Lecture on Programmable Logic Controllers (PLC)

Jul 1, 2024

Lecture on Programmable Logic Controllers (PLC)

Overview

  • Purpose: Introduction to PLCs, their basics, and some programming examples.
  • Applications: Widely used in industries to control machines.

What is a PLC?

  • Definition: A PLC is a mini computer, often referred to as a "black box".
  • Components:
    • Inputs: Denoted as i1, i2, i3, i4, etc.
    • Outputs: Denoted as q1, q2, q3, q4, etc.
    • Memory: Contains input and output modules.
    • Power Requirement: 24V DC and 0V.
    • Connections: Can be connected to a PC or directly to machine sensors.

Basics of PLC Programming

  • Languages: The main programming languages for PLCs are:
    • Ladder Programming (widely used in industry)
    • Functional Block Diagram

Ladder Programming Basics

  • Symbols:
    • Normally Open Switch (NO): Allows current to flow when pressed.
    • Normally Closed Switch (NC): Current stops when pressed.
    • Output Symbol: Represents outputs like bulbs, pumps, turbines, relays, etc.

Example Programs

AND Logic

  • Condition: Output is on only when all inputs are on.
  • Example:
    • Inputs: IN1, IN2, OUTPUT
    • Logic: Both IN1 and IN2 need to be on for the output to be on.
    • Application: For instance, in a press machine, both buttons must be pressed to start.

OR Logic

  • Condition: Output is on if any one input is on.
  • Example:
    • Inputs: IN1, IN2, OUTPUT
    • Logic: Either IN1 or IN2 being on will turn the output on.
    • Application: Output is on if any one of the conditions is met.

Application in Pneumatic Systems

Pneumatic Circuit Example

  • Components:
    • Double-acting cylinder
    • 5/2 solenoid valve (A+ and A- sides)
    • Magnetic sensors (S1 and S2)
    • Compressor and motor
  • Operation:
    • Air flow is controlled to move the piston back and forth between S1 and S2.

PLC Ladder Logic for Pneumatic Circuit

  • Objective: Automatic to-and-fro motion of the piston.
  • Logic:
    • When at S1: A+ is on, piston moves to S2.
    • When at S2: A+ is off, A- is on, piston moves to S1.
    • Continuous motion is achieved by alternating the states.

Summary

  • PLC: Essential tool in industrial automation.
  • Ladder Programming: Key method for PLC programming.
  • Pneumatic Systems: Practical application of PLCs to control mechanical movements.

Next Steps

  • Upcoming Lectures: More detailed examples and applications.
  • End of Lecture 1