is the angle associated with the radial load.
With
,
it is easy to see that P will result in equal strain showing up on all four
gauges, so that the bridge output will remain unaffected. However, as
approaches
,
we can see that the flexure with the strain gauges will be loaded in the same
way a torque loads the flexure. Using the method described in 4.2.2, with a
different load and different area moment we find an equation that relates
radial forces in the
direction to output voltage in the strain gauge circuitry :
|
(39) |
where h and w are the height and width of the flexure elements, L is the length of the damper, and l is the length of the strain gauge. Substituting our approximation for radial forces (38), we obtain output voltage due to radial forces as a function of damper velocity.
|
(40) |
Comparing this result to (28), which related damper velocity to output voltage due to damping torque, we can make an approximation of the signal to noise ratio of our sensor :
|
(41) |
where l is the length of the strain gauge, L and R are the length and radius of
the damper, t is the flexure thickness, and
is the non-dimensionalized damper eccentricity. If we assume the misalignment
of the damper cup is 0.003", the gap size is 0.015" (these are reasonable
values), we obtain a signal to noise ratio of 3.3. Clearly, this result is
unacceptable if we intend to use this sensor to measure damper torque. In
4.2.5, we outline two design modifications that will improve the signal/noise
ratio remarkably.
