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) Process measurement instruments; transmitters, transducers, sensor elements, control valves Flow Level Pressure Temperature pH Comments on topics in text

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

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. This has a parallel to a personal computer, hardware being the keyboard, monitor. The software performs the calculation that keeps the process at the desired condition or state.

Process Control is a general term for the whole plant 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

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

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

Measurement Devices that convert a physical or chemical plant condition to a usable signal. These are called “instruments” in the control field, they are either in the process pipe line or mounted on a section of pipe or equipment item, tank, etc.

Process Manipulation Moves or changes the process Control Valve Adjustable Speed Drive

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

Process Instrumentation Diagram: Feedback Control – Basic Format TT 101 TC TE FY Cooling Water Manual Valve Temp. Set Point FE Pneumatic Valve Temperature Controller Element Transmitter Flow Pneumatic Signal (3-15 psig) Material Flow Line (line in middle indicates remote control) (automatic valve) Electrical Signal (4-20 mA) (arrow indicates flow/signal direction) CONTROLLER TRANSMITTER SENSOR ACTUATOR 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.

# that uniquely identifies instrument Process Instrumentation Diagrams: Standard Control Instrumentation Symbols Preceded by area or plant number H X Y Z Measurement (optional) Instrument T – Temperature I – Indicator C – Controller P – Pressure R – Recorder T – Transmitter F – Flow E – Sensor V – Valve C - Composition Y – Composition Z – Actuator L – Level A - Alarm H – High W – Weight L – Low D - Density L nnn # that uniquely identifies instrument Low Alarm

Lecture Topics Terminology Instruments Control Valves Temperature Pressure, level, flow Control Valves

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.

Discussion Items Pressure Flow Level Control Valves Temperature Instrumentation

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

SCR phase controlled load results in non-linear output

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

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