PLC Programming Fundamentals: Ladder Logic (LD) vs Function Block Diagram (FBD)

September 08, 2026 - BY Admin

PLC Programming Fundamentals: Ladder Logic (LD) vs Function Block Diagram (FBD)

The Core Languages Powering Modern Industrial Assembly Lines

Programmable Logic Controllers (PLCs) control industrial manufacturing, wastewater treatment, and automotive assembly lines. Programming them requires mastering standard IEC 61131-3 logic languages.

Comparing Industrial Control Logic Paradigms

Different industrial processes call for specific programming styles.

Ladder Logic (LD): Resembles traditional electrical relay ladder diagrams; ideal for digital on/off interlocking.
Function Block Diagram (FBD): Visual blocks with inputs and outputs; preferred for analog signal scaling and PID loops.
Structured Text (ST): High-level text programming ideal for complex mathematics and array sorting.

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