| 摘要 |
PURPOSE:To detect the position of a tone arm, by measuring eddy current which changes by the relative position between a high frequency coil and a sensor plate made of a good conductor such as aluminum, etc. CONSTITUTION:When a sensor plate 3a is put close to a coil 2a, a space 7 is reduced. Then an eddy current is produced in the plate 3a by a high frequency current flowing to the coil 2a, and a magnetic flux which is contrary to that produced from the coil 2a is produced. That is, the high frequency voltage is produced across a resistor 4 by the high frequency current flowing to a coil 2 and the resistor 4. This high frequency voltage changes by the relative shift between a sensor plate 3 and the coil 2, and therefore the DC voltage delivered from a rectifying circuit 5 is always set at a certain level corresponding to the change of the relative position between the plate 3 and the coil 2 if the high frequency voltage is rectified through the circuit 5. This DC voltage is compared with the reference voltage through a voltage comparator 6. As a result, the position is detected for the sensor plate 3. |
