Practical Industrial Process Control: Understanding, Tuning & Autotuning Control Loops

1. Practical Industrial Process Control:Understanding, Tuning & Autotuning Control Loops Edi Leksono Department of Engineering Physics Institut Teknologi Bandung June 2003 Practical Industrial Process Control:Understanding, Tuning & Autotuning Control Loops Introduction to Process Control

2. GOALS Training Objectives • Introduction to process control • Elements of process control loop • Dynamic modelling • Analysis of dynamic systems • Design of P, PI, PD and PID for specific process objectives or product specifications • Design of feedback, feedforward, cascade, feedforward/feedback, feedforward/feedback + cascade controls • Tuning & Autotuning • Practical Troubleshooting Practical Industrial Process Control:Understanding, Tuning & Autotuning Control Loops Introduction to Process Control

3. + Controller Actuator Process Sensor + Transmitter Road Map of the Training • First, we will visit all the block elements of the control system,especially the controller • Then, analyze the whole system all together • Then, consider the variations of the elements Practical Industrial Process Control:Understanding, Tuning & Autotuning Control Loops Introduction to Process Control

4. Time Table Practical Industrial Process Control:Understanding, Tuning & Autotuning Control Loops Introduction to Process Control

5. Introduction to Process Control Edi Leksono Department of Engineering Physics Institut Teknologi Bandung June 2003 Introduction to Process Control

6. Session Outlines & Objectives Outlines • The importance of process control • Basic concepts of process control Objectives • Understand what process control is • Know the terms of process control system • Identify the elements of process control system • Understand the importance of process control • Know the type of process control strategies Introduction to Process Control

7. Energies Out Raw Materials Products Process Energies Out Definition (1) • Process • A series of interrelated actions which transform material It covers all resources that are involved in the process and talks about process “inputs” (e.g. resources, raw material) and “outputs” (e.g. finished product) • Control • To maintain desired conditions in a physical system by adjusting selected variables in the system Introduction to Process Control

8. Corrective Action Process Data Knowledge Information Definition (2) • Process Control • To maintain desired conditions in a physical system by adjusting selected variables in the system in spite of disturbances affecting the system and observation noise Introduction to Process Control

9. Brain: Control calculation Eyes: Sensor Steering wheel: Actuator Daylife Example: Driving a Car • Control Objective (Setpoint): • Maintain car in proper lane • Controlled variable: • Location on the road • Manipulated variable: • Orientation of the front wheels • Actuator: • Steering wheel • Sensor: • Driver’s eyes • Controller: • Driver • Disturbance: • Curve in road • Noise: • Rain, fog Introduction to Process Control

10. Product Stream TC Steam TT Feed Condensate Industrial Example #1: Heat Exchanger • Control Objective (Setpoint): • Maintain temperature • Controlled variable: • Outlet temperature of product stream • Manipulated variable: • Steam flow • Actuator: • Control valve on steam line • Sensor: • Thermocouple on product stream • Controller: • Temperature controller • Disturbance: • Changes in the inlet feed temperature • Noise: • Measurement noise Introduction to Process Control

11. Fluid LC LT Industrial Example #2: Liquid Level Control • Control Objective (Setpoint): • Maintain level • Controlled variable: • Fluid level in the tank • Manipulated variable: • Fluid flow • Actuator: • Control valve on fluid line • Sensor: • Level transmitter on the tank • Controller: • Level controller • Disturbance: • Changes in the inlet feed flow • Noise: • Measurement noise Introduction to Process Control

12. Elements of Process Control Loop • Sensor • Measure process variable • Transmitter • Convert the measured process variable into standard signal • Controller • Drive actuator by giving an appropriate controller output signal • Actuator • Adjust manipulated variable based on the value of the controller output signal • Process • Physical system to be controlled Introduction to Process Control

13. The Terms I • Control Objective (Setpoint, SP) • Controlled Variable (CV) or Process Variable (PV) • Measured Process Variable (PVm) • Controller Output (CO) • Manipulated Variable (MV) • Final Control Element (Actuator) • Sensor/Transmitter • Controller • Disturbance Variable (DV) • Measurement Noise Introduction to Process Control

14. 24 hours process operation? Hmm… I think, to achieve those, we need to continuously monitor & control the process 24 hours a day, 7 days a week!!! Goal of Process Operation • Safety & Reliability • Product Specification • Environmental Regulation • Operating Constraint • Efficiency • Maximum profit Introduction to Process Control

15. Safety and Reliability • The control system must provide safe operation • Alarms, safety constraint control, start-up and shutdown • A control system must be able to “absorb” a variety of disturbances and keep the process in a good operating region • Feed composition upsets, temporary loss of utilities (e.g., steam supply), day to night variation in the process Introduction to Process Control

16. New Controller Old Controller Product Specification • Quality • Products with reduced variability • For many cases, reduced variability products are in high demand and have high value added (e.g. feedstocks for polymers) • Product certification procedures (e.g., ISO 9000) are used to guarantee product quality and place a large emphasis on process control Introduction to Process Control

17. Environmental Regulation • Various government laws may specify that the temperatures, concentrations of chemicals, and flow rates of the effluents from a process be within certain limit Examples: • Regulations on the amounts of SO2 that a process can eject to the atmosphere, and on the quality of water returned to a river or a lake Introduction to Process Control

18. Operational Constraint • All real process have constrained inherent to their operation which should be satisfied throughout the operation Examples: • Tank should not overflow or go dry • Distillation column should not be flooded • Catalytic reactor temperature should not exceed an upper limit since the catalyst will be destroyed Introduction to Process Control

19. Efficiency • The operation of a process should be as economical as possible in utilization of raw material, energy and capital Introduction to Process Control

20. Maximizing the Profit of a Plant (1) • The operation of a process may many times involves controlling against constraints • The closer that you are able to operate to these constraints, the more profit you can make Example: • Maximizing the product production rate usually involving controlling the process against one or more process constraints Introduction to Process Control

21. Improved Performance New Controller Maximizing the Profit of a Plant (2) Constraint control example: A reactor temperature control • At excessively high temperatures the reactor will experience a temperature runaway and explode • But the higher the temperature the greater the product yield • Therefore, better reactor temperature control allows safe operation at a higher reactor temperature and thus more profit Introduction to Process Control

22. The History of Process Control • 1960s Pneumatic analog instrumentation, controllers, and computing modules • 1970s Electronic analog instrumentation, controllers, and computing modules • Direct digital control with special algorithms programmed in main frame computer • 1980s Electronic analog instrumentation and digital distributed control systems (DCS) • Supervisory and model predictive control configured in special purpose computers • 1990s Smart analog instrumentation, valves, and digital distributed control systems • Supervisory and model predictive control configured in special purpose computers • Neural networks, online diagnostics, and expert systems in special purpose computers • Real time optimization using model libraries in special purpose computers • 2000s Field bus based digital smart instrumentation, valves, and control systems • Digital bus takes full advantage of smartness and accuracy of instrumentation and valves • Some fast PID controllers such as flow and pressure go to the field transmitter or valve • Model predictive control, neural networks, online diagnostics, and expert systems are integrated into the graphically configurable field bus based control systems and move to PCs • APC Infrastructure, interface, and engineering costs decrease by an order of magnitude • APC projects use consultants more for front end and commissioning than for whole job • APC software tools are easy enough for the average process and control engineer to use Introduction to Process Control

23. Common Types of Control Strategy • Manual vs. Automatic • Servo vs. Regulator • Open-loop vs. Closed-loop • Control strategies • Feedback Control • Feedforward Control • Cascade Control • Single-Input Single-Output (SISO) vs. Multi-Input Multi-Output (MIMO, also known as multivariable) Introduction to Process Control

24. Temperature indicator Should I adjust the valve or should I run? Emergency cooling Manual vs. Automatic • Manual • Human has to adjust the MV to obtain the desired value of the PV based on observation and prior experiences • Automatic • The computer (or other device) autonomously controls the process and may report status back to a operator Question: Why manual override has to be included in every automatic control systems? Introduction to Process Control

25. 75.5 C… 75.3 C… 75.4 C… o 7.00 AM: 80 C… 8.00 AM: 70 C… 9.00 AM: 60 C… o o o o o Regulator vs. Servo • Regulatory control • Follow constant setpoint, overcoming the disturbance • Servo control • Follow the changing setpoint Question: How to achieve both objectives simultaneously? Introduction to Process Control

26. DV CO PV Process Decisions Controller SP DV CO PV Process Decisions Controller SP Open-loop vs. Closed-loop • Open-loop • Process is controlled based on predetermined scenario Ex.: When food is done in an oven, timers on outdoor lights • Closed-loop • The information from sensor is used to adjust the MV to obtain the desired value of the PV Introduction to Process Control

27. DV SP CO PV Feedback Controller Process Control Strategies (1) • Feedback Control • Corrective action based on process variable (PV) Advantage Requires no knowledge of the source or nature of disturbances, and minimal detailed information about how the process itself works Disadvantage Controller takes some corrective actions after some changes occurs in process variable PV Introduction to Process Control

28. DV CO PV Feedforward Controller Process SP Control Strategies (2) • Feedforward Control • Based on the measurement of disturbance (DV)  feedforward controller can respond even before any changes occurs in PV Advantage Controller takes some corrective actions before the process output is different from the setpoint  theoretically, perfect disturbance rejection is possible! Disadvantage • Requires process model which can predict the effect of disturbance on PV • If there are some modeling error, feedforward control action will be erroneous (no corrective action) • Feedforward controller can be quite complex Introduction to Process Control

29. DV CO PV Feedforward/ Feedback Controller Process SP Control Strategies (3) • Feedback/Feedforward Control • Feedforward controller will adjust CO as soon as the DV is detected • If the feedforward action is not enough due to model error, measurement error and etc., feedback controller will compensate the difference Introduction to Process Control

30. Outer loop Inner loop DV1 DV SP CO PV CO Inner Feedback Controller Inner Process Outer Process Outer Feedback Controller Control Strategies (4) • Cascade Control • The disturbance DV1 arising within the inner loop are corrected by the inner controller before it can affects the PV of the outer one Example: Control valve + positioner Introduction to Process Control

31. Outer loop DV Inner loop DV1 Outer Feedback Controller SP CO PV CO Inner Feedback Controller Inner Process Outer Process Control Strategies (5) • Feedback/Feedforward + Cascade Control Introduction to Process Control

32. DVs … … Process DV COs PVs … Decisions … CO PV … Process Controller Decisions Controller SISO vs. MIMO • Based on how many PV and MV we have in a process SISO MIMO Introduction to Process Control

33. Performances of Process Control System • Closeness to setpoint • Short transient to one setpoint to other setpoint • Smaller overshoot and less oscillation • Smooth and minimum changes of variable manipulation • Minimum usage of raw materials and energy 1 2 2 1, 2 1, 2 1 Regulator Servo 2 Introduction to Process Control

34. The Terms II • Manual control • Automatic control • Open-loop control • Closed-loop control • Feedback control • Feedforward control • Cascade control • Servo control • Regulatory control • SISO control • MIMO control • Transient response • Overshoot • Oscillation Introduction to Process Control

35. Development of a Control System (1) • Open Loop Analysis • What kind of system is considered? • Performance Specifications • How is the system required to behave? • The desired performance must be expressed in terms of the different performance measures that are chosen • Often, depends on the type of control problem to solve • Control Configuration • Which signals are used to calculate the control signal? • Depending on the plant the desired performance specifications and the allowed complexity of the control system • Depending on the type and the number of input signals to the controller different configurations are recognized Introduction to Process Control

36. Development of a Control System (2) • Control Law • Which algorithm is used to calculate the control signal? • Parameter Design (Tuning) • Which are the parameters of the algorithm to calculate the control signal? • Evaluation • How will the controlled system behave in theory?  simulation! • Implementation and Verification • How will the control system be realized? • How does the controlled system behave in practice? • The controller will be implemented and one will verify whether the system is controlled as expected Introduction to Process Control

37. The Terms III • Control law (algorithm) • Parameter design (tuning) • Computer simulation Introduction to Process Control

38. Session Summary • Control has to do with adjusting manipulated variables of the process to maintain controlled variables at desired values • All control loops have a controller, an actuator, a process, and a sensor/transmitter • Various controller strategies can be realized to achieve desired process objectives & product specifications Introduction to Process Control