Product Details Supplier Info More products

A Torqsense wireless torque sensor from Sensor Technology is to be used on prototypes of a hydroelectric turbine design being tested by Kingston University to illuminate the River Thames in London.

The turbine will sit on a pontoon and will provide a floating test and measurement laboratory that will be deployed in the river.

The turbine under test has been developed by Hales Marine Energy near Eastbourne and is expected to be deployable in tidal seas, as well as rivers.

The design application of this turbine is to sit on a submergible tank that will sit on the sea bed and can be floated up to the surface when required.

The design is said to be almost infinitely scalable, with the unit under test measuring 1m in diameter and producing about 1kW.

5m turbines suitable for inshore deployment would generate round 20kW, while smaller units would be ideal for river use.

‘The critical measurement is torque, as this indicates the power we can derive from the system,’ said Rod Bromfield, senior lecturer at the Faculty of Engineering at Kingston University.

‘We had to be certain that we would get continuous measurements over an extended period of time, because we need to map power production against actual river flow,’ he said.

‘Also, for this technology to succeed in the emerging green power market, it must be capable of continuous and predictable energy production,’ he added.

One of the engineering issues that the team faced was the relatively slow revolution of the turbine in this test below 50rpm.

This helped define the choice of the Torqsense, but it is also a key feature of the Hales turbine as the slow speed means less stress on moving parts and therefore less servicing.

It also minimises habitat disturbance, so that the ecological impact is low.

‘When I contacted Sensor Technology I was very concerned about vertical mounting and harsh environment performance,’ recalls Bromfield.

‘Fortunately there have been Torqsenses installed vertically, including several high up on vertical-axis wind turbines, where they have to withstand gales, hurricanes and lashing rain,’ he said.

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.

The frequency is dependent upon the spacing of the teeth in the array and, as the direction of wave propagation is at right angles to the teeth, any change in its length alters the spacing of the teeth and hence the operating frequency.

Tension in the transducer reduces the operating frequency, while compression increases it.

To measure the torque in a rotating shaft, two saw sensors are bonded to a shaft at 45deg 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 while the other is static.

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.

View full profile