Sensor Technology torque sensor used in mini mixer

The Sensor Technology TorqSense torque sensor is being used in developing a mini mixer to help analyse mixing properties at the University of Bradford.

The miniature mixer (5-25g batch) incorporates a set of integral instruments to monitor the properties of materials as they are being mixed.

One of the key parameters to be measured is the torque of the mixing element, as this will become constant once mixing is complete.

This is measured by a TorqSense non-contact sensor that offers the development team the great advantage of not requiring complex and delicate slip rings, making the mixer easier to build (and rebuild between trials) and far more robust in operation.

TorqSense sensors use two tiny ceramic piezo-electric frequency resonating combs, otherwise called Surface Acoustic Wave (SAW) devices that are fixed onto the shaft of the torque sensor to measure applied torque.

As the torque changes the combs vary their spacing and the resonant frequency of the SAWs changes proportionally to the torque applied in the rotating shaft.

In effect the combs are frequency-dependent strain gauges that measure changes in resonant frequency of the shaft.

A wireless radio-frequency (RF) coupling is used to interrogate the SAWs and transfer the data signal to a pickup head.

The same RF coupling is used to supply power to the SAW devices, and because the gauges are based on piezo technology they need less than one milliwatt of power.

This arrangement completely eliminates the difficulties of fitting slip rings and maintains the measurement quality throughout an extended test run.

TorqSense embraces all the advantages of SAW technology, including no load imparted or extra drag to the drive mechanism under investigation.

As it is fundamentally a digital system it has a broader signal bandwidth than analogue-based technologies, and electromagnetic interference is eliminated.

The instruments work in real time during the mixing process and their output is captured to a PC for subsequent analysis.

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