MTS Series 244 Actuators - Manual (Page 19)

• Material test systems usually mount the actuator in a load unit assembly. The actuator can be mounted
below the base plate or above the crosshead. The end of the actuator uses fixtures (such as grips) to
attach the test specimen to it.
Actuator Operation
Actuator piston rod movement is accomplished by supplying high- pressure hydraulic fluid to one side of the
actuator piston and opening the other side to a return line. High-pressure hydraulic fluid is ported into the
cylinder through the retraction port or the extension port. The differential pressure across the piston forces
the piston rod to move. The amount of hydraulic fluid and the speed and direction of piston rod movement is
controlled by a servovalve.
If the piston rod contacts some external reaction point, then a force is applied to that point equal to the effective
piston area times the actuating pressure. The main criteria for selecting an actuator are the force and stroke
(displacement) required for the job.
LVDT Operation
The internally mounted LVDT (linear variable differential transformer) provides an indication of the actuator
piston rod displacement.
Series 244 Actuators Product Information 19
Introduction