Sensors & transducers

Wireless torque measurement at the heart of distribution netWork controller test rig


quar tz. When an RF signal of the correct frequency is applied to the transducer, surface acoustic waves are set up, and the transducer behaves as a resonant circuit. The key feature, however, is that if the

substrate is deformed, the resonant frequency changes. When the transducer is attached to a drive shaft, the deformation of the substrate and hence the change in resonant frequency will be related to the torque applied to the shaft. In other words, the transducer, in effect, becomes a frequency-dependent strain gauge. Since the transducers operate at radio

frequencies, it is easy to couple signals to them wirelessly. Hence, the TorqSense sensors incorporating the SAW transducer technology can 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. In the Hy-Pro application, a TorqSense

sensor is used to measure the torque applied to the pump over the critical speed range of 500 to 4,000 rpm. The results are displayed in real time, so that the progress of tests can be readily monitored, and are also captured and stored for more detailed analysis later with Labview software. “The TorqSense sensor has proved to be

completely dependable and very accurate,” says Wynn. “The data it has provided us with has played an impor tant role in helping us to refine our systems by ensuring an optimum match between the characteristics of the pump and motor over the full operating range.” “In fact, the insights we’ve gained during

our tests have enabled us to fur ther enhance the performance and reliability of our steering and autopilot systems, which, of course, means big benefits for our customers and a very useful boost to our own competitive position.”

Sensor Technology 58

ver the last 10 years, the UK’s electricity generation mix has changed substantially. Where coal

fired power stations made up some 37 per cent in 2008, that has fallen to less than eight per cent today. Our reliance on gas continues to be a concern: it made up around 40 per cent of the fuel mix ten years ago, but still represents around 35 per cent of our fuel mix today, with the government worried not only about longevity of supply, but also stability. Nuclear power today represents around 15

per cent of the UK’s energy mix, and while there is a commitment to building new plants, there have also been slips in the construction timetable and escalating budgets. Meanwhile, at the same time, the numbers of options for renewables have been increasing and the costs have been falling. There is an attraction in moving away

from the centralised power plant model for energy generation to one where smaller, renewable energy plants are constructed, using distribution networks either to connect to the transmission network or to supply local energy requirements directly. The range of these alternative power plants being constructed include wind farms, hydro-electric stations, solar farms, CHP and biomass combustion plants, as well as a host of other smaller generation technologies. However, the surge in the number of

distributed generation plants and the resulting increase in the numbers of connections to distribution networks does not come without problems, par ticularly when the variability of supply from the likes of wind and solar farms is considered. Unlike conventional centralised power stations, these renewables produce less stable supplies, of variable quality, so are difficult to connect to the grid. The development of new controls that

will enable renewable distributed generators to supply either local requirements or to be connected to the transmission line grid is the subject of a PhD project at the University of Warwick. Researcher Ruizhu Wu is studying the use of power electronic devices to increase the penetration level of distributed generation in distribution networks. Power electronic controllers are seen as one of the primary options to control the power flows and voltages that will enable new loads to be integrated into the distribution network, and so increase the density of distributed generation. But there are still challenges to the

The rig is built around two induction machines which mimic the generator and load. The TorqSense transducer between the two is used to map the performance of the machines, enabling voltage and current to be linked with torque and so provide an accurate picture of the requirements of a controller. The wireless TorqSense transducers

operate using surface acoustic wave (SAW) principles, and offer significant advantages compared with strain gauges, magnetic torque sensors and optical devices that might be fitted conventionally. Each TorqSense sensor uses two tiny SAW devices made of ceramic piezoelectric material containing frequency resonating combs. These are glued onto the drive shaft at 90 degrees to one another. As the torque increases the combs expand or contract proportionally to the torque being applied. In effect the combs act similarly to strain gauges but measure changes in resonant frequency. The adjacent RF pickup emits radio waves

towards the SAWs, which are then reflected back. The change in frequency of the reflected waves identifies the current torque. This arrangement means there is no need to supply power to the SAWs, so the sensor is non-contact and wireless. The research is at a very early stage, with data only now beginning to be assessed. But power electronics is regarded as providing a real turning point evolution of distribution networks to enable the integration of a greater number and a wider range of distributed power sources. April 2019 Instrumentation Monthly

widespread deployment of power electronic controllers in distribution networks. Ruizhu Wu’s work is focused on identifying the requirements of the necessary power electronic controller, and to do this he has built a test rig to simulate variable loads. Key to the research is a TorqSense wireless torque measurement transducer from Sensor Technology.

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