MTS Series 793 - Manual (Page 36)

MTS Series 793 Tuning and Calibration
About Tuning
Introduction 36
Ramp and tapered ramp
waveform
A ramp waveform (also called a triangle waveform) requires the actuator to move
at a constant rate. This requires the servovalve to move quickly between two
discrete openings. Cycling a ramp waveform produces a triangle waveform.
Tapered ramp waves taper from 0% to 100% amplitude at the beginning of
execution, and from 100% to 0% at the end of execution.
• A ramp waveform is useful for all levels of tuning.
• Use a ramp waveform if a square waveform creates excessive velocities or
acceleration for the type of specimen being tested.
• Monitor the feedback or error signal to evaluate the system stability.
Sine and tapered sine
waveform
A sine waveform (also called sinusoidal or haversine) requires the servovalve to
move at a variety of rates.
Tapered sine waves taper from 0% to 100% amplitude at the beginning of
execution, and from 100% to 0% at the end of execution.
Random function
generator
When tuning AIC compensator configurations, it is necessary to generate random
functions to properly simulate typical test conditions.
Random functions employ a pre-emphasis filter to make the convergence rate
constant over all frequencies. The random function options include:
• Random - 1/F
2
• Random - 1/F
• Random - Flat (none)
• Random - F
• Random - F
2
Frequency
A low-frequency waveform is adequate for most testing. Tests at higher
frequencies cause a frequency shift that cannot be completely corrected with the
PIDF adjustments.
• Do your initial tuning at a low frequency, and then fine tune at the highest
frequency in your test program. Common values are
1–2 Hz.
• Servo adjustments that do not improve performance at high frequencies
generally indicate that the servovalve is running at 100% capacity or the
HPU is running at 100% capacity.