learning industrial controls as an it person

September 26, 2026

Notes on crossing the fence from IT into OT — PLCs, SCADA, MES, and the Purdue model, written down as I learn them.

This started as a plain study outline put together with Claude while figuring out where to even begin. I'm sharing the compiled version because the on-ramp from software into industrial controls is oddly poorly mapped for people coming from where I'm coming from — take the vendor picks as one reasonable path, not the only one, and open an issue if you spot something wrong.

why cross over

Everything I've built professionally lives above an API boundary somewhere. Industrial controls live below one I'd never touched: sensors, relays, motor starters, a PLC scanning inputs in a tight loop, none of it caring what a git blame is. What pulled me in is that the integration problems are the same shape as the ones I already know — moving data correctly and safely between systems that don't trust each other — just wearing different clothes. A PLC talking OPC-UA to a SCADA gateway is not that far, conceptually, from a service talking gRPC to another service. The vocabulary is the barrier, not the concepts.

So this is the guide I wished existed: how the layers fit together, which vendors actually make sense to learn first if you're targeting emerging markets rather than a US/EU plant, and a path that doesn't require owning a factory to get hands-on.

the map: the Purdue model

Before any vendor or protocol, get this hierarchy straight — it's the OSI model of this world, and everything else hangs off it. Low to high:

• Level 0 — the physical process itself: sensors, actuators, motors.
• Level 1 — basic control: PLCs and DCS controllers reading and writing Level 0 I/O.
• Level 2 — supervisory control: local HMIs, area-level SCADA.
• Level 3 — site operations: plant-wide SCADA, MES, historians.
• Level 3.5 (the DMZ) — the IT/OT security boundary. Most of what gets called "systems integration" happens at or across this line.
• Level 4/5 — business systems: ERP, scheduling — the layer most IT people already live in.

Almost all integration work is about moving data safely across these levels, not writing application code the way IT usually means it.

glossary, fast

• PLC (Programmable Logic Controller) — a ruggedized industrial computer that scans inputs, runs logic, and writes outputs in a continuous loop. Programmed per IEC 61131-3: Ladder Diagram, Function Block Diagram, Structured Text, others.
• SCADA (Supervisory Control and Data Acquisition) — the software layer that visualizes and supervises PLCs/DCS across a site: tag database, HMI screens, alarms, trends, historian.
• MES (Manufacturing Execution System) — sits between ERP and the control floor. Tracks work orders, production genealogy, real-time machine status. ISA-95 formally defines this boundary and the data that crosses it.
• OEE (Overall Equipment Effectiveness) — Availability × Performance × Quality. The one KPI manufacturing lives and dies by, usually computed from MES or historian data.
• Systems Integration — connecting the above. Mostly protocol work and data modeling, closer to writing an adapter than building an application.

the stack, and why

I'm building toward emerging markets — Brazil and South America specifically — which changes the calculus from what a US-centric course would recommend. Licensing cost, import lead time, and local support depth matter as much as feature lists.

control layer: siemens, with a shorter word on weg

Siemens (S7-1200/1500, TIA Portal) is the safe default here: the deepest installed base in the region — automotive plants, food and beverage, oil and gas — the largest integrator and technician pool to learn from or eventually hire, local manufacturing presence that softens import duty and lead-time pain, and a used-equipment market deep enough to make hardware cheap once you're past the learning stage.

Worth a shorter passage: WEG, a Brazilian manufacturer with a dominant domestic position in motors and drives, now building out its own CLP line. It matters when a plant already standardizes on WEG motors and drives — one vendor for the whole motor-to-control chain simplifies commissioning — or when local support and zero import friction outweigh Siemens' bigger ecosystem. The trade-off is smaller name recognition outside Brazil if the skill needs to travel.

SCADA: Ignition

Traditional SCADA licensing (Wonderware, WinCC) charges per tag, which gets expensive fast on a real plant and actively punishes learning by trying things. Ignition (Inductive Automation) licenses per server instead — unlimited tags, unlimited clients — and ships a genuinely modern, web-based client (Perspective) alongside the older desktop-style one (Vision). Inductive University, their free training platform, is the best on-ramp I've found for any of this: structured, free, certificate-backed.

the glue: Modbus + OPC-UA

Modbus TCP is the simplest possible protocol here — a client polls a server for coils and registers, no security model, but nearly every PLC and field device speaks it. Good first protocol precisely because there's nothing to hide behind.

OPC-UA is the one that feels like home coming from IT: an object-oriented, structured address space instead of flat registers, with real certificate-based security built in. It's also the primary path from a Siemens S7-1500 into Ignition. (The S7-1200 needs a bit more care — OPC-UA server support depends on the CPU firmware version, check before assuming it's there.)

Where each fits: Modbus for simple field devices and legacy gear, OPC-UA for structured PLC-to-SCADA/MES data exchange.

how i'm actually learning this

1. Electrical fundamentals — digital vs. analog I/O, 4-20mA current loops, relays, motor starters, reading a basic circuit.
2. Siemens ladder logic — TIA Portal plus PLCSIM, its bundled simulator, so no hardware is required to start.
3. Ignition — the Inductive University track, pointed at PLCSIM over a simulated OPC-UA connection.
4. A real integration project — a PLC, real or simulated, talking both Modbus TCP and OPC-UA into Ignition, tags flowing end to end.
5. MES and OEE — the ISA-95 data model, then a simple OEE calculation built on top of simulated machine-state tags inside Ignition.

books and resources

Books

• Industrial Automation: Hands On — Frank Lamb. Written for exactly this IT-to-OT switch, start here.
• Programmable Logic Controllers — Frank Petruzella. The standard PLC textbook.
• Electrical Motor Controls for Integrated Systems — Rockis and Mazur. Electrical fundamentals tied directly to PLC context.
• The ISA-95 standard itself (Enterprise-Control System Integration) — dense, but it's the canonical MES/ERP data model, worth owning rather than reading summaries of.
• SCADA: Supervisory Control and Data Acquisition — Stuart A. Boyer (ISA).

Free or cheap, online

• Inductive University — free Ignition and SCADA training with certificates, the best structured starting point I found.
• RealPars — the best general explainer videos for PLCs, instrumentation, and SCADA, free on YouTube with paid tiers beyond that.
• PLC Fiddle — a browser-based ladder logic simulator, zero hardware required.
• AutomationDirect — free PLC training paired with genuinely cheap hardware.
• r/PLC and r/automation — active, and the IT-to-OT switch is a recurring topic, not a novelty there.

Hardware, cheap first

• Click PLC (~$100, AutomationDirect) — the cheapest real first PLC worth owning.
• A Siemens S7-1200 starter kit — pricier, but matches this stack directly.
• A used Allen-Bradley MicroLogix off eBay — only if a Rockwell-standardized client or job actually needs it.
• Raspberry Pi running Ignition Edge — a cheap, always-on SCADA sandbox.

project ideas, roughly in order

• Simulate a Siemens PLC in PLCSIM, expose it over OPC-UA, connect Ignition to it, build one live HMI screen.
• A Click PLC over Modbus TCP, polled by Ignition — the simplest real-hardware integration available.
• A simulated machine with run/idle/fault states feeding Ignition tags, turned into a basic OEE dashboard: Availability × Performance × Quality, computed for real instead of quoted as a formula.

still missing (running list)

• A step-by-step TIA Portal setup walkthrough.
• An Ignition Gateway install and first-project walkthrough.
• Common ladder logic patterns: start/stop/seal-in, motor interlocks, timers and counters.
• The ISA-95 data model, mapped concretely onto an Ignition or MES data structure.
• IT/OT security basics: the Level 3.5 DMZ, network segmentation, what the actual attack surface looks like.

This page will grow as each of those gets filled in.