PURPOSE: To automatically detect magnetic abnormality free from the effect of amplitude variation and low frequency drift of a magnetic field measuring signal by automatically changing threshold according to a specified movement means thereof.
CONSTITUTION: A digital magnetic field measuring signal U from an A/D converter 1 undergoes a Hear conversion with a Hear converter section 2 to calculate a Hear spectrum which is applied to a discriminator section 5. This signal U is also applied to a threshold calculating section 4. The calculating section 4 calculates a movement means of amplitude of the signal U during a certain time, square of deviation in the signal U with respect thereto and a movement means of the square of the deviation during a certain time to determine the threshold, which is set for the decision section 5 automatically varying the threshold according to amplitude variation of the signal U and a low frequency drift. This enables automatic detection of magnetic abnormality excellently free from the effect of the amplitude variation and the low frequency drift of the measuring signal.
FUJISAWA TAKASHI
TACHIBANA YASUO
