A race car generates a lot of electro-magnetic noise from
the ignition and telemetry systems. This means that there
must be minimal wiring length between the strain gauges
and the amplifiers. Secondly, to provide representative
data, the weight of the whole system must not alter the
dynamics of the car.
2006 BMW 320si WTCC
Integrated strain gauges in the gearshift lever trigger a power signal.
Strain Gauging is a form of load sensing.
Parts are instrumented with a very thin metallic foil.
A strain gauge consists of a thin metallic filament (wire) arranged in a pattern on top
of a foil which is bonded (glued) to a part. As an example the part may be a
suspension pushrod from a formula car. As the part deforms under load, the filament
is microscopically stretched in length and because of this there is a change in its
electrical resistance. When the circuit is active (powered), such change in resistance
causes a small voltage change. This can be amplified and calibrated on a rig so that
for a given load (deformation) the voltage is known.
In motorsport, amplifiers are mostly non-ratiometric whereby the supply voltage does
not (within reason) affect the reading, until the voltage is too low or high for the
gauge to actually function properly. This allows data to be compared easily. Some
applications may however have a ratiometric amplifier if the software then uses a
reference rail voltage to calculate the corrected gauge reading. The latter method is in
a way more versatile and has slightly simpler circuitry.