By projecting a light beam of known intensity along the length of the shaft, through both discs to a photoelectric detector, the amount of twist can be measured and the torque in the shaft calculated. This was a major technological breakthrough and was a boon to
machine builders and plant operators who could now monitor and record the torque in their drive shafts in real time. This let them calculate how much power was passing through their drivelines, so that they could optimise designs and profile workloads in order to maximise overall efficiency. In fact optical torque
measurement was so successful that Sensor Technology was kept busy for the next 25 years. However, the company did not rest on its laurels: it built up a research and development team tasked with the dual goals of improving the optical technology and looking for alternatives that could be even better.
By about 1990 Sensor Technology could see that fresh innovations needed to be explored so that boundaries could continue to be pushed. With some demanding projects on the horizon in sectors like defence and aerospace, marine propulsion and medical machinery, the company was granted Link Programme funding to explore a radical new idea. Whilst conducting research on a separate project using SAW (Surface
Acoustic Wave) filters, it had become apparent that these SAW filters were sensitive to strain or torque. When torque is applied to a shaft to which SAWs are fixed, it causes a deformation of the quartz substrate of the SAW device which, in turn, causes a change in its resonant frequency. Essentially the SAWs act as ‘frequency dependent’ strain gauges. Thus Sensor Technology had devised a new method of measuring
these SAW devices as an indicator of the torque level in a turning shaft. More work was required, but by the middle of the decade they had perfected a surface acoustic wave detector that could be mounted close to a shaft and react to its torque. A new chapter in drive management was beginning. Once again, Sensor Technology’s new SAW sensors collected the
signal using a wireless RF rotating couple rather than slip rings, so they had all the ease-of-use of the previous generation sensors. Further, the same electronic processing and calibration was used to generate precise torque measurements and by this time the electronics were highly capable, sophisticated and user-friendly. SAW devices also proved to have a high immunity to magnetic
fields, allowing their use in motors and other electronically-hostile environments. They are bi-directional and provide fast mechanical and electrical responses. As the method is non-contact it has also complete freedom from brushes or complex electronics. All told, SAW-based torque monitoring advanced the state of the art
to a new level that allowed a further widening of its applicability – and another couple of decades of advancement followed.
By around 2015 the boffins were again worrying about technical limits to their technology and began looking for the next innovation. Their finding was perhaps a bit surprising: they went forward to the past and looked at modern strain gauges. Sensor Technology’s new SGR series torque sensors use a
four-element diamond formation strain gauge or Wheatstone bridge, connected to a miniature shaft-mounted analog-to-digital converter and microcontroller. When the shaft rotates two gauges go into tension and two into compression. The microcontroller, mounted as close to the gauges as possible to minimise external noise pick-up, measures these levels and creates a real-time digital data stream. This is transferred wirelessly from the rotating shaft to a second static microcontroller which performs calibration and temperature
15
compensation to produce an accurate torque reading. The new bridge-based sensors are robust, reliable, highly accurate,
and easy to use. Introduced at the end of 2019, they have already created considerable interest amongst users and are fast becoming best sellers. From a standing start 50 years ago, real time torque measurement
has grown and grown. Instead of plateauing, demand has expanded as plant and machinery design has developed. Today, operators need their machines to run at top performance, and use the power of modern computers to constantly assess and reassess all dynamic parameters so that optimised running can be ensured at all times. Naturally these computers need real-time feedback data, principal among which is torque data from the drive systems. Fifty ago Sensor Technology
was building torque sensors for machines that now seem somewhat run of the mill. Today, it is at the current edge of all the developing technologies – from green energy generation to electric, fuel efficient and driverless cars; flood control, irrigation and water management; precision engineering, manufacturing and assembly; medical, surgical and healthcare
automation; marine and aerospace propulsion systems. To express it statistically, the world’s population of rotating shafts is growing exponentially, and Sensor Technology has to keep up.
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