12.5. Polar Grid Lines in Root Locus Diagram
The damping ratio is used to determine the angular location of the poles while the undamped natural frequency wn gives the distance of the pole from origin. Both the damping ratio z and natural frequency wn can be shown on the root locus diagrams. The damping ratios are indicated by straight lines passing through the origin whereas natural frequencies are indicated by circles for their different values, respectively.
In MATLAB, constant damping ratio and natural frequency grid lines can be drawn in a root locus plot by using the following command(s):
| sgrid | Plots the grid lines of constant damping ratio z from 0 to 1 with an increment of 0.1 and circles of constant natural frequency wn. |
| sgrid(z, wn) ... |
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