The outputs of turboshaft engines commonly include a "torquemeter" that measures the speed and torque transmitted through the output shaft. The torquemeter often consists of a pair of angular position sensors (such as Hall effect devices) and trigger wheels at opposite ends of the output shaft, which measure the torsional deflection of the output shaft under load. The engine HUMS records the accumulated shaft rotations and torque moment applied during each such event
Not sure if the EC225 uses the same system, but that exactly how the AS332 works - phonic wheels and hall effect.