MAGNETIC FLUX DETECTION COIL

PURPOSE:To enhance noise removing capacity by allowing the impedances of loops to coincide, by providing an inductance fine adjustment pad having a photomagnetic effect in each loop and selectively irradiating said pad with light. CONSTITUTION:When three coordinates axes X, Y, Z are determined, because loops 1, 2 are connected in series to each other in opposite directions, a magnetic flux detection coil has sensitivity to the change rate of the magnetic field in the Z-direction. Therefore, if a signal source is present in a close range and a noise source is present at a long distance, only a desired signal component can be taken out. For example, if irregularity is generated in the outer diameter of a substrate 5 and the relation between the areas A1, A2 of the loops is A1>A2, the relation between the inductances L1, L2 of the loops 1, 2 comes to L1>L2. In this case, a pad 3 is irradiated with light R1 through an optical fiber 8 to lower the permeability of the pad 3 so as to obtain L1=L2. By this method, a noise current is reduced and magnetic flux can be measured at a good S/N ratio.