Patent ID: 9709920
Date: 2017-07-18
CPC Classifications: G03G

Claim:
1. A sensor comprising: an oscillation circuit including a resonance circuit having a coil; a differential transformer including the coil as a primary coil, the differential transformer further including a secondary coil and a movable iron core; and an amplification portion for amplifying a signal output from the secondary coil, wherein the differential transformer is configured such that, the primary coil is composed of a first coil, and the secondary coil is composed of a reference coil and a detection coil, the coils all being three-dimensional coils, the movable iron core is moved toward the reference coil, and an electromotive voltage generated in the reference coil is made higher than an electromotive voltage generated in the detection coil, and as an amount or density of magnetic substance as a detection target decreases, the signal output from the secondary coil increases, and as the amount or density of magnetic substance increases, the signal decreases, the amplification portion has, as frequency characteristics thereof, a frequency band such that, as a frequency of the signal decreases, an amplification factor of the signal decreases, and as the frequency of the signal increases, the amplification factor of the signal increases, and a resonance frequency of the resonance circuit falls within the frequency band.