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Ocean Flow Energy has used a surface acoustic wave (SAW)-based Torqsense transducer under the sea as part of extensive trials of its Evopod green-energy turbine.

In a Torqsense transducer, surface waves are produced by passing an alternating voltage across the terminals of two interleaved comb-shaped arrays, laid onto one end of a piezoelectric substrate.

A receiving array at the other end of the transducer converts the wave into an electric signal while tension in the transducer reduces the operating frequency and compression increases it.

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 that is transmitted to a stationary pick-up via a capacitive couple comprising two discs — one of which rotates with the shaft, the other being static.

Key benefits of product application

  • Measures the torque and rotational speed of the turbine
  • Indicates the power that can be derived from the system, as well as giving an indication of the stresses on the turbine
  • Reliable in challenging applications

Sensor Technology

Sensor Technology are manufacturers of TORQSENSE Transducers, the world’s first low cost non-contact rotary torque transducers designed for OEM applications. Rotary torque measurement has always been difficult and expensive.

The patented method uses a surface acoustic wave device as a frequency dependent strain gauge and measures the change in resonant frequency caused by the applied strain in the shaft.

The signal is transmitted via an RF couple from the rotating shaft to a fixed pick-up.

By using a frequency-based device, the signal bandwidth is increased, and the problem of electronic interference common with analogue signals is eliminated. The torque sensors are designed to operate direct from a PLC or a PC.

They require minimum length of shaft, have low inertia, no physical contact between shaft and housing, wide bandwidth, high resolution and accuracy resolution to better than one part in a million, and excellent noise immunity.

The technology lends itself to design of OEM transducers for specific customer applications. Applications include automotive, manufacturing machines, condition monitoring where knowledge of torque is critical, torque control of tightening procedures, and monitoring of viscosity during mixing where consistency is required. The technology replaces existing types of rotary torque sensors by providing better performance at a lower price.

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