MTS Model 286-30 Pore Pressure Intensifier - Manual (Page 25)

Pore Pressure System Operation Considerations
286.30 Pressure Intensifier Operation 25
Typical Calibration of Control Parameters
The two control parameters, pressure and volumetric displacement (unlike the
force parameter in axial testing, which usually has both tensile and compressive
force directions or polarities) are uni-directional. Positive commands applied to
the electronic controller equipment will cause pressure or volumetric
displacement (depending on which parameter is being controlled) to increase to
some positive level above zero.
For example, to cause pressure to increase from zero to full scale, you would
adjust the command input to the controller to +100%.
Applying a negative command at the controller, in either control mode (see
“Closed-loop Control Modes Used for Pressurizing Pore Fluid” on page 24 for
definition of “control mode”) would cause the piston rod of the pressure
intensifier to fully retract. While testing, negative commands have no practical
use and can cause the error detectors (see
“Use of Error Detectors and Limit
Detectors While Pressurizing” on page 27) to trip because neither controllable
variable can go negative. However, during certain pretest operations, such as
when causing the pressure intensifier to stroke to its low end or starting position,
negative commands are used.