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

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 GOALS Practical Industrial Process Control: Understanding, Tuning & Autotuning Control Loops Introduction to Process Control

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 Controller Process Sensor + Transmitter + Actuator Practical Industrial Process Control: Understanding, Tuning & Autotuning Control Loops Introduction to Process Control

Time Table Day Time Day 1 Day 2 Day 3 Day 4 Day 5 08.00-09.30 Opening, Introduction to Industrial Process Control PID Control I Tuning Methods of PID Controller + Lab. III Cascade Control I Feedback/ Feedforward Control + Lab 10.00-11.30 Actuators PID Control II Autotuning Methods of PID Controller + Lab. Cascade Control II + Lab. Feedback/ Feedforward + Cascade Control + Lab 12.30-14.00 Sensor/Transmitter, Filtering Tuning Methods of PID Controller + Lab. I Practical Troubleshooting I Feedforward Control I Demo 14.30-16.00 Process Dynamic Modelling Tuning Methods of PID Controller + Lab. II Practical Troubleshooting II Feedforward Control II + Lab. Final Test, Closing Practical Industrial Process Control: Understanding, Tuning & Autotuning Control Loops Introduction to Process Control

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

Session Outlines & Objectives 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

Definition (1) Process Control 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 Process Raw Materials Products Energies Out Introduction to Process Control

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 Corrective Action Knowledge Data Process Information Introduction to Process Control

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 Brain: Control calculation Eyes: Sensor Steering wheel: Actuator Introduction to Process Control

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 Feed Condensate Product Stream Steam TT TC Introduction to Process Control

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 Fluid LT LC Introduction to Process Control

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

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

Goal of Process Operation Safety & Reliability Product Specification Environmental Regulation Operating Constraint Efficiency Maximum profit 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!!! Introduction to Process Control

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

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 Old Controller New Controller Introduction to Process Control

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

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

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

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

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 New Controller Improved Performance Introduction to Process Control

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 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

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

Manual vs. Automatic Manual Automatic 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 Emergency cooling Temperature indicator Should I adjust the valve or should I run? Question: Why manual override has to be included in every automatic control systems? Introduction to Process Control

Regulator vs. Servo Servo control Regulatory control Follow constant setpoint, overcoming the disturbance Servo control Follow the changing setpoint 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 Question: How to achieve both objectives simultaneously? Introduction to Process Control

Open-loop vs. Closed-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 DV PV CO Process Decisions Controller SP DV PV CO Decisions Controller Process SP Introduction to Process Control

Control Strategies (1) Feedback Control Feedback Process Controller 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 DV SP PV Feedback Controller CO Process Introduction to Process Control

Control Strategies (2) Feedforward Control Feedforward Process 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 DV SP PV CO Feedforward Controller Process Introduction to Process Control

Control Strategies (3) Feedback/Feedforward Control Process 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 DV SP PV CO Feedforward/ Feedback Controller Process Introduction to Process Control

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 DV SP PV CO Outer Feedback Controller Inner Feedback Inner Process Outer DV1 Inner loop Outer loop Introduction to Process Control

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

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

Performances of Process Control System 1 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 2 2 1, 2 1, 2 1 Regulator Servo 2 Introduction to Process Control

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

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

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

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

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