Calculating torsional natural frequencies is a common component of machine design and many specifications require a specific separation margin between calculated torsional natural frequencies and known exciting frequencies. However, a machine's actual torsional natural frequencies may not agree with what is predicted due to differences between what is modeled and what exists in the field. When the actual torsional natural frequencies coincide with a driving dynamic torque, resonance occurs and large torsional vibrations will be present. Torsional vibration can damage shafting and drive components by producing high dynamic stresses in shafting, gears, couplings, and more. When torsional failures occur, there is generally little indication prior to failure since the dynamic motion is rotational rather than translational and cannot be measured or perceived without the correct equipment.


Applicable Equipment for Torsional Vibration Measurement

Types of machinery that are commonly tested for torsional vibration include:

  • Reciprocating compressors and pumps
  • Transmission shafting with universal joint type couplings
  • Turbomachinery shafting with gearboxes
  • Variable frequency drive motors


Torsional Natural Frequency Measurement

The torsional natural frequencies can be determined by measuring either the torque or the twist of a shaft. We commonly measure the torque using strain gages and wireless telemetry. This type of torque measurement provides the static and dynamic torque in the shaft. Alternatively, the shaft twist can be measured using encoders. The dynamic torque and the twist give an indication of the torsional response of a system and with a proper test and analysis the torsional natural frequency can be determined. Below is a comparison of the dynamic torque measured during two motor starts. For this project, a torsional analysis was conducted and recommended making a change to the system to reduce the torsional natural frequency.


Kelm Engineering for Torsional Vibration Measurement

If your company or corporation is in need of torsional vibration measurements, then contact Kelm Engineering. Our trained and experienced engineers have the equipment necessary to provide your business with accurate readings in an efficient and timely manner.