Which plot of cotrol system is accurate and absolute ?

Hi,
I am interested to know,

which plot(Ny, Bode, Nichols, RH, etc) of control systems will be more accurate and absolute in describing stability (Open loop and for closed loop if compensator is added) of a system and why .......?

or else

Provide me source of information ?

Thanking you[/color]

manju_nath200 said:

Hi,
I am interested to know,
which plot(Ny, Bode, Nichols, RH, etc) of control systems will be more accurate and absolute in describing stability (Open loop and for closed loop if compensator is added) of a system and why .......?

Click to expand...

*All plots are (resp. can be) "accurate".
*However, if you are interested in stability issues, the Nyquist plot of the loop gain is the most universal one, since you can check stability for all kinds of system.
From the BODE plot, for example, you can derive stability information only if the "simplified Nyquist criterion" is applicable (opwn loop stable, no poles in the RHP, only one crossing point for the loop gain magnitude (0 dB) and phase (180deg) response.

Added after 45 minutes:

Supplement to the above:

The remarks concerning the BODE plot concern only the derivation of the phase resp. gain margin.
As the BODE plot contains all the information from the Nyquist plot (only different in the graphical representation) you can derive all stability issues (yes/not) also from the BODE plot - but, for my opinion, it is somewhat more complicated (counting of the axis crossings for each direction).