Contactless Torque Monitoring

Continuous Monitoring for Torsional Vibrations

In the last years we have developed the software tools TorStor, TorFat, TorGrid and TorAn, which together with the contactless torque sensor exclusively distributed by us each form a torsion detection and analysis system of varying complexity. 

Depending on the application, we record relevant torsional oscillations with the respective system and evaluate, visualize and analyze them in the time and frequency domain with the integrated visualization tool TorVis. In addition to long-term monitoring, they are also successfully used to determine torsional natural frequencies and mechanical damping constants of drive trains.

Our systems are installed in power plants worldwide on behalf of companies. Beyond the power plant sector, our systems are suitable – in principle – for torque monitoring and analysis on shaft line with ferromagnetic surfaces. In particular, our systems represent an ideal extension of condition monitoring systems for many applications. We would be pleased to integrate them into your product.

Condition Monitoring Systems at Fraunhofer ITWM

The tasks involved in the torsion monitoring of drive trains are manifold. In the following, we present the developed methods and software tools for the different problems. Our systems are supplied with an inductive sensor for contactless torque measurement. Here we present our developed methods and software tools:

Screenshot TorVis – TorGrid
© Fraunhofer ITWM
Screenshot TorVis – TorGrid

TorGrid – Monitoring of Grid Repercussions on Conventional Energy Producers

Due to the significant increase in the feed-in of renewable energies and the coupling of high-voltage direct current transmission via inverters, new types of dynamic effects are occurring in the electrical grid. In particular, the treatment of previously unknown grid repercussions on conventional power generation units plays a role here.

We have developed the online monitoring system TorGrid to monitor grid feedback on power plant drive lines. This tool synchronously records the torsional oscillations of the shaft train and the three-phase currents and voltages at the generator and at the transformer on the grid side. Based on intelligent trigger criteria, TorGrid monitors the measurement signals and thus detects the events that the user considers critical. In addition to the measured values from up to three non-contact torque sensors and the three instantaneous currents and voltages, TorGrid also stores the power of the generator and the transformer on the grid side, determined from these measured values.

With TorGrid, our customers in the conventional power plant sector can plan their inspection and service activities even better. The long-term goal is to use the signals recorded with TorGrid to compensate for grid feedback.

Analysis of the Interaction Between Grid and Turboset

The integrated TorVis visualization software for TorGrid allows subsequent analysis of the stored torque, power, current and voltage curves in the time and frequency domain. The software thus offers the user the possibility of analyzing the cause of the torsional load on the shaft train at the time of the detected event: external feedback from the electrical grid, oscillations triggered by internal mechanisms at the generator itself or interactions between the turbine set and the electrical grid - these include, for example, subsynchronous resonances.

TorAn – Online-Monitoring of Endangered Areas of a Drive Train

TorAn is a tool for online monitoring of torsional vibrations and for fatigue analysis of rotating machines. Based on a robust observer, TorAn estimates online the torsional oscillations at the user desired points at the shaft line based on the excitation torque as well as a torsion measurement of the contactless sensor. Thereby the number of required sensors is reduced to a minimum.

TorAn detects relevant torsional events and calculates the fatigue of the desired system components after each such an event. The fatigue, the maximum torque moments and stresses that occurred and the ratio between maximum and permitted torque moments are provided in tabular form after their calculation. The visualization of the stored events time series is also possible with TorAn.

TorStor – Recording of Relevant Torsional Oscillations

TorStor is used when it is necessary to determine characteristic data of the drive train experimentally or from long-term measurements. For this purpose, TorStor has various criteria for storing the measurement data as well as an oscilloscope with which the torsional vibration behavior can be observed during the measurements.

The signals acquired with the non-contact torque sensor are transferred to a PC via a data acquisition board. TorStor is first used to configure the data acquisition board for torque measurement. In addition, the voltages applied to the data acquisition board are converted into electrical torques and stored in files with a length of 20,000 data points each.

The stored torque curves are displayed in the time and frequency domain by the integrated TorVis visualization tool.

TorFat – Measurement Data Based Detection and Evaluation of Critical Torsional Oscillations

TorFat is a tool for online monitoring of torsional vibrations and fatigue analysis of rotating machines at the measuring trace. For this purpose, TorFat requires information about the geometry and material data at the measuring trace.

TorFat analyzes the measured torsional oscillations and checks if a relevant failure is present. If this is the case, a fatigue analysis is performed for the monitored component and added to the damage already calculated.

The main results of the damage analysis are provided in tabular form. The failure can be displayed in the time and frequency domain with the integrated visualization tool.

Contectless Torque Acquisition
© Fraunhofer ITWM
Our systems are supplied with an inductive sensor for contactless torque measurement.

Contactless Torque Monitoring

We supply our systems with an inductive sensor for contactless torque measurement. The measuring principle of the sensor is based on the Villary effect in ferromagnetic materials. Here we take advantage of the fact that the permeability in tensile and compressive direction is different in these materials, e.g. in case of torsional stress. Without torques, the permeability of the shaft is theoretically identical in both tension and compression directions. Therefore, the magnetic field in these directions is also the same. If torques are present, the permeability of the shaft material is different in the tension and compression directions. The sensor measures this difference inductively, which is proportional to the surface stresses or torque over a wide measuring range.

Technical and Geometrical Data




Input voltage DC

12 V

5 Percent

Power consumption

40 mA

5 Percent

Output signal

0-4V or 4-12mA with converter box (see below)


Resolution output signal

12 bit





Temperature range



Temperature compensation



Zero point adjustment

Yes, with included Software





Housing material



Cover material (Connector side)



Material coil side








1 Percent

Height without plug


2 Percent

Height with plug


2 Percent

Measuring head diameter


1 Percent




Converter Box



Hardware revision



Housing material

ABS plasitc


Input voltage



Power consumption




4-20 mA differential with ground wire