MTS Landmark Floor Standing - Manual (Page 34)

69 MPa (10,000 psi) to accommodate a variety of grips manufactured by MTS Systems Corporation. A front
panel control allows the grip pressure to be adjusted within the factory setting. A rate control sets how fast
the grips open and close.
Actuator velocity limiting switch
This switch/indicator is used to control actuator speed. The switch is spring loaded left/right with a center
neutral position. Momentarily turn the switch right to the hare and then return the switch to the center position
for high-speed, normal testing operation. The switch indicator will light, indicating the actuator rod is capable
of high-speed, normal testing operation. Momentarily turn the switch left to the tortoise and then return the
switch to the center position for low-speed specimen installation and removal. The switch indicator will
extinguish, indicating the actuator rod is in a low speed condition for specimen installation.
Integrated actuator assembly
The integral actuator beam includes the hydraulic service manifold (HSM) that acts as the hydraulic interface
between the HPU and the components that comprise the actuator beam [actuator, servovalve(s), and
accumulators] of the load unit. It contains the required hydraulic porting and piping to accommodate the
hydraulic components. The HSM and the actuator speed control also controls the hydraulic pressure to the
load unit.
• Actuator: The actuator can be located in the middle of the load unit base or crosshead. It is a hydraulically
powered piston that applies displacement of (or force into) a specimen. It can apply equal power in tension
and compression. One end of the test specimen is installed into a fixture which is mounted to the end of
the actuator rod.
• Servovalve(s): The servovalve(s) regulates the direction and flow of the hydraulic fluid to and from a
hydraulic actuator. The servovalve responds to the polarity and magnitude of the command signal generated
by the controller.
• Accumulators: The accumulators suppress line-pressure fluctuations. The load unit includes a pressure-line
accumulator to provide fluid storage so a constant line pressure can be maintained at the servovalves for
maximum performance. The return-line accumulator minimizes return-line pressure fluctuations.
• Pressure Control: The load unit can be configured for several pressure configurations. The free flow
configuration passes the hydraulic pressure from the HPU (or hydraulic service manifold) through the
manifold to the hydraulic components. The hydraulic pressure options include on/off control, high/low/off
control, and high/low/off control with a proportional valve to ramp the pressure transitions.
Transducers
The load unit includes a force transducer and an LVDT.
• Force: The force transducer (also called load cell or force sensor) measures the amount of tension or
compression and rotational torque applied to it. It has four strain gages that form a balanced Wheatstone
bridge. When forces are applied to the bridge, it becomes unbalanced and produces an electrical signal
that is proportional to the force applied to it. The force transducer is a resistive device and requires a DC
conditioner to process the axial signal from the Wheatstone bridge.
• LVDT: The LVDT measures the linear actuator’s travel. The LVDT consists of a transformer with one
primary and two secondary coils wound on a common cylinder. The coil is stationary inside the actuator.
A core is attached to the piston rod of the actuator. As it moves inside the coil, it produces an electrical
signal that represents the position of the piston rod. The phase of the signal indicates the direction the
actuator rod is moving. An LVDT requires an AC conditioner to process the signal.
34 MTS Landmark™ Floor Standing Load Units Product Information
Introduction