In a closed loop control system, the most valuable information for predicting system behavior/performane is to know the exact locations of the closed loop poles.  The root locus is a tool that lets you see how the closed loop poles change as you adjust the overall gain of the system.

• Why learn about the root locus?
• When you design a control system, the position of the closed loop poles in the s-plane determines system performance.  Performance measures like speed of response and overshoot are related to where the poles are.  It's the root locus that lets you see that information in a way that lets you see how things change when the gain changes.
• What should you know to learn about root locus?
• You need to be clear about how pole position is related to speed of response.
• You need to be clear about how pole position affects overshoot.
• What do you need to know about the root locus?
• You need to know the general rules for sketching the root locus.  If you know how the root locus behaves, then when you are designing a system you can use the root locus to help you understand the effects of adding various types of control or compensation to the system.
• How do you use the root locus in design?
• The root locus allows you to see pole locations as gain varies.  Here is an example of that.
• Problems
• Click here for Problems on the Root Locus
• Additional Information
• Click here for a set of links to various root locus calculators.

        Any lab problem that uses proportional control - or any PID controller - can be analyzed using root locus techniques.