Abstract: A device for the calibration of the safe load indicating apparatus on cranes and derricks that have a pivoted, extensible boom luffed by a hydraulic ram. The device operates by combining electrical signals corresponding to the actual turning moment of the unloaded boom at given boom positions with generated calibration signals corresponding to the turning moment for the theoretical maximum load at the boom positions, by comparing these combined signals to the safe load signals from the crane's law generator unit and by adjusting the law generator unit accordingly.This invention relates to a method and apparatus for the calibration of safe load indicating apparatus for use with cranes, derricks and other lifting apparatus of the type having a pivoted, extensible boom which can be luffed by an hydraulic ram or other boom supporting means.

Abstract: A crane load indicator in which actual loading is determined by a strain transducer as a function of shear stress on a crane boom. A resultant actual loading signal is compared with a computed signal representative of the maximum crane loading for the prevailing conditions and the two signals are compared to provide an indication of available lifting capacity.