| 摘要 |
A variable speed motor control system for controlling the vertical speed of a hoist. An electro-mechanical brake means locks the hoist load in place when the system is off or when the motor speed is set at a zero speed setting. A quick response circuit is connected into the system for a predetermined time duration after the system is switched from a zero speed to any speed setting (high or low speed), to enable the motor to quickly gain control over the load and prevent the load from slipping as the motor accelerates to the set speed after the brake is released. An initial delay timer is turned on when electrical power is first connected into the system, to prevent transfer of electrical power to the motor and to prevent release of the brake, for a predetermined period of time. A hoist (up-down) electro-mechanical contactor connects electrical power from a source to a thyristor static switch. The system is reset to a start point and the thyristor switch is turned off, when the hoist switch is switched to an off-position but prior to the corresponding line switches breaking their connection with the thyristor switch.
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