The motion of the lower sample grip is
produced by the hydraulic actuator and
servo-valve shown opposite.

Hydraulic fluid is provided by a 20 L/min pump,
and is maintained at a suitable temperature by
a water-cooled heat exchanger.

The servo-valve is controlled by a closed-loop
digital controller, which may use actuator
position, applied load, or sample strain as the
control parameter.

The waveform or ramp required for the test may be programmed on the control panel, or in the "MAX" software of the control computer.

The frequency response of the system is determined by the hydraulic pump output, the amplitude of the actuator motion, and the load applied to the sample.