Re: Bode diagrams ?
If a system will always operate in closed-loop then you will want the bode plot of the closed-loop system, however there are cases where the closed-loop system is used a benchmark for the open-loop system. An example of this is when you add compensators to a system to correct gain or phase margin of the open-loop system, but want to maintain a certain "closed-loop" steady state error, this allows you to adjust gain of the closed-loop system to match the specification, but the system itself operates in open-loop or is only one component of a larger system which may or may not be closed.
You can learn information from the open-loop bode plot about how the closed-loop system.
- Jayson