P9.11 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 transport of the feed along the conveyor re

quires a transport (or delay) time, T = 1.5 s. (a)

Sketch the Bode plot when K K 1 2 = = 1, and inves

tigate the stability of the system.

(b) Sketch the Bode plot 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 allow

able gain K2 for the system to remain stable.

FIGURE P9.11 Chemical concentration control. Feed Controller Ge(s) Desired concentration ooooooo Conveyor Measurement of concentration Controller Conveyor Tank 5 Y(s) R(s) S 5s+1 Composition