signal obtained in the receiver coil increases as the wear and erosion of the container lining proceeds.