Nippon Kokan Kabushiki Kaisha

Nippon Kokan K.k.

Yoshihiro Kawase

Seigo Ando

Takeo Yamada

Toshiaki Hosoe

Tomohisa Yamamoto

Eddy current distance measuring apparatus includes a multiplier connected to one secondary coil of a pair of secondary coils in an eddy current sensor. The secondary coil outputs are inputted to a differential amplifier, and the resulting difference is adjusted to be zero when an object the distance to which is to be measured is not present. Thereafter, the sensor is located within measuring distance of, e.g., a steel plate, and the output of the differential amplifier is combined by an amplifier circuit with an oscillator output supplying a current to the primary coil of the sensor. An eddy current distance signal output is thus obtained.

Eddy current distance signal apparatus with temperature change

An apparatus for measuring the level of molten metal in the oscillating mold of a continuous casting machine in operation by an eddy-current type distance measuring device. The oscillation signal component due to the oscillation of the mold is extracted from the output signal of the distance measuring device and the detection sensitivity of the distance measuring device is compensated and controlled so as to maintain the amplitude value of the oscillation signal component at a constant value thereby linearizing the molten metal surface level versus output characteristic.

Apparatus for measuring the level of the molten metal in the mold of a

The distance between the tip of a probe and a high-temperature object of measurement is continuously and accurately measured by arranging the probe comprising a primary coil and a pair of secondary coils substantially vertically to the object of measurement; inducing an AC voltage (e.sub.1) and an AC voltage (e.sub.2) respectively in the pair of secondary coils by means of an AC magnetic field of the primary coil excited by an output voltage (e.sub.out) of a positive feedback amplifier; generating an eddy current in the object of measurement by means of the AC magnetic field of the primary coil to generate another AC magnetic field in the direction opposite to that of the AC magnetic field of the primary coil; impressing an equal DC voltage onto each of the pair of secondary coils to detect respectively a DC voltage (E.sub.1) and a DC voltage (E.sub.2) of the pair of secondary coils; calculating an error voltage (e.sub.4) corresponding to the difference in temperature between the pair of secondary coils, on the basis of the output voltage (e.sub.out) and a value of difference (E.sub.3) between the DC voltages (E.sub.1) and (E.sub.2); and feeding a value of difference (e.sub.3') between the error voltage (e.sub.4) and a value of difference (e.sub.3) between the AC voltages (e.sub.1) and (e.sub.2), back to the positive feedback amplifier, thereby determining the output voltage (e.sub.out) of the positive feedback amplifier, from which the influence of the difference in temperature between the pair of secondary coils has been eliminated.

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Kawasaki, Japan

Yoshihiro Kawase