Advanced System Settings Dialogue - CellScale BioTester User Manual

Advanced System Settings Dialogue

Advanced settings are available by selecting Advanced from the Settings menu. All of these
settings are template specific.
True Strain Rate
Unlike nominal or engineering strain rate,
a plot of velocity versus time for a true
strain rate test would be non-linear. The
degree of non-linearity increases with
increasing strain.
approximates this non-linear curve with a
series of linear segments. Typically, 10
line segments is a sufficiently close
approximation. More segments can be
used, but you should bear in mind that the
actuator velocity can only be updated
every 250ms.
Data Averaging
The load cells are sampled at 100Hz with
hardware using a central moving average
of 8 samples. Further data averaging can
be applied to further smooth noisy data.
Force Control Settings
Force Control Settings affect the rate and
stability at which forces are achieved. These
settings apply to preloading as well as Force
Control Modes.
Kx and Ky (Default = 100, integer values) are proportional gain tuning parameters (one for
each of the coordinate axes). They control the sensitivity or the amount of corrective action
that is applied to the difference between the current and target force values. At low gain
values the system may be safe and stable but may be sluggish in response to changing
conditions. If the proportional gain is increased the system becomes more responsive and
loads are achieved more quickly. If Kx and Ky are set too high, an unstable oscillating
system may result and forces may never be achieved. The optimal value for these settings
depends on the properties of the material being testing. For stiff tissues, values may range
between 1 and 10. For soft tissues values may range between 50 and 200. Kx and Ky
usually are set equal to each other unless testing materials are strongly anisotropic.
Tolerance (mN) (Default = 3) controls how close to the specified force the actual load values
need to be. For example, a specified force of 100 mN with a Tolerance of 3 mN will be
considered achieved when the loads are between 97 and 103 mN.
tolerance of the load cell being used when choosing the value for this parameter. The load
cells typically fluctuate by about 0.1% of their full scale during the course of a test. For a
1000mN load cell this is about 1mN but for a 23N load cell, this is about 23mN. This value
should usually be 0.2-0.5% of full scale to ensure stable operation.
Settling Frames (Default = 5) controls how many successive load samples (sampled at 100
Hz) need to be within the Tolerance criteria for the force to be considered achieved. For
example, a specified force of 100 mN with a Tolerance of 3 mN and Settling Frames = 5 will
be considered achieved when the loads are between 97 and 103 mN for 5 successive data
samples.
The BioTester
BioTester User Manual
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