Eddy-Current Brake Dynamometer Hysteresis in Engineering Technology Education Test Beds: A Torque-Reference Calibration Linking Magnetic Saturation to Load-Setting Repeatability Bounds

Eddy-current brake dynamometers are widely used in engineering technology education as load-setting test beds, yet their torque output exhibits hysteresis that is rarely quantified against a traceable reference. The framework treats the brake as a saturable magnetic circuit and derives a closed-form expression for the hysteresis loop width as a function of excitation current, disc permeability and air-gap reluctance. A calibration protocol is specified in which a reference torque arm and a strain-gauge load cell establish the ascending and descending torque-current branches, from which a repeatability bound is computed at the 95% coverage level. The analysis is methodological and does not report empirical measurements; instead, it formalises the conditions under which hysteresis becomes the dominant contributor to load-setting uncertainty and derives the excitation range over which the bound remains within a stated tolerance. The principal contribution is a design-stage procedure that allows educators and technicians to predict whether a given eddy-current dynamometer can meet a specified repeatability target before a laboratory exercise is commissioned. The framework is intended to support the accreditation of test beds used in mechanical and electrical engineering technology curricula.