实际的装载量靠近极限值的同时，又不断与四个极限值相比较。起重机控制电容可以作为开关。
The actual load is compared to four limit values, and by achieving the limit value, the relay of the crane controller could be switch.
本实用新型只需扳动一个开关，起重机吊臂的 伸缩动作可自动连续完成。
The device can realize the automatic and continuous telescopic motion of the suspension arm of the crane only by flipping one switch.
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