| 摘要 |
PURPOSE: To establish an absolute relationship between a pointer position and a control system without requiring any external sensor by shifting the pointer with respect to a stopper thereby detecting the locked movement of the pointer. CONSTITUTION: The maximum amplitude of the output voltage from a coil 5 is determined at two sequential positions of a rotor 28 under control of a logic circuit 12 and the absolute value of the difference is normally constant. When a pointer abuts against a stopper, the rotor 2 can not turn any more and since equal maximum values are obtained at two following parts, a value 0 appears on the output side of a subtractor 18. In this regard, a fixed value generator 21 sets a specific threshold value and when it is exceeded, a comparator 20 delivers a control signal for notifying the arrival of the pointer at the stopper to the circuit 12. Consequently, a signal generator 9 is interrupted and the rotary load on the rotor 2 is stopped, thus avoiding mechanical overload on a three-phase AC motor 1. |
