PLC-LadderEngineering notes
The PLC-Ladder blog
Ladder and function block diagrams, structured text, simulation, and the maths that bites when control logic meets a real machine. Written by the people building the compiler.
Why Ladder Logic Can't Loop, and the Four Ways Industry Works Around It
Ladder logic has no FOR loop by design. Why, the four workarounds plants use (AOIs, array instructions, one-per-scan, jumps), and our compiler's approach.
Catching Unsafe PLC Logic Before Commissioning: Find Ambiguous Control Behaviour Early
How to catch ambiguous and unsafe PLC control behaviour before commissioning: the six bug classes, simulation-first testing, and structured test injection.
Plain English to PLC Code: How Natural Language Becomes Verified Ladder and FBD Logic
How plain English becomes verified ladder and function block logic: the pipeline from written spec to IEC 61131-3 code, and why verification is the hard part.
Most commissioning rework starts as an unread assumption
Why control logic fails at FAT, and how to surface ambiguity and unsafe behaviour while it is still cheap — before the panel is powered.
PLC Counters Explained: CTU, CTD and Why Edge Detection Matters
PLC counters explained: CTU, CTD and CTUD pin by pin, plus the edge-detection trap that makes one button press count 400 times — and how R_TRIG fixes it.
FBD Programming Examples: 8 Real Circuits Explained Block by Block
Eight FBD programming examples explained block by block: seal-in, timers, flasher, counter, comparator, hysteresis alarm, edge detection and scaling.
PLC Timers Explained: TON, TOF and TP with Ladder and FBD Examples
PLC timers explained: how TON, TOF and TP function blocks work, their IN, PT, Q and ET pins, and real ladder and FBD examples for each timer type.
Structured Text (ST) PLC Programming: Syntax and Examples
Structured Text (ST) for PLCs: variables, IF/CASE, loops, timers and function blocks, with real examples and when to choose ST over ladder.
Ladder Logic for Beginners: Rungs, Contacts, Coils and the Scan Cycle
Ladder logic explained for beginners: rungs, contacts, coils, the PLC scan cycle, series AND, parallel OR, and the seal-in circuit with examples.
Function Block Diagram (FBD) PLC Tutorial, with Examples
Learn Function Block Diagram (FBD) PLC programming step by step: blocks, pins, wires, execution order and when FBD beats ladder logic, with worked examples.
Structured Text to Ladder Logic Converter: How It Works (and How to Verify the Result)
How a structured text to ladder logic converter really works (parse, model, render), why hand translation drifts, and what the diagram can and cannot prove about your intent. Worked example: the three-wire start/stop circuit.
Create Ladder Diagrams Online: A Working Circuit in Your Browser in Two Minutes
Why ladder tooling has been desktop-and-licence-locked, what building a ladder diagram online actually changes, a two-minute walkthrough from an English sentence to a running circuit, and when a desktop IDE is still the right tool.