1. General Introduction to Control
Things we want to control
Plant or Process
Control
Controller
Discrete event control system
Handout 7 control
Topic 3

2. L Plant or Process Plant or process is the target to be controlled.
y(t) is our attention, which is the output of the plant or process.
iv(t) is the input of the plant or process.
L is the set point or goal that the plant’s output or process’s output (y) needs to reach.
A controller is to decide the adjustment on the plant’s input (iv) so that the plant’s output can achieve its goal (L).
Handout 7 control
Topic 3

3. General Introduction to Control
Things we want to control
Plant or Process
Control
Controller
Discrete event control system
Handout 7 control
Topic 3

4. e u Control Decision maker Controller
For the tank plant or process system, u is linked to the valve (IV); so the valve opening or closing is adjusted timely.
e: the plant or process’ output minus the desired output. For the tank, e=y-L.
Handout 7 control
Topic 3

5. plant or process system
Control system or feedback control system
Goal
Plant’s output
Plant’s output
Target system or
plant or process system
actuator
sensor
Controller
Goal/reference/desired/standard
Handout 7 control
Topic 3

6. General Introduction to Control
Things we want to control
Plant or Process
Control
Controller
Discrete event control system
Handout 7 control
Topic 3

7. Discrete event control system
y(t): continuous variable and change with respect to time.
iv(t): continuous variable and change with respect to time.
Y: when y(t)=L, Y=1; when y(t)<L, Y=0.
IV: when iv(t) increases to full opening, IV=1; when iv(t) decreases to full closure, IV=0.
Handout 7 control
Topic 3

8. Discrete event control system
y(t): continuous variable and change with respect to time.
iv(t): continuous variable and change with respect to time.
Y: when y(t)=L, Y=1; when y(t)<L, Y=0.
IV: when iv(t) increases to full opening, IV=1; when iv(t) decreases to full closure, IV=0.
The time that Y=1 or Y=0 occurs is uncertain such that the Y’s dependency on time t is nearly lost. Y=1 or Y=0 becomes an event regardless of time.
The time that IV=1 or IV=0 occurs is also uncertain (as they depend on the event of Y=1 or Y=0) such that the IV’s dependency on time t is nearly lost. IV=1 or IV=0 becomes an event regardless of time.
Handout 7 control
Discrete event control system
Topic 3

9. Discrete event control system
Plant output
Plant input
Controller
Goal or reference
Discrete event control system
Handout 7 control
Topic 3

10. Discrete event control system
Discrete event control system for the tank plant:
Controller:
- input: L and Y; output: IV
- Controller=Decision maker: IF Y=1 THEN IV=0 ELSE IV=1
Control system (including both plant and controller):
- input: L (goal); output: Y (the plant output)
- Given L AND (IF Y=1 THEN IV=0 ELSE IV=1) OR (IF Y=0 THEN IV=1)
Handout 7 control
Topic 3

11. Summary Target to be controlled = Plant or Process.
To any control, there is a goal or reference,
Controller: input: plant’s error; output: plant’s input,
Control system (including both plant and controller): input: goal; output: plant’s output,
Controller is a decision maker and it decides the adjustment on plant’s input in order that plant’s output meets the goal,
Controller is a mapping from plant error to plant input.
Control system is a mapping from goal to plant output.
Handout 7 control
Topic 3