Basic PLC Programming — Flashcards

PLC programming involves creating logic, commonly using Ladder Logic (LD), to control industrial machinery via inputs (sensors/buttons) and outputs (motors/lights). Programs follow a scan cycle (read inputs, execute logic, update outputs) structured into rungs, using contacts (conditions) and coils (actions). 

Key PLC Programming Concepts
Ladder Logic (LD): The most common graphical language, resembling electrical relay schematics.
Rungs: Horizontal lines of code containing instructions.
Contacts: Inputs (e.g., normally open, normally closed) representing switch or sensor states.
Coils: Outputs that actuate devices like motors or solenoids.
Logic Functions: AND (series contacts), OR (parallel contacts), and latching (holding an output on).
Timers & Counters: Used to delay actions or count events (e.g., Timer On Delay - TON). 

Basic Workflow
Define I/O: Identify all inputs (sensors) and outputs (actuators).
Select Software: Use vendor-specific software (e.g., Rockwell Studio 5000, Siemens TIA Portal) to create a project.
Develop Ladder Logic: Program the rungs using contacts and coils.
Simulation & Testing: Test logic using simulation tools before deploying to real hardware. 

Common Languages
While Ladder Logic is dominant, IEC 61131-3 standardizes other languages like Functional Block Diagram (FBD), Structured Text (ST), and Sequential Function Chart (SFC).