Rugged torque transducer selected for aerospace dynamometer

Automated Technologies is a design and engineering company that develops novel automated systems, innovative products, prototyping programmes and equipment for solving process engineering problems. Over its many years' experience developing new technologies for demanding clients in all major sectors of industry, it has come to rely on UK manufacturers, as Chief Engineer Chris Baxter explains: "Building bespoke machinery and developing prototypes, as we do, is a very collaborative process. Quite often we need considerable support from our suppliers as we work through a knotty problem or two; sometimes this means an intense hour-long engineer-to-engineer phone call, or a visit to their premises. It is hardly surprising that this is easier with local companies. Of course, it is also nice to think that we are doing our bit to support the nation's engineering base."

With its history of innovation, Automated Technologies was a natural choice to design and build the new dynamometer. With the core requirement for 3000-hour continuous testing (day and night for over four months), Baxter knew that the rig would have to be very robust and that simplicity would improve the overall reliability.

The basic design features a motor that drives the test piece against a load in a closed-loop control system; the TorqSense transducer provides feedback by monitoring performance in terms of torque and speed. Variations in the performance over time indicate the level of wear the component is experiencing and, from this, safe working lifetime profiles can be developed. The data is logged to a database to allow trending to be mapped. Also a web-based real-time display enables parameters to be viewed remotely.

Rugged, non-contact torque measurement

TorqSense sensors, which are covered by patents, depend for their operation on surface acoustic wave (SAW) transducers. Follow this link to read about how surface acoustic wave (SAW) transducers work.

Since the TorqSense SAW transducers operate at radio frequencies, it is easy to couple signals to them wirelessly. TorqSense sensors can therefore be used on rotating shafts and can provide data continuously without the need for the inherently unreliable brushes and slip rings that are often found in traditional torque measurement systems.

This simple wireless operation was very attractive to Baxter. It means that test runs can be set up quickly and easily and, in long-term tests, a radio-frequency link is likely to prove more reliable than a slip ring.

Given the long duration of the tests, Baxter was concerned that the dynamometer would consume a large amount of electricity and be costly to run. However, he was able to mitigate this to a large degree by using a generator as the driven load. The power created could therefore be fed back to the motor in a closed-loop configuration, reducing the motor's power draw from the mains.

An Invertek variable-speed drive (VSD) is used to alter the speed of the motor and the operating conditions of the component. Speed profiles can be used to emulate the cyclic nature of use experienced during multiple flights, or to subject the components to extreme testing to determine their failure mode characteristics.

Significantly, the generator was required to be of brushless design and hence had to produce a three-phase output, and the motor is also a three-phase unit as these are better balanced to reduce susceptibility to harmonics in the drive-train as the machine speed is varied.

Follow the link to learn more about the TorqSense transducers from Sensor Technology.