Lesson Notes By Weeks and Term v4 - SHS 3
AUTOMATION TECHNOLOGIES
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AUTOMATION TECHNOLOGIES
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Subject: Engineering
Class: SHS 3
Term: 2nd Term
Week: 20
Grade code: 3.4.1.LI.2
Strand code: 4
Sub-strand code: 1
Content standard code: 3.4.1.CS.1
Indicator code: 3.4.1.LI.2
Theme: AUTOMATION AND EMBEDDED SYSTEMS
Subtheme: AUTOMATION TECHNOLOGIES
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This lesson introduces the core principles of industrial automation, focusing on the "brain" of modern factories: the Programmable Logic Controller (PLC). We will explore how PLCs read information from the environment using sensors, make decisions based on a program, and control machines like motors and pumps. In Ghana, from the bottling plants in Accra and Kumasi to modern water pumping stations and traffic light systems, automation is key to efficiency, safety, and production. Understanding these technologies opens up exciting career paths in manufacturing, processing, and infrastructure management right here in our country.
2.1 What is an Automation System? An automation system is a setup where machines or processes are controlled automatically, with minimal human intervention. It typically consists of three main parts: Senses (Input Devices): These are the eyes and ears of the system. They gather information about the environment. Brain (Controller): This device processes the information from the inputs and makes decisions based on a pre-written program. The most common controller in industry is the PLC. Muscles (Output Devices): These are the hands and feet of the system. They perform physical actions based on the controller's commands. 2.2 The Components of a PLC System
A. The Brain: The Programmable Logic Controller (PLC) A PLC is a rugged industrial computer designed specifically for controlling manufacturing processes. It replaced thousands of electromechanical relays in old control panels, making systems more reliable, flexible, and easier to troubleshoot. Key Parts of a PLC: CPU (Central Processing Unit): The brain of the PLC; it executes the program. Input Module: Connects the PLC to input devices like switches and sensors. It converts the incoming electrical signals into logic that the CPU can understand. Output Module: Connects the PLC to output devices like motors and lights. It converts the CPU's logic signals into electrical signals to turn devices on or off. Power Supply: Provides the necessary voltage to run the PLC.
B. The Senses: Input Devices (Sensors and Switches) These devices send a signal to the PLC's input module. Pushbuttons: Normally Open (NO): The electrical contact is open by default. Pushing the button closes the contact and allows current to flow. (e.g., a doorbell button). Normally Closed (NC): The electrical contact is closed by default, allowing current to flow. Pushing the button opens the contact and stops the current. (e.g., an emergency stop button). Proximity Sensor: Detects the presence of an object without physical contact. Used on conveyor belts to detect when a product (like a sachet of water or a bottle of FanYogo) is in position. Level Sensor: Detects the level of a liquid in a tank. Essential for automated water pumping systems that fill overhead "polytanks". Limit Switch: A mechanical switch that is activated by the motion of an object. For example, an automated gate uses a limit switch to know when it is fully open or fully closed.
C. The Muscles: Output Devices (Actuators) These devices receive a signal from the PLC's output module and perform an action. Motors: Used to drive pumps, fans, conveyors, etc. Contactors & Relays: An electrically operated switch. A PLC's output is often a low-power signal. This signal is used to energize the coil of a relay or contactor, which can then switch the high-power circuit needed to run a large motor. The PLC tells the relay what to do, and the relay does the heavy lifting. Indicator Lights (Pilot Lights): Used to show the status of a machine (e.g., a green light for "Running", a red light for "Stopped" or "Fault"). Solenoid Valves: Used to control the flow of fluids (liquids or gases). Used in automated irrigation or bottling machines. 2.3 The Language: Introduction to Ladder Logic Ladder Logic is the most common programming language for PLCs. It is designed to look like the electrical relay-logic diagrams that electricians and technicians were already familiar with. Structure of a Ladder Diagram: Rails: Two vertical lines on the sides, representing the positive and negative power supply. Rungs: Horizontal lines where the logic is written. The PLC executes the logic one rung at a time, from top to bottom. Basic Instructions: `--| |--` (Examine If Closed / XIC): Represents a Normally Open (NO) contact. This instruction is TRUE if the corresponding input is ON (e.g., a start button is pressed). It is FALSE if the corresponding input is OFF. `--|/|--` (Examine If Open / XIO): Represents a Normally Closed (NC) contact. This instruction is TRUE if the corresponding input is OFF (e.g., a stop button is NOT pressed). It is FALSE if the corresponding input is ON. `--( )--` (Output Energize / OTE): Represents an output device like a motor or a light. If the logic on the rung is TRUE, the output is turned ON. If the logic on the rung is FALSE, the output is turned OFF. Example: Simple Light Control Task: Turn on a light when a switch is pressed. Components: Switch (Input 0.0), Light (Output 0.0) Ladder Diagram: