Phase Shift Principle
This simple form of phase shift torquemeter is well known. As torque is applied to the rotating shaft, a change of phase is produced between the signals of two pickups. However, large inaccuracies are introduced by any relative radial and axial movements between the shaft and the pickups.

Torquetronic system
The 'Torquetronic system's key feature is the use of a pair of multipole pickups in the form of internally toothed rings, which provide compensation for any relative movement between shaft and stator.

The circumferential pickup/field coils provide a torroidal flux path so that as the shaft rotates, the teeth generate sinusoidal signals in stationary coils. Phase displacement is directionally proportional to shaft twist and hence torque.

As the amount of twist generated by the torque applied is proportional to the Young's Modulus of the material of the shaft, an extremely stable, reliable and repeatable measurement is obtained.

Rotastat feature
'Torquetronic' test stand models feature a built in Rotastat system in which the pickup teeth can be rotated to generate signals with the shaft stationary. This allows static calibration with lever arms and weights and zero speed torque measurement.

The calibration constant of the system is simply the torque to twist the shaft through one tooth pitch which must clearly correspond to exactly 100% phase displacement. The stiffness of the high tensile stress shaft is as stable as Youngs modulus and exceptionally linear.