Do we use closed loop or open loop information in Bode plot, Nyquist plot and Root Locus?

1. Is Bode plot for open-loop or closed-loop?
2. Why Bode plot is drawn for open-loop transfer function?
3. Is a root locus plot created from the open-loop or closed loop transfer function?
4. What is the difference between a root locus plot and a Bode plot?

Is Bode plot for open-loop or closed-loop?

Bode plots show us magnitude and phase, but only for an open loop transfer function KG(s) evaluated at s=jω, 0<ω<∞, whereas the root locus, using some open loop L(s), shows the complex trajectory of closed loop poles when ranging some parameter K∈(0,+∞).

Why Bode plot is drawn for open-loop transfer function?

The Bode plot for the open-loop transfer function, i.e. G(s)H(s), gives a convenient way to determine the above parameters and hence the stability of a system. An open-loop gain of 1 is, on the log scale of dB, a gain of 20 lg 1=0 dB.

Is a root locus plot created from the open-loop or closed loop transfer function?

– The Root Locus Plot is a plot of the roots of the characteristic equation of the closed-loop system for all values of a system parameter, usually the gain; however, any other variable of the open- loop transfer function may be used.

What is the difference between a root locus plot and a Bode plot?

Bode plots show the gain-phase relationship with frequency directly and are most useful for compensating fixed-gain amplifiers. Root-locus plots show the closed-loop poles in the s-plane and how these poles vary with loop gain.