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Professor Robert L. Heider, PE

Professor Robert L. Heider, PE. Adjunct Professor, ChE, Washington University ~45 years experience doing “Process Control” Professor for the DPCL, ChE433. Lecture Includes:. What is "process control"? Hardware and Software (firmware)

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Professor Robert L. Heider, PE

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  1. Professor Robert L. Heider, PE Adjunct Professor, ChE, Washington University ~45 years experience doing “Process Control” Professor for the DPCL, ChE433

  2. Lecture Includes: • What is "process control"? Hardware and Software (firmware) • Process measurement instruments; transmitters, transducers, sensor elements, control valves • Flow • Level • Pressure • Temperature • pH • Comments on topics in text

  3. Process Control • Macro vs. micro and nano • Process Control views the process in macro terms • Concerned with interactions of all process variables rather than exact solution of the details of one variable • Can use simulations but does not necessarily require it

  4. Just what is “Process Control?” “Operating a processing plant or facility such that the product quality and production rate specifications are met in a safe and reliable manor.” Involves both hardware and software or firmware functioning together.

  5. Process Control is a general term for the whole plant.Control Loop is the term used to define a single process parameter. • Measurement • Controller • Process Manipulation • Connections or communication between them

  6. Process Control - SPC • Statistical Process Control (SPC) is a technique where the process output or PV is monitored in order to detect an out of control process. • Frequently done with Control Charts • More processes are batch rather than continuous, discrete batches or things properties are controlled through SPC

  7. Process Control - SPC • Shewhart control chart, X-BAR R chart used to detect out of control process • CUSUM and EWMA Charts • SPC does not dictate how much to move or change the process, only that it is out of control • Run-by-Run control is frequently used in semiconductor manufacturing

  8. Measurement • Devices that convert a physical or chemical plant condition to a usable signal.

  9. Process ManipulationMoves or changes the process • Control Valve • Adjustable Speed Drive

  10. Controller • The device or software (firmware) that moves the process to keep the measurement where we want it.

  11. CONTROLLER Temperature TE Element Temp. 101 TC Set 101 Point Temperature TT Transmitter 101 TT TRANSMITTER 101 (line in middle indicates Temperature TC remote control) Controller 101 FY ACTUATOR 101 TE SENSOR Flow 101 FE Element 101 Cooling Manual Water Valve (automatic valve) Pneumatic Valve Electrical Signal (4-20 mA) Pneumatic Signal (3-15 psig) (arrow indicates flow/signal direction) Material Flow Line Process Instrumentation Diagram: Feedback Control – Basic Format Current to pneumatic (I/P) converter AFC Valve failure position chosen for safety and operability Often the sensor is integrated into the transmitter and the I/P converter is integrated into a position controller or “valve positioner” on the actuator that is also not shown on the P&ID.

  12. Process Instrumentation Diagrams:Standard Control Instrumentation Symbols Preceded by area or plant number H L nnn # that uniquely identifies instrument Low Alarm

  13. Lecture Topics • Terminology • Instruments • Temperature • Pressure, level, flow • Control Valves

  14. Transducer – Element; Latin word From Latin trānsdūcere, to transfer : trāns-, trans- + dūcere, to lead A device that converts one type of energy or physical attribute to another for various purposes including measurement or information transfer Also called an “Element” • Transmitter A transducer which responds to a measured variable by means of a sensing element, and converts it to a standardized transmission signal which is a function only of the measured variable.

  15. Discussion Items • Pressure Flow • Level • Control Valves • Temperature Instrumentation

  16. Text Comments, Chapter 9 Output final element linearity – usually is not, consider: SCR Silicon Controlled Rectifier – AC power phase control

  17. SCR phase controlled load results in non-linear output

  18. Instrument Selection • Page 209 of Seborg text • Point 4 MOC, Instruments require better service requirements than pipe or vessel MOC, thin diaphragms, etc • Add point 9, International Codes and Standards as well as special instructions for service requirements • Oxygen cleaning • Nuclear service

  19. Manufacture Support • Most major companies now rely on instrument and control system manufactures for their technical support. • Users groups now substitute for technical societies ABB Siemens

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