Presentation on theme: "Dynamic Behavior of Ideal Systems"— Presentation transcript:
1Dynamic Behavior of Ideal Systems Chapter 6Dynamic Behavior of Ideal Systems
2Overall Course Objectives Develop the skills necessary to function as an industrial process control engineer.SkillsTuning loopsControl loop designControl loop troubleshootingCommand of the terminologyFundamental understandingProcess dynamicsFeedback control
3Ideal Dynamic Behavior Idealized dynamic behavior can be effectively used to qualitatively describe the behavior of industrial processes.Certain aspects of second order dynamics (e.g., decay ratio, settling time) are used as criteria for tuning feedback control loops.
7Determine the Process Gain and Process Time Constant from Gp(s)
8Estimate of First-Order Model from Process Response
9In-Class ExerciseBy observing a process, an operator indicates that an increase of 1,000 lb/h of feed (input) to a tank produces a 8% increase in a self-regulating tank level (output). In addition, when a change in the feed rate is made, it takes approximately 20 minutes for the full effect on the tank to be observed. Using this process information, develop a first-order model for this process.
10Second Order Process Differential equation Transfer function Note that the gain, time constant, and the damping factor define the dynamic behavior of 2nd order process.
15Characteristics of an Underdamped Response Rise timeOvershoot (B)Decay ratio (C/B)Settling or response timePeriod (T)
16Example of a 2nd Order Process The closed loop performance of a process with a PI controller can behave as a second order process.When the aggressiveness of the controller is very low, the response will be overdamped.As the aggressiveness of the controller is increased, the response will become underdamped.
17Determining the Parameters of a 2nd Order System from its Gp(s)
18Second-Order Model Parameters from Process Response
19High Order ProcessesThe larger n, the more sluggish the process response (i.e., the larger the effective deadtime)Transfer function:
20Example of Overdamped Process Distillation columns are made-up of a large number of trays stacked on top of each other.The order of the process is approximately equal to the number of trays in the column
21Integrating Processes In flow and out flow are set independent of levelNon-self-regulating processExample: Level in a tank.Transfer function:
22DeadtimeTransport delay from reactor to analyzer:Transfer function:
23FOPDT ModelHigh order processes are well represented by FOPDT models. As a result, FOPDT models do a better job of approximating industrial processes than other idealized dynamic models.
24Determining FOPDT Parameters Determine time to one-third of total change and time to two-thirds of total change after an input change.FOPDT parameters:
29Recycle Processes Recycle processes recycle mass and/or energy. Recycle results in larger time constants and larger process gains.Recycles (process integration) are used more today in order to improve the economics of process designs.
31Overview It is important to understand terms such as: Overdamped and underdamped responseDecay ratio and settling timeRectangular pulse and ramp inputFOPDT modelInverse acting processLead-Lag elementProcess integration and recycle processes