In the early 1990s, news leaked out that Sensor Technology was developing
a low cost torque sensor based on surface acoustic wave (SAW) technology
as part of a DTI LINK scheme. The technology showed much early promise,
with a prime example of its potential demonstrated in its use in the
development of an all-electric power steering system, developed for small
'city' cars, where the use of heavy, bulky hydraulic power steering would
have been impractical.
Now, with the arrival of Torqsense transducers, Sensor Technology has
launched a 21st Century solution to the problem of rotary torque
measurement with a range of products that are finding uses in a diverse
spread of applications. In particular, the SAW technology opens up new
application areas where knowledge of torque is critical.
Rotary torque has historically been difficult and expensive to measure
because traditional techniques are invasive to the mechanical systems
being measured. Torqsense overcomes these problems by using SAW
technology in a novel way. The SAW transducer is essentially a 'frequency
dependent' strain gauge that measures the change in resonant frequency
caused by an applied shaft strain.
Two SAW devices embedded on a shaft form part of a high frequency
oscillator circuit. When the shaft is twisted, the resulting deformation
of the substrate creates a frequency difference between the two devices,
which is a measure of the induced strain due to the twisting moment, and
from this the torque can be derived. The signals are obtained via
electromagnetic coupling, allowing non-contact, intrinsically safe torque
measurement.
Key characteristics of the SAW based transducer include a resolution to
one part in ten million, an extremely linear response (better than 0.1%)
and a bandwidth in the order of 1MHz.