PLC Programming Blog

The difference between movej, movel and movep is the first thing every Universal Robots programmer has to get right. This guide explains joint vs linear vs process moves, when to use each, blend radius, speed and acceleration, and the classic singularity and overshoot pitfalls — with URScript examples.

URScript is the text-based programming language that runs Universal Robots arms. This guide explains what URScript is, how it relates to PolyScope, the core commands (movej, movel, set_digital_out), variables, functions, and how to start learning it without owning a robot.

Modbus TCP vs Modbus RTU compared: both use the same register model and function codes, but RTU runs on serial RS-485 and TCP runs on Ethernet. This post explains the differences, the MBAP header, how to choose, and how to troubleshoot each variant.

Modbus and CAN bus target different environments. Modbus RTU/TCP is the open industrial register protocol for PLCs and process instruments. CAN bus with CANopen profiles connects embedded motion and drive systems. This post explains the architecture, frame format, and when each protocol fits.

Modbus and DNP3 are both fieldbus protocols used to read RTUs and outstations, but DNP3 was purpose-built for utility SCADA — substations, water treatment, and pipelines — with built-in event reporting, data integrity, and time stamping that Modbus lacks. This post explains the differences and when each protocol is the correct choice.

Diagnose DOL motor starter faults across three zones — contactor coil circuit, overload relay, and control circuit. Multimeter sequence, overload trip checklist, and the half-split from PLC output to contactor A1. Links to wiring lab and related posts.

A systematic 7-step PLC fault-finding method covering multimeter discipline, the half-split method, and how to navigate every fault family — from wiring opens to scan-order bugs. Links to live fault scenarios and wiring fault labs.

PROFINET and EtherCAT both run on Ethernet hardware, but they solve different problems. PROFINET integrates Siemens PLCs with drives and I/O in a standard plant network. EtherCAT delivers microsecond cycle times for high-axis-count servo and CNC applications. This post explains how each works and when to choose one over the other.

SCADA and BMS both supervise equipment and collect data — but they target different environments, use different protocols, and serve different operators. This post explains what each system does, where they overlap, and when a building needs both.

SCADA monitors and controls real-time plant operations. MES manages production orders, schedules, quality, and traceability. They operate at different time horizons and different abstraction levels — but they must talk to each other.

Incremental encoders output a pulse train — you count pulses to track relative position, but lose it on power loss. Absolute encoders output a unique digital word for every shaft position — position is retained across power cycles. Learn when to use each, how to wire them, and how PLCs read both types.

Inductive sensors detect metal only. Capacitive sensors detect anything — metal, plastic, liquid, or powder. Learn how each works, how to wire NPN vs PNP output, and how to pick the right sensor for your application.

Modbus vs PROFIBUS compared: register model vs device profile, RS-485 vs RS-485 DP, speed, diagnostics, vendor support, and when each protocol still makes sense in 2026.

Modbus is a communication protocol. RS-485 is an electrical standard for wiring. They are not the same thing — Modbus RTU runs on RS-485, but so does PROFIBUS. Here is the difference, why it matters, and how to wire it correctly.

A motor starter is a contactor plus an overload relay. This post explains what the overload adds, when you need a full starter vs a bare contactor, how the PLC interlocks with both, and wiring to the control circuit.

Motor starter vs VFD compared: DOL starting vs variable speed, energy savings, starting current, soft start, mechanical wear, and when the extra cost of a VFD is justified.

NPN sensors sink current (pull signal to 0V when active). PNP sensors source current (pull signal to +24V when active). The mismatch between sensor output and PLC input type is the most common discrete wiring mistake. This explains how to read your sensor datasheet, identify your PLC input type, and wire them correctly.

Practical PLC encoder programming examples for Delta, Siemens S7-1200, Allen-Bradley CompactLogix, and Mitsubishi FX. Covers high-speed counter setup, quadrature mode, homing, and position-based output control in each dialect.

PROFINET vs EtherNet/IP: Siemens vs Rockwell, IRT real-time classes vs CIP motion, conformance levels, cable topology, and where Modbus TCP fits when you need something simpler.

SCADA vs DCS compared: integrated platform vs open supervision layer, continuous process vs discrete manufacturing, response time, vendor lock-in, and the convergence happening right now.

SCADA vs HMI: an HMI is a panel for one machine; SCADA is a server supervising dozens of PLCs. This post covers architecture, historian, alarms, scope, and which one a controls engineer actually needs.

SCADA vs PLC explained clearly: what each layer does, who runs the logic, who runs the display, why a PLC keeps running when SCADA goes offline, and which one you need to learn first.

Thermocouples cover wide temperature ranges with simple wiring. RTDs (PT100) are more accurate and stable. Thermistors are accurate over a narrow range at low cost. Learn the trade-offs, wiring, and PLC module requirements for each.

Four fully worked analog input PLC programming examples: 4-20mA to PSI scaling (including the 4mA offset trap), tank level %, temperature with deadband, and valve % output. The maths shown, wiring noted, Allen-Bradley and Siemens dialect explained.

24V control power, control vs power circuits, relays, contactors, motor starters, terminal blocks, wire numbers — and the five wiring mistakes beginners make. Practical guide for panel wiring.

Learn what FactoryTalk View ME, SE and Studio are, why the download hunt is frustrating, which concepts transfer to any HMI, and how to build those skills free in your browser.

A vendor-neutral HMI programming tutorial covering screens, tag binding, pushbuttons, lamps, numeric entry, alarm design, and ISA-101 colour discipline. Practical and concept-first.

Learn how to read a P&ID (piping and instrumentation diagram) from scratch. Covers ISA-5.1 symbols, the tag-letter decoder, two worked examples, and how to build an I/O list from a drawing.

PLC vs HMI explained clearly: what each does, who runs the logic, how they communicate, common beginner confusions, and a side-by-side comparison table.

Relays and contactors both use a coil to switch contacts. The difference is scale, rating, and application. This guide explains construction, current ratings, motor starters, and when each belongs in a control panel.

WinCC Classic, WinCC Unified, WinCC OA, and WinCC TIA-integrated — which one should you care about? This honest guide untangles the Siemens HMI family and shows how to learn the transferable skills free.

Free, browser-based PLC simulators compared — no install, no license. Ladder and structured text tools for beginners, ranked honestly with a comparison table.

Ladder logic suits discrete interlocks and relay replacement; function block diagram suits analog, PID, and reusable logic. Compare LD vs FBD and pick the right one.

Eight classic PLC programming examples with full ladder logic solutions and explanations — motor seal-in, timers, counters, traffic lights, tank control and star-delta.

How PLC programming differs from Python, C and Arduino: the scan cycle, ladder vs relay logic, determinism, and whether a software dev can make the switch.

RSLogix 500 programs SLC 500 and MicroLogix; Studio 5000 programs ControlLogix and CompactLogix. Compare hardware, addressing, and which to learn in 2026.

Siemens and Allen-Bradley are both industry-standard PLC platforms. Compare software, hardware, cost and job market to decide which one to learn first.

An honest overview of Allen-Bradley and Rockwell certification in 2026: the Rockwell training routes, where ISA's CCST fits in, what it all costs, and a self-study plan to get certified faster on Studio 5000 and RSLogix.

A complete bottle filling PLC program walkthrough — the index, stop, fill, cap and release sequence, the I/O, fill-valve ladder logic, a fill-cycle timing diagram, and timed vs flow-meter filling explained.

Conveyor belt PLC programming explained with worked ladder logic examples — start/stop seal-in, photo-eye part counting and diverting, jam handling, plus the I/O layout, timing diagrams and a state machine for a real conveyor.

How to program an elevator with a PLC. The I/O wiring, the lift state machine, call-button seal-in rungs, door timers, nearest-floor dispatch logic and the safety interlocks every elevator PLC program needs.

A fair roundup of free PLC programming software in 2026 — vendor free tiers (CCW, TIA Portal, GX Works), OpenPLC, CODESYS and the zero-install browser simulator. What's actually free, what the catch is, and which to pick for your goal.

An HVAC PLC program example for an air handling unit. AHU PLC programming with ladder logic, temperature deadband control, fan proving, economizer dampers, and heating vs cooling mode logic.

Is PLC programming a good career? Yes — strong demand, solid pay and a clear path from technician to senior. Here is who it suits, the pros and cons, how it compares to robotics and SCADA, and how to get started.

What Jump To Subroutine (JSR) does in a PLC, how JSR/SBR/RET work together, calling subroutines with parameters, and the Allen-Bradley, Siemens and IEC 61131-3 equivalents — with ladder diagrams.

What the master control relay (MCR) instruction does in a PLC, how an MCR zone de-energises a section of rungs, the difference between MCR and JMP/AFI, and why an MCR is never a substitute for a hardwired E-stop.

One shot ladder logic explained. How rising-edge and falling-edge detection works, R_TRIG and F_TRIG, the Allen-Bradley ONS/OSR one-shot, P/N edge contacts, timing diagrams and the pitfalls that bite beginners.

A practical guide to open-source PLC software. What OpenPLC, Beremiz and matiec actually are, how the open-source PLC stack fits together, IEC 61131-3 language support, when free open-source PLC programming software is the right choice — and when it isn't.

PLC counters explained in plain English. How the CTU up-counter, CTD down-counter and CTUD up/down counter work, the CU/CD/RESET/PV/CV/Q parameters, ladder logic examples, and the IEC 61131-3, Allen-Bradley, Siemens and Mitsubishi names.

A categorised hub of worked PLC programming examples and ladder logic examples — motor control, sequencing, process and sensing — each with an explanation and a link you can open in a free browser simulator.

Pump control logic in a PLC explained with ladder diagrams. Start/stop on level, seal-in rungs, duty standby alternation, lead lag pump control and automatic fault changeover — with state, timing and architecture diagrams.

A complete PLC programming roadmap that shows exactly what skills to learn and in what order — from electrical basics and ladder logic through timers, seal-in logic, analog and PID, HMI and comms, to real projects.

A PLC state machine, Grafcet and Sequential Function Chart (SFC) explained in plain English. How to break a sequence into steps and transitions, implement it in ladder with Set/Reset coils or CASE in Structured Text, and stop writing spaghetti logic.

How PLC temperature control works, from the RTD or thermocouple input to the heater output. A worked temperature control using PLC ladder diagram, on/off vs PID, hysteresis, and a control-logic flowchart.

How to get a Siemens PLC certification in 2026 — the SCE self-learning, SITRAIN and third-party online routes, the exact TIA Portal skills they assess, a 10-week study plan, and how it compares to a Rockwell certification.

A practical structured text programming tutorial. IF, CASE, FOR, WHILE and timers in ST with copy-paste examples, the IEC 61131-3 data types, and how to practise in a browser PLC simulator.

The variable table and cross-reference are the two most powerful debugging tools in a PLC IDE. Learn how to use them to find faults faster, understand program structure, and verify logic before commissioning.

Comparing structured PLC curriculum learning against self-directed study with manuals, YouTube, and practice time. Which approach gets you to job-ready faster, and how to combine both.

A comprehensive comparison of 8 PLC programming dialects — syntax differences, addressing schemes, market penetration, and which to learn for your target industry. With the same example program in all 8 dialects.

The PLC simulator sandbox lets you write any ladder logic program against a live machine model without completing a structured scenario. Learn how to use it for experimentation, portfolio projects, and dialect practice.

Fault injection inserts hidden wiring faults, logic errors, or sensor failures into a running PLC simulation. Learn how it works, what types of faults it covers, and why it is more effective than reading about fault-finding.

A practical guide to using scan-cycle highlight in PLC programming — what it shows you, how to enable slow mode, and how to use it to diagnose timer bugs, rung order problems, and latch coil issues.

OpenPLC vs CODESYS compared honestly: licensing and cost, supported hardware and runtimes, operating systems, IEC 61131-3 language support, learning curve, and who each tool actually suits. Plus: is OpenPLC free, and OpenPLC alternatives.

The 20 most common PLC programming interview questions with detailed example answers — covering scan cycle, ladder logic, timers, faults, and vendor-specific topics. For junior to intermediate candidates.

PLC timers explained in plain English. How TON, TOF and TP timers work, the IN/PT/Q/ET parameters, timing diagrams, ladder logic examples, and the IEC 61131-3, Allen-Bradley and Siemens names.

Step-by-step traffic light PLC program. Design the Red→Green→Yellow→Red sequence with timers, build the I/O list, draw the state and timing diagrams, and wire the ladder logic — then run it in a free browser simulator.

A practical 30-day study plan for the ISA Certified Control Systems Technician (CCST) exam — what topics it covers, recommended resources, and how to use a PLC simulator to practise the programming sections.

Comparing IEC 61131-3 Instruction List (IL) and Siemens Statement List (STL/AWL) — syntax, use cases, compatibility, and whether either is still worth learning in 2026.

How inductive proximity sensors detect metal targets using electromagnetic fields, how to wire PNP and NPN types to a PLC input, and how to use them in ladder logic programs.

The five most common PLC programming mistakes beginners make: wrong contact type, scan-cycle order bugs, latch coil misuse, timer preset errors, and ignoring edge detection. With examples.

Comparing Mitsubishi GX Works and Allen-Bradley Studio 5000 ladder logic syntax, addressing schemes, and programming conventions. Which dialect should you learn first?

A practitioner's guide to PLC programming certifications — Rockwell CCP, Siemens ST-PRO, TÜV FSE, ISA CAP, Ignition Core, plus the portfolio-based alternatives that hiring managers increasingly prefer. Which paths have ROI, which are tax, and how to combine them.

A curated list of genuinely free PLC training — YouTube channels, vendor free tiers, open-source tools, and our own free scenarios. Covers what's worth learning for zero budget, which free certificates have real signal, and when paying finally makes sense.

LogixPro shipped in 2002 and changed how PLC programming was taught. Twenty-four years later, modern browser-first simulators have overtaken it on nearly every axis. Here's an honest comparison — when LogixPro still makes sense, and when a newer tool does more for less.

Codesys is the most widely embedded PLC runtime in the world. Our simulator is a browser-based curriculum with graded scenarios. This post explains exactly when each tool wins — and why most learners benefit from using both in sequence.

OpenPLC is a genuinely excellent open-source PLC runtime. It's also not a complete learning platform on its own. This post compares OpenPLC against paid simulators — what each does well, where they complement each other, and which one is right for your situation.

A detailed, tested ranking of PLC simulators in 2026 — our own, OpenPLC, Codesys, PLC Fiddle, LogixPro, vendor demos, and the rest. Covers real IEC 61131-3 compliance, graded assessments, dialect coverage, and whether each tool actually teaches you to program a PLC.

An introduction to safety PLCs for standard-PLC engineers — what makes a controller 'safety-rated,' what SIL levels actually mean, and where the boundary is between a safety function and normal control. Covers GuardLogix, S7-1500F, Omron NX-Safety, and why you can't just code your way to SIL 2.

A practical guide to analog I/O (4–20 mA, 0–10 V) and PID tuning for PLC programmers. Covers scaling, the three PID terms in plain English, and a step-by-step tuning method that works on 90% of loops without Ziegler-Nichols wizardry.

A practical Delta PLC training guide — DVP micro-PLCs, AS-series mid-range, AH high-end, all programmed in ISPSoft. Covers IEC 61131-3 support, CANopen and Modbus, and a 6-week self-study path that uses cheap hardware to get you productive.

A practical Mitsubishi PLC training guide covering FX3U/FX5U micro, Q-Series mid-range, and iQ-R modern controllers in GX Works3. Addressing conventions, free software, used-hardware sourcing, and how to build portable IEC-compliant skills even on a Japanese-market vendor.

A practical Omron PLC training path from entry-level CP1L micro-PLCs to modern NJ and NX controllers in Sysmac Studio. Where to get hardware cheaply, which software is free for learners, and how to build portable skills even if your employer runs a different brand.

If you searched 'PLC training near me,' there are three realistic options: a local community college course, a vendor-run classroom, and a laptop-plus-USD-99-a-year online path. This post walks the trade-offs, five decision questions, and a hybrid stack that beats both for most budgets.

SCADA — Supervisory Control And Data Acquisition — is the software layer above PLCs that handles visualisation, historians, alarms, and reporting. This post explains what SCADA does, where it ends and the PLC begins, and why learning both together is the right move.

A complete TIA Portal tutorial for newcomers — install, configure an S7-1200, write a start/stop rung in LAD, add a small SCL function block, and run everything in PLCSIM. No hardware required, 21-day trial is enough.

A step-by-step RSLogix 5000 (now Studio 5000 Logix Designer) tutorial for complete beginners. Create a project, add I/O, build a tag database, write a start/stop rung with XIC/XIO/OTE, wrap it in an Add-On Instruction, and download to an emulator. No prior Rockwell experience required.

A practical guide for learners who want to practice industrial control panel wiring and physical-fault diagnosis without a hardware bench. What you can learn online, what you can't, and how to structure deliberate practice.

Side-by-side TON, R_TRIG, and TOF idioms across 8 PLC dialects — IEC, Allen-Bradley, Siemens, Mitsubishi, Schneider, Delta, Omron, IL.

A gentle, non-jargon guide to PLC programming for people with no electrical background. Covers the scan cycle, your first rung, the five things that will confuse you, and a four-week starter plan that you can follow in a browser without installing anything.

The Coding Tutor is live — 96 hands-on lessons across 8 PLC dialects, all browser-based and free. Same physical scenario, eight different ways to write the logic.

A buyer's guide to online PLC training — video courses, subscription academies, graded simulators, and free alternatives. Which formats build real skill, which signal well on a CV, and which are paid YouTube. Includes recommended paths for students, career switchers, and working engineers.

A practical guide to Siemens PLC training — S7-1200, S7-1500, TIA Portal, SCL structured text, PROFINET, and S7-1500F safety. What the ST-PRO1 classroom gets you, where self-study beats it, and a 10-week plan that produces a Siemens-fluent engineer for under USD 250.

Basic PLC programming is a surprisingly small set of patterns — maybe twenty rungs — that appear in almost every real program. Learn them in the right order, in the browser, with automated tests, and you will never have to re-learn the fundamentals.

A practical, self-study Allen-Bradley training path — RSLogix Micro to Studio 5000, Logix family, FactoryTalk View, EtherNet/IP — that takes 10–12 weeks, costs USD 99–249, and produces a portfolio a hiring manager can verify in 10 minutes.

What does a PLC programmer earn in the US in 2026? Honest salary ranges by experience level, role, industry, and region — for technicians, controls engineers, and systems integrators.

PLC and SCADA are two different disciplines that have to be learned together to be useful in a modern plant. This guide explains where the boundary is, why most trainees fail at SCADA, and how to build both skills in 16 weeks using a browser-first simulator plus Ignition or Wonderware free tiers.

A practitioner's guide to PLC certifications in 2026 — vendor certificates (Rockwell, Siemens), IEC 61131-3 proficiency, safety/SIL, and the portfolio-based alternatives that hiring managers increasingly prefer. What's worth paying for, what's a tax, and how to build a stack that actually signals competence.

An online PLC simulator is a browser-based environment where you write ladder logic or structured text, wire it to simulated I/O, and run it against machine physics without any install. Here's what to look for, who it's for, and what a good one feels like in 2026.

A 12-week PLC programming course that takes you from zero electrical background to writing production-grade ladder logic for Allen-Bradley, Siemens, and IEC PLCs. Self-paced, browser-based, no install, no vendor lock-in.

Compare the best PLC simulators for students in 2026: browser-based, desktop, free, and paid options. Includes OpenPLC, Codesys, LogixPro, and browser simulators.

A practical self-teaching roadmap for becoming a PLC programmer: from absolute beginner to job-ready. Covers free resources, simulator practice, certification options, and portfolio building.

PLC vs microcontroller (MCU) compared in depth: ruggedisation, I/O, programming, real-time scan, environment, cost at scale and lifespan. Learn the difference between a PLC and a microcontroller, why use a PLC instead of an MCU, and how to choose.

Learn how PID controllers work in PLCs: proportional, integral, and derivative terms explained. Includes practical tuning methods and IEC 61131-3 code examples.

TON, TOF, and TP are the three standard IEC 61131-3 timer function blocks. Learn how each works, when to use each, and how they map to Allen-Bradley and Siemens syntax.

The 25 most common PLC programming interview questions with detailed answers. Covers scan cycle, ladder logic, timers, counters, PID, safety, and troubleshooting.

IEC 61131-3, Allen-Bradley RSLogix/Studio 5000, and Siemens TIA Portal each use different syntax and naming conventions. Compare addressing, data types, timers, and more.

Learn to read ladder logic diagrams: rails, rungs, contacts, coils, timer and counter blocks. Step-by-step guide with real examples for complete beginners.

Ladder logic is graphical and widely supported; structured text is textual and powerful for maths. Compare syntax, use cases, and job market demand to choose your first PLC language.

A seal-in rung keeps a coil latched after the momentary start signal drops. Learn how to build reliable seal-in circuits with stop, overload, and E-stop protection.

The PLC scan cycle is the continuous read-execute-write loop at the heart of every controller. Learn what happens in each phase and why scan time matters for your control programs.

A PLC (Programmable Logic Controller) is an industrial computer that reads sensor inputs, runs a control program, and switches outputs on or off. Learn how it works in plain English.