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.
How to Test an Ignition HMI Without a PLC: OPC UA Against Simulated Logic
Test an Ignition HMI without a PLC: point the gateway's OPC UA client at simulated logic, bind real tags, and verify screens before the hardware ever arrives.
PLC Online Compiler: Write, Compile and Verify IEC 61131-3 in the Browser
What a PLC online compiler checks and why it matters: types, timer instances, duplicate coils and unreachable logic — compile IEC 61131-3 free in the browser.
Ladder Diagram Maker: Draw and Export Ladder Diagrams Online Free
Draw ladder diagrams online free with a ladder diagram maker that checks your logic: clean diagrams for reports and documentation, plus live simulation.
7 Free PLC Simulators Compared (2026): Browser, Open Source and Vendor Tools
Seven free PLC simulators compared honestly in 2026: PLC-Ladder, PLC Fiddle, OpenPLC, CODESYS, Do-more Designer, CCW and TIA PLCSIM — which fits your need.
How to Test an Ignition HMI Without a PLC: OPC UA Against Simulated
Test an Ignition HMI without a PLC: point the gateway's OPC UA client at simulated logic, bind real tags, and verify screens before the hardware ever arrives.
Connect OPC UA to UaExpert and Ignition SCADA: Step-by-Step Tutorial
How to connect an OPC UA server to UaExpert and Ignition SCADA step by step: endpoints, security policies, certificates, browsing nodes and first live tags.
OPC UA for PLC Programmers: How Your Tags Get From the Controller to Everything Else
OPC UA explained for PLC programmers: what it is, how servers, nodes and subscriptions work, OPC UA vs Modbus vs OPC Classic, and what it means for your tags.
Function Block Diagram Symbols: Every Standard Block and What Its Pins Mean
Every standard FBD symbol explained pin by pin: AND, OR, NOT, TON, TOF, TP, CTU, CTD, R_TRIG, SR/RS, MOVE with EN/ENO and comparators — with ST equivalents.
Structured Text Examples: 10 Real PLC Programs Explained Line by Line
Ten structured text programming examples for PLC: start/stop, timers, counters, CASE state machines, FOR loops, scaling and alarms — explained line by line.
FBD vs Ladder Logic: Which PLC Language for Which Job
FBD vs ladder logic compared honestly: same underlying logic, different readability. Which language fits interlocks, analog, sequences — and when to mix.
Allen-Bradley Ladder Logic: XIC, XIO, OTE and How Rockwell's Rungs Differ from IEC
Allen-Bradley ladder logic explained: XIC, XIO, OTE, OTL/OTU, ONS, TON and CTU in Rockwell terms, mapped to IEC 61131-3 — for Studio 5000 and RSLogix users.
Function Block Diagram Symbols: Every Standard Block and What Its Pins Mean
A reference to FBD symbols in IEC 61131-3: AND, OR, TON, TOF, TP, CTU, CTD, R_TRIG, SR, RS, comparators and math blocks, with every pin explained.