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Programmable Logic Controllers (PLCs) - Coggle Diagram
Programmable Logic Controllers (PLCs)
Overview
Definition
Industrial-grade computer
Replaces relay logic circuits
Performs control functions
Advantages
Increased reliability
Flexibility in programming
Lower cost than relay-based systems
Faster response time
Applications
Manufacturing processes
Real-time system control
Use in high-speed environments
Parts of a PLC
Central Processing Unit (CPU)
"Brain" of the PLC
Executes logic and controls communication
Includes microprocessor, memory, and diagnostics
Input/Output (I/O) Modules
Interfaces with field devices
Fixed or modular configurations
Optical isolation for electrical separation
Power Supply
Supplies DC power to PLC modules
Larger systems require external power supplies
Programming Device
Used to write and enter programs
Handheld devices or PCs
Supports ladder logic programming
Principles of Operation
Input Monitoring
Reads field device status
Converts signals into memory states (logic 1 or 0)
Program Execution
Executes ladder logic program sequentially
Updates outputs based on logic
Output Control
Operates in real-time
Outputs updated after each program scan
Modifying the Operation
Relay-Based Changes
Requires physical rewiring
PLC-Based Changes
Program updates without rewiring
PLCs vs. Computers
Hardware Differences
PLCs are rugged and designed for industrial use
Computers include peripherals like keyboards
Operating Environment
PLCs handle high temperatures and electrical noise
Computers suited for controlled environments
Programming
PLCs use ladder logic or simple programming languages
Computers support higher-level programming languages
PLC Size and Application
Classification by Size
Nano: Less than 15 I/O points
Micro: 15-128 I/O points
Medium: 128-512 I/O points
Large: Over 512 I/O points
Application Types
Single-ended One PLC controlling one process
Multitask: One PLC controlling multiple processes
Control Management: One PLC supervising several others
Memory Considerations
Memory size depends on the application
K values (e.g., 1K = 1024 words)