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.
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.

5. 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

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.
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.

9. Process Manipulation Moves 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. Process Instrumentation Diagram: Feedback Control – Basic FormatTT
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.

12. # 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

13. Lecture Topics Terminology Instruments Control Valves 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 ABB Siemens
Most major companies now rely on instrument and control system manufactures for their technical support.
Users groups now substitute for technical societies