Two basic ways to look at the BEHAVIOR OF YOUR SYSTEM (i.e. its 'Response').
There are two 'domains':
Time Domain
Frequency Domain
...and there are two corresponding ways to plot response:
Transient Response is the same thing as "step response"
- You make an abrupt change to the INPUT and watch the response of the OUTPUT over TIME.
Frequency Response is typically shown using a "Bode plot"
- You use a sinusoidally-varying INPUT signal at some particular frequency.
- You determine the GAIN (also called magnitude), which is the ratio of OUTPUT/INPUT sine wave amplitude.
- You determine the PHASE (typically in DEGREES) from the INPUT to the OUTPUT sine wave.
FYI: If a problem states, "make Bode plots (magnitude and phase vs. frequency) of the steady-state response of the system output to a sinusoidally-varying input," it is providing redundant information:
A Bode plot IS (by definition) a plot of the steady-state response of system output to a sine wave input.
Note that a Bode plot can be made using either:
a theoretical model of the system (e.g. your state equations
and/or transfer function of a system) [This is what we do in class and
on problem sets...]
some empirical measurements (i.e. you excite the system at a
particular frequency, wait until the response has time to 'settle' into
stead state, measure gain and phase, and then repeat this process for a
variety of discrete frequencies... You would typically do this as a
reality check on your model, to find the actual response of a system.)
