food & drink processing 31
difference between a health profit and a catastrophic
loss.
This all sounds very useful, and actually measuring
torque can be very simple. Not so long ago torque
sensors required a fairly complicated and fragile array of
slip rings connected to the rotating drive shaft of the
machine under test.
But now TorqSense provides a digital, non-contact
means for taking the readings. In use, a couple of ‘pads’
are fixed to the shaft of the sensor and a digital
TorqSense electronics module unit mounted close by.
The TorqSense then starts monitoring torque, and
feeding it as a data signal to the SCADA control system.
Principles
The ‘pads’ contain in fact tiny piezoelectric acousic wave
combs. The spacing of these combs are designed to
open or close under the torque being applied to the
drive shaft. The greater the applied torque, the more
the distortion.
The digital TorqSense unit then emits a low powered
Fig. 2. TorqSense trasnsducers can be used to monitor the flow character-
radio frequency signal towards the combs, which are
istics of foods as diverse as curry, chocolate and pasta sauce.
reflected back to the TorqSense unit. The reflected
signal returns as a changed frequency, the change being locations.
propotional to the distortion of the combs, and thus to The cyclic nature typical in many pumps’ operation
the applied torque on the drive shaft. tends to induce torsional oscillations in the drive shaft,
The phyical phenominum which deforms the combs which can have a significant adverse effect on
is called surface acoustic wave (SAW), a property first performance if unchecked.
noted in 1885 by gentleman-scientist Lord John William CAP has recently built a new test station based on
Strutt Rayleigh. He postulated many possible uses for Sensor Technology’s TorqSense sensors, and it is proving
SAWs, but was unable to realise any practical use for his it's worth time and time again. Advantages of SAW
theories. techniques include a broader signal bandwidth than
It was not until the 1920s that SAWs were shown to be other analogue based technologies and elimination of
generated by the moving edges of earthquakes and electronic interference.
avalanches, the recording of which using low frequency As CAP found, it often also proves far lower cost,
vibration monitors formed the basis of modern simpler to use, is more reliable and has a wider
seismology and volcanology. operating than contact alternatives.
By mid 20th century scientists were creating SAWs
devices in laboratories and developing new ideas for
Currying flavour
their use. As the century closed Sensor Technology Ltd Real time process control for food manufacture involves
were using the phenomenon to develop a new method characterising the flow and mixability of highly non-
of digital torque measurement and monitoring, the Newtonian fluids. TorqSense transducers monitoring the
non-contact nature of which promised to be very constantly changing flow characteristics of materials as
attractive to working engineers. diverse as tomato ketchup, chocolate, pasta sauce and
chicken tikka massala as they are mixed.
Applications
Many manufactured foods are presented in a sauce
Charles Austen Pumps (CAP) has recently upgraded its or as what physicists could describe as a neo-liquid and
test facilities with Surface Acoustic Wave (SAW) can be produced in a process-type environment. But to
TorqSense equipment from Sensor Technology. date real time control has been virtually impossible due
Charles Austen Pumps manufactures pumps to the non-uniform nature of the food, which may
individually designed to meet specific customer contain particulates, fibres, vegetables, meat, nuts,
requirements that cannot be satisfied by off-the-shelf raisins, biscuits etc.
units. To achieve real time control the TorqSense has to be
Much of its work comes down to optimising drive able to detect the changes with sufficient sensitivity, yet
dynamics to produce the desired characteristics, be it a be robust enough for general industrial abuse. Of course
smooth flow in a critical medical situation, ultra low it must not compromise hygiene standards and regimes
noise for pumps in home and office installations, or the either.
guaranteed extra long life of pump in inaccessible TorqSense has been found to meet all these
☞
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