16-08-2012, 03:59 PM
Mass Moment of Inertia,
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Mass Moment of Inertia
Inertia, as defined by Newton’s Laws of Motion, is
a body's (mass) resistance to a change in
momentum, whether in motion or at rest. The
intrusion of a torque-sensing device into the
testing driveline, therefore, adds an element of
mass to the test system. This changes the dynamic
characteristics of the drive system under test. In
the static state, this intrusion is effectively nulled
out by virtue of the relationship:
Torsional Stiffness
Strain gage torque sensors deform linearly under
load. This deformation, called strain (ε ), is
important to the successful measurement of torque.
In a dynamic rotating system, the stiffer the
rotating member is, the more faithful the
measurement of torque will be.
Shaft Criticals
At specific rotational speeds of the shaft of a
rotating torque sensor will, under certain
conditions of loading and support, become
dynamically unstable due to shaft resonance. If the
condition of instability is maintained, mechanical
failure can occur. Shaft criticals will occur at more
than one speed, but generally the first order
harmonic, or the lowest speed at which resonance
occurs, is the one most engineers are interested in.
A good general rule to follow is that the rotating
speed of the system should always be at least ten
percent above or below the rotating torque sensor's
shaft critical. When passing through a shaft
cr it ical, ti me of passage is recom mended to be as
shor t as possible to pr event potenti al system
damage.
Conclusion
SensorData Rotating Transformer Coupled Torque
Sensors are designed with all the previous
considerations in mind. Low mass, short length,
and minimal outside diameter directly translate to
greatly reduced mass moment of inertia, enhanced
torsional stiffness, and higher shaft criticals.