For a liquid level control system similar to that in Figure 1 below, it has been argued that integral control action is not required because the process acts as integrator. 92 Figure 1. Liquid level control system with pump in exit line Tips to answer the question: 1 Assume that G,(s) = - and Ga(s) =- %3D As As Y Use the following equation for setpoint - Ysp 1+G,GyGp Gm Y Ga Use the following equation for disturbances D 1+GGyGp Gm For both setpoint and disturbance change determine lim y(t) = lim sY(s) for 00-S both y(t) and ysp (t) or Y(s) or Ygp (s) Afterwards determine whether the offset is eliminated or not by using: offset = Yp (t c0) Y(t - 0o0) or offset = Yp(s 0) Y(s - 0) %3D A During calculations and substitutions, T = - KKpKm Assume that the level transmitter and the control valve have negligible dynamics To evaluate this assertion, determine whether proportional only control will eliminate offset for step changes in: 1.1. Setpoint variable, and (13) 1.2. Disturbance variable. (7) roo