Sensor technology proves key to plant teaching 30 April 2010

The electrical machines laboratory at Dublin Institute of Technology (DIT) is a better teaching resource since TorqSense non-contact torque sensors, from Sensor Technology, were fitted to five machine sets.

The new sensors replace a system of machine monitoring that had proved inaccurate.

To provide maximum flexibility, the demonstration equipment is modular, so that experiments with both ac and dc machines can be carried out on the same test bed.

Whatever the configuration, however, the experiments require monitoring and collection of a number of key operating parameters, including torque, speed and power.

"We had tried many methods for measuring these parameters, but had found it impossible to get results we could rely on, particularly in the case of the torque and power measurements," explains Terence Kelly, technical officer at Dublin Institute of Technology.

"Then we heard about Sensor Technology's products, and after we'd visited the company and seen the sensors in action, we knew that they we'd found the solution."

The sensors that attracted his attention depend on surface acoustic wave (SAW) transducers, which comprise two thin metal electrodes in the form of interlocking fingers on a piezoelectric substrate. 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 is that if the substrate is deformed, the resonant frequency changes. When the transducer is attached to a motor drive shaft, that frequency change relates to the torque applied to the shaft – meaning that the transducer becomes a frequency-dependent strain gauge.

Since the transducers operate at radio frequencies, it is easy to couple signals to them wirelessly. Hence, they can be used on rotating shafts, and provide data continuously, without the need for brushes and slip rings.

"The biggest benefit is that they use a wireless connection between the transducer itself and the sensor electronics," comments Kelly. "This solves all of the major problems at a stroke. But they also excel in terms of the amount of information they collect, and because they deliver measurements of all key parameters in real time."

Brian Tinham

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