PURPOSE: To enhance detection accuracy by providing magnetic steel composed of a ferromagnetic substance so as to overlap with a part of a printed circuit board and making it possible to alter the overlap position of magnetic steel and the circuit board or the interval between both of them.
CONSTITUTION: Magnetic steel 7 is provided at a position overlapping with at least a part of a printed circuit board 5 and the pattern of the circuit board 5 at the part overlapping with the magnetic steel 7 is shown in a drawing. That is, the pattern consists of a range 12 where the magnetic field due to a ferromagnetic core 1 crosses and a range 13 where the magnetic field due to the magnetic steel 7 crosses. In this case, by determining the arrangement of a signal pattern 11 and the shape of the magnetic steel 7 so that induced voltage shown by C is generated in the signal pattern 11 crossing the magnetic field 13 due to the magnetic steel 7 when a current having a waveform A is inputted to a coil 4, the induced voltage generated by the magnetic field 12 due to the ferromagnetic core 1 can be negated and accuracy can be enhanced.
NUMAKURA HIROSHI
AKAMATSU KENZO
