The controller parameters are typically matched to the process characteristics and since the process may change, it is important that the controller parameters are chosen in such a way that the closed loop system is not sensitive to variations in process dynamics. One way to characterize sensitivity is through the nominal sensitivity peak, Ms.
The sensitivity function tells us how the disturbances are influenced by feedback. It is important that the largest value of the sensitivity function be limited for a control system and it is common to require that the maximum value of the sensitivity function, Ms, be in a range of 1.3 to 2.
