A brief history of the Strain Gauge
Lord Kelvin first reported on a relationship between strain and the resistance
of wire conductors.
Charles Kearns made the first notable use of bonded resistance strain gauges
to measure vibratory strains in high performance propeller blades.
He used carbon composite resistors (as used in standard electronic instruments)
ground flat and mounted on an insulating strip. These were then cemented onto
the propeller blades, and were able to indicate the dynamic strains experienced
by the blades. However, these gauges were not very accurate, and due to the
resistance stability with variations in time and temperature being poor, the gauges
were unable to measure slowly changing or static strains.
Arthur Ruge and Edward Simmons (working independently of each other) both
discovered that small diameter wires made of electrical resistance alloys could
be bonded to a structure to measure surface strain.
This type of gauge had the advantage of responding well to static strains.
Following this break through, strain gauge measurements were adopted for
use in aircraft development programmes during World War II.
It was due to the demands of this rapidly growing industry that the important
advance into foil strain gauges was made.
The Saunders-Roe Company (UK) were seeking improvements in the performance
of the bonded wire gauges to enable their use in more demanding environments.
At this time, printed circuits were emerging, and Saunders-Roe developed the
idea of making a strain gauge by etching the pattern for the gauge from a thin
foil. These foil gauges had some distinct advantages, most notably a reduction in
size and production costs.
This allowed much more extensive use of electrical resistance strain gauges, and
they are the most common type in use today.
Semiconductor strain gauges are also in use today, and these differ in many
aspects from the metallic wire and foil strain gauges. Most importantly, they
produce much greater sensitivity (10 to 50 times), which was at one time thought
to herald the downfall of metallic gauges. But, semiconductor gauges are very
limited as a general purpose gauge, and so there is a place for both types in
modern strain measurement.
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