IV.2.1 Closed loop response of liquid level in a storage tank: A case study

Fig IV.7 represents the closed loop block diagram of a storage tank whose liquid level needs to be controlled at a predefined setpoint.

Fig. IV.7: Schematic of closed loop block diagram of storage tank

We analyze various components of the above,

Process : The process has two inputs and one output. Input can be manipulated whereas input is the source of disturbance. Output varies proportionally with the square root of the height of the liquid in the tank as, The material balance around the tank gives the following model,

(IV.18)