MTS Acumen - Manual (Page 170)

Tune for Specimen Element
When you choose an existing tuning set or select the auto tune feature, you typically do so in the stable
displacement control mode (best practice). The tuning set you select or generate (with the auto tune
feature) determines tuning values for control modes used for testing, such as force and displacement.
The verify feature applies the tuning values to the control modes you specify (that is, displacement or force
testing control modes, not stable displacement) to validate their effect on the servo loop.
Warning :
When force is the active control mode and the actuator is decoupled from the specimen, the
system may become unstable, causing unexpected actuator movement and possible injury
to anyone in its path.
Never select force as the active control mode unless you have tuned your system to your
specimen and fixture, and have validated the stability of the force control mode.
It is best practice to perform all fixture and specimen installation in the stable displacement
control mode.
Interpretation of Results
In most cases, optimal results are achieved when the pointer is positioned in the center of the green zone.
If the loop is under-tuned, or tuned to under-perform and become sluggish (also referred to as “tuned
cold”), the pointer will be positioned to the left in the blue zone. If the loop is over-tuned, or tuned to
170 | MTS Acumen ™
Best Practices for Other System Configurations and Tests