Torque measurement alternatives for rotating shafts

To determine the torque and power output and efficiency of engines, generators, electric motors and gearboxes and the stresses in drive shafts and other machine components, designers often have a need to measure the torque in a rotating shaft.

This is generally accomplished by using strain gauges attached to the rotating shafts or torque transducers which have strain gauges attached to specially machined strain sensing elements.

To provide the power and capture the signals from the strain sensing elements, traditionally slip rings were used. These had the disadvantage of being noisy and of limited life so alternative methods of power transmission and signal capture were developed. Initially, rotating transformers were used for both power transmission and signal capture. Such transformers could only be used on torque transducers and were not suitable for mounting on to shafts.

Very recently, a different method of power transmission and data capture has been developed by including strain gauge signal processing and the RF transmission of data on the rotating shaft with a stationary aerial mounted near the shaft for power transmission and data capture. This new data acquisition system is totally digital giving improved accuracy and gives you much more flexibility in the mounting of the aerial which can be inside a gearbox or up to 700mm from a vehicle’s drive axel. This new telemetry system is equally applicable to torque transducers and to strain gauges mounted on a shaft.

With a precision torque transducer, it is possible to achieve better than 0.1% accuracy however when gauges are mounted on a shaft the accuracy is generally <1% as the strain levels are less and extraneous forces may be present.

Torque transducers are used when:

  • precision is required

Rotary telemetry systems are used when:

  • strain gauged shafts are used
  • when it is not possible to cut the shaft and install a transducer because of space constraints or costs
  • or, when the strength, mass or stiffness of the shaft is compromised by the addition of the transducer

Hylec has had experience in offering torque measurement solutions, including precision Himmelstein rotating torque transducers and Caemax digital rotary telemetry systems, for over 30 years. To enquire, simply visit