Wireless torque sensor cuts out slip rings

At the Sensors & Instrumentation Exhibition 2013, Sensor Technology will show a new, wireless technology for measuring power in drive shafts and other rotating machine elements.

TorqSense Rotary Torque Sensors are unlike traditional slip ring transducers, using a simple non-contact radio link for collecting real-time torque signals. This means that machine builders and control engineers can do away with expensive and temperamental slip rings – instead, simply mounting the sensors and checking the radio connection.

Electronics convert the data stream directly into engineering outputs, such as torque, speed, power and angle. Serial and USB interfaces make TorqSense directly compatible with PCs and other user-friendly features include built-in peak torque sampling, storage and torque averaging, and a self-diagnostics test package.

To achieve the non-contact operation that makes the TorqSense transducer range unique, SAW (surface acoustic waves) devices are used as frequency-dependent strain gauges to measure the change in resonant frequency, caused by strain experienced in the driveshaft. This measurement is directly related to the torque experienced in the rotating machine element.

To measure the torque in a rotating shaft, two SAW sensors are bonded to a shaft at 45° to the axis of rotation. When the shaft is subjected to torque, a signal is produced, which is transmitted to the adjacent stationary pick-up via the capacitive RF couple comprising two discs, one of which rotates with the shaft, the other being static.

The frequency of the oscillation used is typically 200MHz. The frequency-basis of the TorqSense concept gives a wide bandwidth and the susceptibility to electronic interference, common with other analogue-based techniques such as inductive devices, is eliminated.

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