Exercise 5.8 Comparison of local feedback and cascade control Explain why a cascade control system with two measurements pH in each tank and only one manipulated input the base ow into the rst tank will not achieve as good performance as the control system in Figure  where we use local feedback with two manipulated inputs one for each tank 

Hint Show rst that the closedloop response for the cascade control system is as in

 but with L  GK L
 GG
KK
     Li 

i Yj

GjKj rather than Li  GiKi

The following exercise considers the use of buer tanks for reducing quality concentration
temperature disturbances in chemical processes