▁at ten u ation ▁of ▁the ▁external ▁disturb ance . ▁The ▁sens itivity ▁function ▁tells ▁us ▁how ▁the ▁dist urban ces ▁are ▁influenced ▁by ▁feedback . ▁Dist urban ces ▁with ▁frequencies ▁such ▁that ▁ ▁is ▁less ▁than ▁one ▁are ▁reduced ▁by ▁an ▁amount ▁equal ▁to ▁the ▁distance ▁to ▁the ▁critical ▁point ▁ ▁and ▁dist urban ces ▁with ▁frequencies ▁such ▁that ▁ ▁is ▁larger ▁than ▁one ▁are ▁ampl ified ▁by ▁the ▁feedback . ▁ ▁It ▁is ▁important ▁that ▁the ▁largest ▁value ▁of ▁the ▁sens itivity ▁function ▁be ▁limited ▁for ▁a ▁control ▁system ▁and ▁it ▁is ▁common ▁to ▁require ▁that ▁the ▁maximum ▁value ▁of ▁the ▁sens itivity ▁function , ▁, ▁be ▁in ▁a ▁range ▁of ▁ 1 . 3 ▁to ▁ 2 . ▁ ▁S ens itivity ▁Circle ▁The ▁quantity ▁ ▁is ▁the ▁inverse ▁of ▁the ▁short est ▁distance ▁from ▁the ▁Ny qu ist ▁curve ▁of ▁the ▁loop ▁transfer ▁function ▁to ▁the ▁critical ▁point ▁. ▁A ▁sens itivity ▁ ▁guarante es ▁that ▁the ▁distance ▁from ▁the ▁critical ▁point ▁to ▁the ▁Ny qu ist ▁curve ▁is ▁always ▁greater ▁than ▁ ▁and ▁the ▁Ny qu ist ▁curve ▁of ▁the ▁loop ▁transfer ▁function ▁is ▁always ▁outside ▁a ▁circle ▁around ▁the ▁critical ▁point ▁ ▁with ▁the ▁radius ▁, ▁known ▁as ▁the ▁sens itivity ▁circle . ▁ ▁defines ▁the ▁maximum ▁value ▁of ▁the ▁sens itivity ▁function ▁and ▁the ▁inverse ▁of ▁ ▁gives ▁you ▁the ▁short est ▁distance ▁from ▁the ▁open - loop ▁transfer ▁function ▁ ▁to ▁the ▁critical ▁point ▁. ▁ ▁References ▁ ▁See ▁also ▁ ▁Rob ust ▁control ▁