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Examoogle • User • info@examoogle.com • EE-2024-8821
Chapter 1 of 12 • Page 1 of 248🔒 Protected PDF • Watermarked
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Operation of PLC control by?
CPU
Data RAM
User Prog. RAM
System RAM
CPU
Quick Summary: The Central Processing Unit (CPU) is the brain of a Programmable Logic Controller (PLC). It executes the user-programmed logic, monitors input status, and updates output modules based on the program execution results.
The Central Processing Unit (CPU) is the brain of a Programmable Logic Controller (PLC). It executes the user-programmed logic, monitors input status, and updates output modules based on the program execution results.
Tscan=Tinput+Tlogic+Toutput — Represents the total cycle time of the PLC CPU.
The CPU follows a repetitive cycle known as the scan cycle: (1) Input Scan: reads physical signals from input devices; (2) Program Execution: solves the logic ladder program stored in memory; (3) Output Scan: updates the physical output states to control external equipment.
The CPU maintains a cyclical scan process essential for real-time control.
Memory includes System RAM (for OS), User RAM (for ladder logic), and Data RAM (for I/O status).
CPU performance dictates the response time of the automated system.
High reliability in harsh industrial environments.
Modular architecture allowing flexible system expansion.
Requires specialized programming knowledge.
Higher initial cost compared to simple relay logic controllers.
Factory automation and assembly lines.
Process control systems in oil and gas refineries.
System RAM is used by the operating system for housekeeping tasks.
Data RAM (or Image Table) stores the current status of physical inputs and outputs.
User Program RAM stores the ladder diagram or functional block code created by the engineer.
A is correct — The CPU is the core processor that executes the user logic and manages the operational scan cycle of the PLC.
In competitive exams, remember that while memory stores the program, the CPU is the engine that interprets and executes that program.