Cable Reel Beam Limit Switch

Core working principle:
     Position monitoring: Install limit switches at the travel limit position of the crane's large, small, or lifting mechanism, and install collision gauges (trigger blocks) on the corresponding moving parts.
     When the signal triggers the moving parts to reach the preset limit position, the collision ruler contacts the operating head of the limit switch (such as the roller, lever), forcing the internal micro switch contact to change the on/off state (usually from normally closed to open).
     Power cut-off: The limit switch is connected in series in the control circuit. After the contact is disconnected, it directly cuts off the power supply of the contactor coil of the corresponding motor or sends a signal to the PLC, causing the motor to stop and brake, achieving hard limit protection. ‌‌
Key safety requirements:
     Dual limit configuration: The lifting mechanism of newly manufactured bridge cranes usually requires the installation of two different forms of limit devices (such as heavy hammer type+fire cut-off type), which are backup to each other.
     Graded protection: The operating mechanism is equipped with a permanent two-level limit, with the first level being deceleration limit (early deceleration) and the second level being terminal limit (complete power-off), to avoid inertial collision.
     Cannot rely on limit parking: The limit switch is a safety protection device and not a normal operation switch. It is strictly prohibited to rely on the limit switch for routine parking during daily operations.