A control system for a chemical concentration control system is shown in Figure P9.11. The system receives a granular feed of varying composition, and we want to maintain a constant composition of the output mixture by adjusting the feed-flow valve. The transfer function of the tank and output valve is
and that of the controller is
The transport of the feed along the conveyor requires a transport (or delay) time, T = 1.5 s. (a) Sketch the Bode diagram when K1 = K2 = 1, and investigate the stability of the system, (b) Sketch the Bode diagram when K1 = 0.1 and K2 = 0.04, and investigate the stability of the system, (c) When K1 = 0, use the Nyquist criterion to calculate the maximum allowable gain K2 for the system to remain stable.
