| 摘要 |
It is possible to monitor the state of each on/off mechanical contact or on/off semiconductor device of a motor contactor and brake contactor of a driving circuit supplying driving electric power to a three-phase alternating-current electric motor and a brake of an electric lifting-lowering device through the motor contactor and the brake contactor, respectively, and to detect a reverse phase of three-phase alternating current before the contactor is turned on. Detecting circuits 6a to 6e are connected in parallel to respective on/off mechanical contacts or on/off semiconductor devices of a motor contactor 2 and/or a brake contactor 4 of a driving circuit supplying driving electric power from a three-phase alternating-current power supply circuit 1 to a three-phase alternating-current electric motor 3 and a brake 5 through the motor contactor 2 and the brake contactor 4, respectively. The detecting circuits output pulse signals synchronized with the alternating current from the alternating-current power supply circuit. A signal processing circuit 7 processes the pulse signals from the detecting circuits and detects a normal or abnormal condition of each on/off mechanical contact or on/off semiconductor device of the motor contactor and/or the brake contactor. |
