| 摘要 |
PURPOSE:To eliminate the influence of temperature fluctuations, a secular change, etc., by controlling automatic balancing by using a variable impedance element for one side of a bridge circuit which detects the moving speed of a condenser. CONSTITUTION:A moving-speed detection voltage V obtained by finding a difference in voltage between the points B and C of a bridge circuit 21 by a subtracter 27 is accumulated in the hold capacitor 45 of a sample holding circuit 39 through a low-pass filter 44. The output of the sample holding circuit 39 is sent to a variable impedance element 38, and consequently a variable impedance element 38 is so controlled that the sample holding circuit 39 is balanced. If the output of a control oscillator 40 goes up to a high level in a bridge-balanced state, a changeover switch 41 is changed over to a contact 41b, and the switch 43 of the sample holding circuit 39 turns off, so that a condenser 10 fitted to a coil 20 approaches a disk at a constant speed. |
