Industrial Automation — PLC, SCADA, Modbus and OPC UA
What it is & where it is used
Industrial automation uses control systems — PLCs, DCS, SCADA, robots — to run machines and processes with little human intervention. It is the OT (Operational Technology) side of a factory, as opposed to IT (ERP, email, business apps). Industry 4.0 is largely about connecting the two.
Automation pyramid / Purdue model (ISA-95 levels):
| Level | What lives there | Examples |
|---|---|---|
| 4 — Business | ERP, planning, logistics | SAP, Oracle, Dynamics 365 |
| 3 — Manufacturing operations | MES, quality, scheduling, historian | MES, AVEVA PI, Ignition MES |
| 2 — Supervisory control | SCADA, HMI, engineering stations | WinCC, FactoryTalk View, Ignition, AVEVA InTouch |
| 1 — Control | PLC, DCS controllers, drives, robot controllers | Siemens S7-1500, Allen-Bradley ControlLogix |
| 0 — Field / process | Sensors, actuators, motors, valves | Proximity sensors, RTDs, VFDs, solenoid valves |
Typical industries: automotive, pharma, food & beverage, oil & gas, power, water, semiconductors, packaging.
Versions & history
| Year | Milestone |
|---|---|
| 1968–1969 | First PLC (Modicon 084, Dick Morley) built for General Motors to replace relay panels |
| 1979 | Modbus protocol published by Modicon |
| 1980s | DCS and SCADA spread; Profibus (1989) |
| 1993 | IEC 61131-3 standardises PLC languages (3rd edition 2013) |
| 1996 | OPC (OLE for Process Control, Windows DCOM-based) — OPC DA |
| 1999 | Modbus TCP; Modbus later handed to Modbus Organization (2004) |
| 2003 | PROFINET; EtherNet/IP (2001) |
| 2006–2008 | OPC UA released (platform-independent, secure; IEC 62541) |
| 2009+ | ISA/IEC 62443 series for industrial cybersecurity |
| 2010 | Stuxnet attack on Siemens PLCs — OT security becomes mainstream |
| 2018+ | OPC UA over TSN, OPC UA PubSub/MQTT; companion specifications |
| 2020s | Software-defined/virtual PLCs, IEC 61499 distributed control, IT/OT convergence |
Lifecycle
How a PLC runs (scan cycle), repeated every few milliseconds:
- Read inputs — copy the state of all input modules into the input image table.
- Execute the program — evaluate ladder/ST logic from top to bottom using the image.
- Write outputs — copy the output image to output modules (motors, valves).
- Housekeeping — communications, diagnostics; then repeat. Scan time is typically 1–50 ms.
Automation project lifecycle: requirements & URS → functional design spec (FDS) → I/O list and electrical design → panel build → PLC/HMI programming → FAT (Factory Acceptance Test at the vendor) → installation → SAT (Site Acceptance Test) → commissioning → validation (IQ/OQ/PQ in pharma) → maintenance and change management.
Tools used to develop
- PLC programming: Siemens TIA Portal (S7-1200/1500), Rockwell Studio 5000 (ControlLogix/CompactLogix), CODESYS (many vendors), Mitsubishi GX Works, Schneider EcoStruxure Control Expert, Omron Sysmac Studio, Beckhoff TwinCAT.
- HMI/SCADA: Siemens WinCC (Unified), Rockwell FactoryTalk View, Ignition (Inductive Automation), AVEVA (Wonderware) InTouch/System Platform, GE CIMPLICITY.
- Historians: AVEVA PI System (formerly OSIsoft PI), Ignition historian, InfluxDB, Canary.
- Protocol tools: Modbus Poll/Slave, UaExpert (OPC UA client), Wireshark, Kepware KEPServerEX (driver/OPC server).
- .NET libraries: OPC Foundation UA .NET Standard stack, NModbus / FluentModbus, S7.Net / Sharp7 (Siemens), libplctag (Rockwell), MQTTnet.
- Simulation: PLCSIM (Siemens), Factory I/O, digital twins.