The electrical machines laboratory at the Dublin Institute of Technology (DIT) has greatly increased in its effectiveness as a teaching resource since TorqSense non-contact torque sensors from Sensor Technology have been fitted to five machine sets. The new sensors replace an existing system of machine monitoring that had proved inaccurate.

To provide maximum flexibility, the demonstration equipment in the DIT machines laboratory employs modular construction. This means, for example, that experiments with both AC and DC machines can be carried out on the same test bed, as whichever machine is needed is simply clamped into place.

Whatever the configuration of the equipment, however, the experiments and demonstrations performed in the laboratory require the 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,” said Terence Kelly, Technical Officer at Dublin Institute of Technology. “Then we heard about the Sensor Technology’s innovative products, and after we’d visited the company and seen the sensors in action, we knew that they we’d found the solution we were looking for.”

The sensors that attracted the attention of DIT depend for their operation on surface acoustic wave (SAW) transducers. These transducers comprise two thin metal electrodes, in the form of interlocking “fingers”, on a piezoelectric substrate such as quartz. 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 motor drive shaft, the deformation of the substrate and hence the change in resonant frequency is 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, TorqSense sensors that incorporate 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.

Other features of these novel sensors include a large safe overload margin, high accuracy and resolution, ability to operate equally well clockwise and anti-clockwise, and integral temperature monitoring. Also, as well as measuring torque, the sensors also provide speed and power data.