MTS Landmark Tabletop - Manual (Page 105)

2. Turn on electrical and hydraulic system power.
3. Apply low hydraulic pressure to the servovalve so that hydraulic fluid gradually fills the filter cavity.
4. Apply high hydraulic pressure and check for leaks.
Adjusting the Mechanical Null
This procedure describes how to adjust the mechanical null for the Series 252 Servovalve. The mechanical
null adjustment aligns the servovalve spool to a position that allows little or no actuator movement when there
is no control signal.
Prerequisites
Read this procedure before attempting to adjust the mechanical null. The mechanical null adjustment is quite
sensitive, and you should be familiar with the hazards that can be encountered when performing the procedure.
Perform the servovalve mechanical null adjustment after the valve balancing procedure (electrical
compensation) has been completed and the results are judged unsatisfactory.
During the servovalve mechanical null adjustment procedure, the actuator must be able to move through full
displacement in either direction without contacting a reaction surface.
Valve Balance Adjustments
MTS controllers have an electronic mechanical null adjustment called valve balance. The valve balance
adjustment is a convenient way to compensate for a servovalve that needs a mechanical null adjustment.
The adjustment introduces an electrical offset signal that causes the servovalve to hold the position of the
actuator when a zero command is issued.
Adjust the Mechanical Null
Warning:
Sudden and unexpected actuator rod movement can cause serious injury to personnel and/or
damage to equipment.
Do not perform the following procedure without clearing the path of motion of the actuator.
Ensure that all personnel, specimen/structures, and tools are away from the path of motion of
the actuator (crush zone).
1. Exercise the actuator.
The actuator should be exercised to warm it up. Electrical and mechanical adjustments are more repeatable
after the actuator is warmed up.
a) Select displacement control for the controller.
b) Disable the reset integrator or adjust the Reset control for zero.
c) Adjust the actuator for mid-displacement.
d) Turn on electrical and hydraulic system power.
MTS Landmark™ Tabletop Load Units Product Information 105
Maintenance