Owner's manual

Series 322 Load Unit Maintenance

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.

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.

E. Define a 50%, 0.1 Hz sine wave command and allow the actuator to

warm up for approximately one-half hour.

F. After the warmup period, stop the test program.

2. Check for actuator movement.

This task is a test to determine how to proceed.

Disconnect the servovalve cable and observe the actuator rod.

• If the actuator rod has no noticeable movement, the servovalve is at the

null position and does not need to be adjusted. Proceed to Step 4.

• If the actuator rod noticeably moves, the servovalve requires

adjustment. Proceed to Step 3.

3. Set the adjuster pin.

This task describes the mechanical null adjustment procedure.

A. Insert a 3/32-inch hex key into the adjustor pin socket. See the

following figure for the location of the adjustor pin.

WARNING