ANORDNING VID ELEKTRISKA INDUKTIONSUGNAR

1466217 Liquid level detector AEGELOTHERM GmbH 22 May 1975 [31 May 1974] 22364/75 Heading G1N An electrical induction furnace for heating liquid electrically conducting materials comprises a crucible 1 surrounded in the region of the melt 3 by a plurality of turns of an induction heating coil 2 connected to a source of A.C. 4 and a liquid level sensing device including indicating means responsive to a change in electrical potential between turns of the induction coil. Thus a pair of adjacent turns is connected across the primary of a transformer 20 via e.g. taps 21, 211, the transformer secondary winding connecting via rectifier 21 to resistor 22. A direct current proportional to the alternating current in the coil 2 is obtained by current transformer 14, and rectifier 15, producing a corresponding voltage across resistor 16. The voltages across resistors 16, 22 are compared in a circuit containing resistors 23, 24, If they are unequal, the difference voltage at the output of amplifier 26 causes an indication from luminous diode e.g. 27, which indicates a change in coil impedence due to melt entering the space between the respective pair of turns.