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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