Coupling system with overload protection for lifting device

摘要

The coupler uses a set of electrical contacts and a timer stage monitoring cable tension and providing delays in response to measured overloads to reduce sensitivity to dynamic loading transients. A partial loading detector operates a part-load relay (d1) while a maximum loading detector operates a maximum loading relay. A timer stage comprising a timer relay activated from the part load and full load relays gives a full time delay except when the part-load relay is inactive and the maximum load relay is active, in which case the lift power supply is immediately cut off. The timer relay is driven by a circuit comprising a resistor-capacitor network coupled into the gate of a thyristor. The coupling system detects overload on the cable without responding to transient dynamic forces.