To improve speed and accuracy for controlling a liquid metal surface level by performing processing to compensate a temperature of a detection coil and influence from disturbance and also performing wave detection at high speed with high accuracy.
Two detection secondary coils 22A, 22B are used to magnetically shield an upper detection coil so that a change in the lever of a liquid metal surface 24 functions only to a lower coil, thereby preventing detection balance between the coils 22A, 22B from being disturbed by influence of other disturbance. In addition, a sufficiently large fixed resistor is connected in series with the coils 22A, 22B and a thermosensitive magnetic material is placed in the vicinity of the coils 22A, 22B, wherein when a peripheral temperature varies, a change in temperature of the fixed resistor is small even if coil resistance of an excitation primary coil 21 and the coils 22A, 22B changes. Thus a rate of change in resistance of the addition result is small, so that influence of the change in temperature is small while magnetic flux density in the vicinity of the coils 22A, 22B is stable by the thermosensitive magnetic material.
MIKI MASAYUKI
TODA SEIJI
