B$-4-2.$ Consider the liquid$-$level control system shown in Figure $4-43.$ The controller is of the proportional type. The set point of the controller is fixed.

Draw a block diagram of the system, assuming that changes in the variables are small. Obtain the transfer function between the level of the second tank and the disturbance input $q_d.$ Obtain the steady$-$state error when the disturbance $q_d$ is a unit$-$step function.

Liquid$-$level control system.