| 摘要 |
PURPOSE:To detect disconnection without any detection error, and to display it, by displaying the detection of disconnection in accordance with continuation of a prescribed time, of the variation of circuit impedance due to disconnection. CONSTITUTION:When a variable motor 1 is in operation, if disconnection is generated between an AC speed generator 2 for detecting the speed of this motor, and a speed controlling circuit, the potential of a contact A rises to positive voltage decided by input impedance of a full-wave rectifying circuit 5, resistances 3, 4 and 6, etc., by the variation of the impedance due to said disconnection. As a result, an output of an operational amplifier 10 is inverted to negative potential, an output of an integration circuit by an operational amplifier 17, a feedback capacitor 20, etc. rises in the positive direction by a prescribed time constant, and when the negative potential state of the output of the amplifier 10 continues longer than the time based on the output period of the generator 2, disconnection is detected by an integration output of a prescribed value or more, and is displayed through a diode 23. Disconnection in case when the motor 1 has stopped is also directed in the same way, and it is possible to detect disconnection without causing a detection error, in case when generated voltage of an AC speed generator has become high due to increase of a speed, or due to overshoot, etc. |
