ADLINK PCI-8258 - Manual (Page 107)

Motion Control Theory 93
PCI-8254 / PCI-8258
4.2.5 Bode Plot
4.2.5.1 Structure Overview
The Bode Plot tool provided by your PCI-8254/8258 may display
transfer function's frequency responses of Linear Time-Invariant
(LTI)system. In general the X-axis of a Bode plot indicates
frequency in Log scale while its Y-axis Gain and Phase.
Expressed in unit of (dB), gaining is the level of enlargement and
contraction between input and output signals. Expressed in unit of
(Degree), phase is the leading or trailing extent between input and
output signals. You may learn about system features including
stability and resonance point with the Bode plot's frequency
response function. This may help users in determining system's
compliance with given requirements and provide advanced users
with important system features including system transfer function's
order, pole, and zero points. This offers great assistance in system
identification and advanced controller design.
The PCI-8254/8258 system's fully-closed circuit feature can
estimate frequency response in varieties format safely and more
accurately. See figure below for overall structure where
continuous sine wave input signals are generated with fixed
amplitude and frequency. You may retrieve servo motor's position
feedback signal (encoder) to analyze close-loop system's
frequency response performance, including PID controller,
feedforward control, filter, digital to analog conversion, driver, and
servo motor. This is a sine wave with changing amplitudes and
phases that you can use to get a group of closed-loop gain and
phase at specific frequency. This system's input signal is a motion
command and output signal the motor's feedback position. With
similar process we can get system frequency response in given
frequency range by increasing sine wave frequency. In addition,
the frequency response of Open-loop system and Plant is
provided. The plant's frequency response covers digital-analog
conversion, drive, and servo motor while the close-loop circuit
frequency response is the outcome of disabled feedforward
control, bypassed filter, and PID controller with plant. The signal
description table below describes meanings of signals captured at
different position of the structure diagram while the frequency
response type table outlines I/O signals under different system
frequency response.