JPS6418087A - Electromagnetic induction detector - Google Patents

Abstract

PURPOSE:To obtain a detector which is kept low in measuring errors when impulse noise is mixed in without increasing exciting current by providing a rate-of-change limiter on the fore part of a BPF and varying limiting value by means of a phase of an exciting signal from an exciting circuit. CONSTITUTION:An exciting coil 11 is driven by alternating current signals by the use of an exciting circuit 14 and a magnetic flux 13 is generated. A detecting coil 12 detects the magnetic fluxes 13 and electromotive force is generated across it. The electromotive force is amplified by a fore amplifier 15 and input in a rate-of-change limiter 20. The rate-of-change limiter 20 varies limiting value of the rate-of-change by means of a limiting value control signal 24 obtained from the exciting circuit 14, the output 22 is converted into a direct current signal by an AC/DC converter 17 and output from an operation output circuit 18 after the output 22 is passed through a BPF 16 which passes exciting alternating current signal frequency. Therefore, noise is not transmitted to the rate-of-change limiter 20 and excessive measuring errors are prevented from occurring because large signal rate-of-change of the noise exceeds the rate-of-change allowed for the rate-of-change limiter 20 even if the excessive impulse noise is mixed in to electromotive force inducted in a detecting circuit.