CBE 491 (CBE 433) Review II: Fall 2012

Controller Block Feedback Control Loop measure some property compare to setpoint decide what to do change another property Loads Flowrate Temp or Level Process Action Measure Feedback Control Loop error Decision Compare SP

Controller Block c(t) = CV or PV or TO m error c Decision Compare SP m c e = r - c (-) Control algorithm (+) r m = output of controller (MV or CO)

Control Algorithms 1. ON/OFF Control Direct controller (ac = +1) If e > 0 Then m = 0% If e < 0 Then m = 100% OFF ON Reverse controller (ac = -1) If e > 0 Then m = 100% If e < 0 Then m = 0% ON OFF

Example: P Control Loop on BZ Flash aT = +1 AC aC = -1 av = -1 aP = -1 Reverse controller (ac = -1) If e > 0 Then m = 100% If e < 0 Then m = 0%

Example: P Control Loop on BZ Flash aT = +1 AC aC = +1 av = -1 aP = -1 What IF: Direct controller (ac = +1) If e > 0 Then m = 0% If e < 0 Then m = 100%

Example: Graph Signals Pressure = c r - c = e 100% m m 0% 100% Flow  VP 0% t

On / Off Control Okay for Some Systems

P & PI Algorithms: Open & Closed Loop Responses OPEN LOOP: analysis of controller …. Only CLOSED LOOP: analysis of controller …. In the control loop P-Only t c r r - c = e m Flow (qo) 100% 0% qi OPEN LOOP

P & PI Algorithms: Open & Closed Loop Responses OPEN LOOP: analysis of controller …. Only CLOSED LOOP: analysis of controller …. In the control loop P-Only t c r r - c = e m Flow (qo) 100% 0% qi CLOSED LOOP

P & PI Algorithms: Open & Closed Loop Responses Proportional & Integral PI t c r r - c = e m Flow (qo) 100% 0% qi OPEN LOOP

P & PI Algorithms: Open & Closed Loop Responses Proportional & Integral PI t c r r - c = e m Flow (qo) 100% 0% qi CLOSED LOOP

Problem solving exercises Homework