Lecture 1

Discrete-state Process Control

Learning Outcome

• Identify a discrete-state process control system and characterize it.

• Design a simple relay-based discrete-state control system and document it using the proper circuit diagram.

• Appreciate Programmable Logic Controllers as universal discrete-state process controllers in industrial applications

Textbook reading

• Page 387 – 396

• Page 403 – 405

• Section 8.4

• Section 8.5.2

• Section 8.5.3

Process Control

Controller

Set Point

Feedback

Output

What is Discrete-State Control?

• not continuous control

• on / off control

• can be sequential control

More advances

• timer / counter

Discrete Control

• The controller only provide ON / OFF control

• Discrete Input – ON / OFF state such as push button, switch, floating switch, proximity switch, optical switch, etc.

• Controller – Switch, Relay, Contactor

What is the different between Relay and contactor?

• Relay– operates as the heart of the relay ladder control– operates at low voltage and low current, e.g. 12V and 2

4V d.c.– 1P1T to 4P8T

• Contactor– operates at power voltage, e.g. 220V / 380V– Contacts carry the load current such as motor current– With auxiliary contacts for the relay ladder (low voltage

and low current)– Main contacts – 2P1T to 4P1T

• What is a relay controller?

• What is an electronic controller?

• What is a PLC?

Activity

• Design a Star-Delta Starter for a 3-phase 380V 10kW induction motor

• Draw the power circuit and control circuit separately