MTS Series 793 - Manual (Page 93)

How to Perform Advanced Tuning Techniques
MTS Series 793 Tuning and Calibration Tuning Procedures 93
How to Manually Tune Three-Stage Servovalves
Note For FlexTest SE Controllers, this procedure requires the optional Scope,
or an external oscilloscope.
Note This section applies only to systems using three-stage servovalves such
as the Model 497.15 or 493.15 Servovalve.
About the inner loop Systems equipped three-stage servovalves have an inner control loop inside the
test system’s primary, or outer control loop.
The inner loop, like the outer loop, has gain and rate controls that can be adjusted
to optimize performance. The inner-loop is tuned at system installation, and
requires periodic fine tuning when the outer-loop becomes sluggish.
The inner loop is similar to a displacement control mode for the outer-loop.
Three-Stage Valve Driver modules include the electronics necessary to support
the inner control loop.
Important Always tune the inner loop without the hydraulics applied to the
actuator. Perform the inner loop gain adjustments with hydraulic
pressure removed from the main spool while maintaining pressure
at the pilot stage. This prevents interaction between the inner and
outer loops.
Prerequisites • The hydraulic fluid and the servovalve should be at operating temperature.
See
“When to Tune” on page 49.
• Command compensators should be turned off.
• The specimen should be removed.
Program
Command
Control
Signal
Inner
Loop
Outer
Loop
HSM
Hydraulic
Power
Supply
493.15 Valve
Driver
Feedback
The innerloop
(proportional) gain and rate
(derivative) adjustments
are the same types of
adjustments as the
proportional and derivative
gain adjustments of the
outerloop tuning controls.