| 摘要 |
PURPOSE:To eliminate the disturbance due to an induced magnetic field through offset compensation by detecting a magnetic field induced by an auxiliary magnetic pole or a main magnetic pole and driving a compensating coil with use of a detection signal to produce a magnetic field having the polarity opposite to said induced magnetic field. CONSTITUTION:A main magnetic pole 2 and an auxiliary magnetic pole 3 are provided, and a magnetic field detecting element 7 is attached to the lower end of the pole 3. The element 7 detects the upper and lower magnetic fields induced from outside to the pole 3. A compensating coil 8 is wound at a position peripheral to the pole 3. The polarity of the magnetic field generated by the coil 8 is set opposite to that of the induced field detected by the element 7. Thus the induced magnetic field is offset and has no disturbance. Generally the frequency of an external magnetic field is lower than the signal frequency of a record/reproduction mode. Thus an external induced magnetic field can be assuredly checked by means of an LPF10. This LPF is effective to the magnetic fields of low frequencies which occupy the greater part of induced magnetic fields. |
