Lesson Notes By Weeks and Term v5 - Grade 9

Lesson Video

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Performance objectives

• Explain the operation of a simple pneumatic system.
• Understand how a transistor works as a switch in a circuit.
• Describe the basic principles of a Programmable Logic Controller (PLC).
• Differentiate between open-loop and closed-loop systems.
• Identify common sensors in control systems.

Lesson summary

This week, we delve deeper into systems and control, focusing on more advanced mechanical and electrical systems. This is important because these systems are all around us, powering our lives and driving technological advancement. From the automated gates at shopping malls to the sophisticated irrigation systems used in agriculture, understanding how these systems work equips you with the knowledge to potentially design, build, maintain, and improve them. In a country like South Africa, where innovation and skills development are crucial for economic growth, grasping these concepts is invaluable.

Lesson notes

2. 1. Pneumatic Systems Pneumatic systems utilize compressed air to perform work. They are commonly used in applications requiring high force and speed, such as in manufacturing plants and automated machinery.

Components of a Pneumatic System: Compressor: Compresses air and stores it in a reservoir. It's the source of power for the system.

Reservoir (Air Tank): Stores the compressed air. It ensures a consistent supply of air for the system.

Air Lines (Hoses): Transport the compressed air to different components.

Control Valves: Control the flow of compressed air. These valves direct the air to different parts of the system, determining the direction and speed of actuators.

Actuators (Cylinders): Convert the compressed air energy into mechanical motion, usually linear (pushing and pulling).

Regulator: Controls the air pressure, ensuring it doesn't exceed safe or optimal levels.

Lubricator: Adds a fine mist of oil to the air to lubricate moving parts and prevent wear.

Working Principle: The compressor compresses air, which is stored in the reservoir. When a control valve is opened, compressed air flows through the air lines to the actuator. The pressure of the air causes the piston inside the cylinder to move, producing linear motion.

Example: Automatic Doors Consider automatic doors at a shopping mall. A motion sensor detects someone approaching. This signal activates a solenoid valve (an electrically controlled valve) which directs compressed air to a pneumatic cylinder. The cylinder extends, pushing the door open. When the person passes, the motion sensor no longer detects movement, the valve closes, and the cylinder retracts, closing the door. 2.

2. Transistors as Switches A transistor is a semiconductor device used to amplify or switch electronic signals and electrical power. In this context, we'll focus on using a transistor as a switch.

NPN Transistor: Base (B): Controls the flow of current between the collector and emitter.

Collector (C): The positive terminal connected to a power source through a load (e.g., LED, buzzer).

Emitter (E): Connected to ground (0V).

Working Principle: A small current applied to the base (B) allows a larger current to flow between the collector (C) and the emitter (E). If no current is applied to the base, no current flows between the collector and emitter. Thus, a small current at the base switches the flow of current in the main circuit.

Example: LED Control Imagine an LED connected in series with a resistor (to limit current) between the collector and the positive terminal of a battery. The emitter is connected to ground. A push button switch is connected between the base and a resistor connected to the positive terminal of the battery. When the push button is not pressed, no current flows to the base, and the LED remains off. When the button is pressed, a small current flows to the base, causing the transistor to conduct. This allows current to flow through the LED, lighting it up.

Circuit Diagram: ``` +V (Battery) --- Resistor --- Collector (C) of Transistor --- LED --- Resistor (Current Limiting) --- Ground (GND) +V (Battery) --- Resistor --- Push Button --- Base (B) of Transistor Emitter (E) of Transistor --- Ground (GND) ``` 2.

3. Programmable Logic Controllers (PLCs) A PLC is a specialized computer used to control automated processes. They are widely used in industrial automation, robotics, and process control.

Components of a PLC: CPU (Central Processing Unit): The "brain" of the PLC, executing the control program.

Input Modules: Receive signals from sensors and switches (e.g., temperature sensors, pressure sensors, limit switches).

Output Modules: Send signals to actuators (e.g., motors, valves, solenoids).

Programming Device: Used to create and download the control program to the PLC (usually a computer).

Power Supply: Provides power to the PL

C. Working Principle: The PLC continuously scans its inputs, executes the control program (logic ladder diagram or other programming language), and updates its outputs. The control program defines the relationship between the inputs and outputs.

Example: Traffic Light Control A PLC can be used to control traffic lights at an intersection. Input devices would include loop detectors in the road that sense the presence of vehicles. The PLC program would be designed to switch the traffic lights based on the presence of vehicles on each road and pre-set timing sequences. Output devices would include the lights themselves. 2.

4. Open-Loop vs. Closed-Loop Control Systems Open-Loop Control System: The output of the system does not affect the control action. The system operates without feedback.

Example: A toaster. You set the timer, and the toaster operates for that amount of time, regardless of whether the bread is actually toasted to your liking.

Advantages: Simple, inexpensive, and easy to design.

Disadvantages: Less accurate and susceptible to disturbances.