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Process Control

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Process Control

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Process Control

  1. 1. Process Control Architectures EEE465 1999 Lecture 3 Includes material from lectures by Rick Kazman and Mary Shaw and by Prof. Dr. Florian Matthes Major Greg Phillips Royal Military College of Canada Electrical and Computer Engineering [email_address] +01-613-541-6000 ext. 6190
  2. 2. Data Flow Systems <ul><li>A data flow system is one in which </li></ul><ul><ul><li>the availability of data controls the computation </li></ul></ul><ul><ul><li>the structure of the design is dominated by orderly motion of data from process to process </li></ul></ul><ul><ul><li>the pattern of data flow is explicit </li></ul></ul><ul><li>In a pure data flow system, there is no other interaction between processes </li></ul><ul><li>Classes of data flow systems: </li></ul><ul><ul><li>batch sequential </li></ul></ul><ul><ul><li>pipe and filter </li></ul></ul><ul><ul><li>process control </li></ul></ul>
  3. 3. Warning: Process control is specialized field, requiring significant study and experience. Control system development for physical systems should be undertaken only by trained experts. Don’t try this at home.
  4. 4. Open Loop Temperature Control Return air Heated air Furnace
  5. 5. Closed Loop Temperature Control Return air Heated air Furnace Thermostat Gas valve control Temperature sensor Temperature setting control
  6. 6. Process Control Terms <ul><li>Process variables </li></ul><ul><li>Controlled variable </li></ul><ul><li>Input variable </li></ul><ul><li>Manipulated variable </li></ul><ul><li>Set point </li></ul><ul><li>Open loop system </li></ul><ul><li>Closed loop system </li></ul><ul><li>Feedback control </li></ul><ul><li>Feedforward control </li></ul>
  7. 7. Feedback Control Process Controlled variable Controller  ’ s to manipulated variables Set Point Input variables
  8. 8. Feedforward Control Process Controlled variable Controller  ’ s to manipulated variables Set Point Input variables
  9. 9. Process Control Paradigm <ul><li>Computational elements </li></ul><ul><ul><li>process definition </li></ul></ul><ul><ul><li>control algorithm </li></ul></ul><ul><li>Data elements </li></ul><ul><ul><li>process variables </li></ul></ul><ul><ul><li>set point </li></ul></ul><ul><ul><li>sensors </li></ul></ul><ul><li>Control loop relation </li></ul>
  10. 10. Process Control Style Process Controlled variable Controller Manipulated variables Set Point Computation Data Flow
  11. 11. Choosing a Control Architecture <ul><li>Consider a closed-loop control design when </li></ul><ul><ul><li>the task involves continuing action, behaviour, or state </li></ul></ul><ul><ul><li>the software is embedded in a physical system </li></ul></ul><ul><ul><li>uncontrolled (open loop) computation does not suffice, usually because of external perturbations or imprecise knowledge of external state </li></ul></ul>
  12. 12. Example: Cruise Control System Cruise control system system on/off engine on/off pulses from wheel accelerator brake increase/decrease speed resume speed clock throttle Problem block diagram
  13. 13. Cruise Control System: Booch’s Object-oriented Architecture Clock Current speed Desired speed Throttle Accelerator Engine Brake Driver Wheel
  14. 14. Cruise Control System: Garlan’s Decomposition <ul><li>Computational elements: </li></ul><ul><ul><li>process (the engine) </li></ul></ul><ul><ul><li>control algorithm (maintains current speed) </li></ul></ul><ul><li>Data elements </li></ul><ul><ul><li>controlled variable: current speed of vehicle </li></ul></ul><ul><ul><li>manipulated variable: throttle setting </li></ul></ul><ul><ul><li>set point: desired speed and active/inactive setting </li></ul></ul><ul><ul><li>sensor for controlled variable: wheel pulses, which is converted to speed using a clock </li></ul></ul>
  15. 15. Cruise Control System: Garlan’s Process Control Architecture Engine Wheel rotation Controller Desired speed Active/inactive toggle Pulses from wheel Throttle setting The set point consists of the desired speed and the active/inactive toggle . Desired speed can only be calculated when the system is active, and is based on the system on and increase/decrease speed inputs. Active/inactive status is calculated based on the engine on , system on , accelerator , brake , current speed , and resume inputs.
  16. 16. Cruise Control System: Garlan’s System Architecture Control unit State machine for toggle Event table for desired speed desired speed active/inactive toggle Clock wheel rotation
  17. 17. Next Class: Data Flow Implementation

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