SCADA (Supervisory Control and Data Acquisition) is the software and server layer that sits above the PLCs and RTUs. It collects data from the controllers, shows it to operators, raises alarms, records history and sends commands or setpoints down. Control logic and interlocks stay in the PLC or RTU in the field. NIST SP 800-82r3 (section 2.3.2) describes classic SCADA as a system for dispersed assets such as pipelines, water distribution and power grids, where centralized data acquisition matters as much as control. In Vietnamese plants, "SCADA" usually means the central supervisory software connected to many PLCs, and that is how this article uses the term.
How SCADA differs from PLC, HMI, DCS, historian and MES
| Component | What it does | Where it runs | Examples |
|---|---|---|---|
| PLC / RTU | Reads sensors, runs logic, PID and interlocks, drives valves and motors | Control panels in the field; RTUs at remote sites | ControlLogix, CompactLogix |
| HMI | Screen where operators see process status and history and change setpoints (NIST SP 800-82r3, p. 11) | Panel at the machine or an operator station | PanelView Plus, OptixPanel |
| SCADA | Gathers data from many PLCs/RTUs; central alarms, trends, reports, supervisory control | Servers and clients in the control room | FactoryTalk View SE, AVEVA System Platform, Ignition |
| DCS | Controls production at one location: a supervisory level coordinates several local controllers that share one process (NIST, section 2.3.3) | Refineries, chemical plants, power and water treatment | PlantPAx (Rockwell) |
| Historian | Stores tag values over time for trends, analysis and reports | Server in the control room or on a higher-level network | FactoryTalk Historian, AVEVA Historian |
| MES | Manages production operations: orders, traceability, performance | Plant-level network | — |
The ISA-95 page on isa.org places PLCs and DCSs at Level 2, lists MES together with SCADA at Level 3 and ERP at Level 4. Many other diagrams draw HMI/SCADA at Level 2. The point to remember is that SCADA sits between the controllers and production management.
The line between SCADA and DCS keeps blurring, because both have servers, operator stations and historians. A DCS such as PlantPAx comes with process controllers that have a default tasking model and a library of process instructions (PROCES-SG001X, p. 37). SCADA is usually separate software that connects to PLCs from many vendors.
A typical plant SCADA architecture
Field devices → PLC/RTU → control network → SCADA servers → operator clients and historian → MES/ERP
- Field devices: sensors, valves, drives, power meters, and packaged equipment with their own PLCs.
- PLC/RTU: runs logic and interlocks. In SCADA for dispersed assets, RTUs or PLCs at remote sites control local actuators, and intelligent electronic devices (IEDs) such as protective relays may connect straight to the server (NIST, section 2.3.2).
- Network: EtherNet/IP, Modbus TCP or Modbus RTU inside the plant; fiber, radio or leased lines to remote sites. For high-availability systems, see DLR vs PRP. If you put firewalls between zones, see which ports a FactoryTalk system needs.
- SCADA servers: data server (drivers to the PLCs), alarm server, display server. NIST notes that a control center typically has the control server, HMIs, engineering workstations and the historian on one LAN.
- Clients: operator stations, engineering stations, and web or thin clients for offices.
- Historian: stores time-series data and feeds reports and higher-level systems.
Choosing a SCADA platform: what you have to decide
| Question | Why it matters |
|---|---|
| How many tags and clients, and how is licensing counted? | Vendors count differently: by tags or displays, per server, per module, or as a subscription. This sets the cost of every future expansion. |
| Do you need redundancy, and for which parts? | Data servers, display servers, alarms and historian can each be redundant; network and power need planning too. |
| Web clients or installed clients? | Web clients need no installation and suit offices and phones; access rights and security need planning. |
| What protocols do your existing PLCs speak? | Native drivers for what you have (EtherNet/IP for Allen-Bradley, Modbus, Siemens S7…) or a path through OPC. |
| Historian included or separate? | Number of logged tags, retention period, how reports get the data out. |
| Which standards for alarms and screens? | ISA-18.2 for alarm management, ISA-101 for HMI design. |
| Who will maintain it? | Which platform the plant team already knows; what documentation and training exist. |
Three protocols you will meet:
- OPC UA: the OPC Foundation describes it as a platform-independent, service-oriented architecture that brings the older OPC Classic specifications together, with encryption, authentication and an information model that gives data its context. A good fit when connecting several vendors or passing data to higher-level systems.
- EtherNet/IP: per ODVA, the Common Industrial Protocol (CIP) running over standard Ethernet and TCP/IP. It is the main network for ControlLogix and CompactLogix.
- Modbus: per the Modbus Organization, an application-layer protocol that runs over serial lines (RS-232, RS-485, in RTU or ASCII framing) and over Ethernet via TCP/IP. Common on power meters, drives and packaged equipment.
Alarms and screens: ANSI/ISA-18.2-2016 sets out requirements and recommended practices for managing alarm systems in the process industries; ISA-101.01-2015 gives guidance on designing, implementing, operating and maintaining HMIs. How to apply both on a new or upgraded SCADA: SCADA upgrades: redo HMI and alarms to ISA-101 and ISA-18.2.
Platforms TDL integrates
The information below comes from each vendor's public pages and documents (read 25 Oct 2026). It is grouped by vendor and is not a ranking. Pricing and license terms change over time; TDL confirms them with the vendor when quoting.
| Platform | Vendor's description | Clients | Redundancy, per vendor documents | Licensing, per vendor page |
|---|---|---|---|---|
| FactoryTalk View SE (Rockwell) | HMI/SCADA from a single workstation up to a distributed system | Installed clients; web/mobile via FactoryTalk ViewPoint; thin clients via ThinManager | Redundant HMI server pair; FactoryTalk Linx data server redundancy (VIEWSE-UM006S) | Station and Server licenses; subscription ordering available |
| FactoryTalk Optix (Rockwell) | HMI, data visualization, IIoT and edge platform; web-based design (FactoryTalk Hub) | Panels, stations, web clients; Windows and Linux | Version 1.8: three-node high-availability runtime cluster (release notes) | Runtime entitlement subscriptions, "pay only for what you use" |
| AVEVA System Platform | Object-based SCADA platform with reusable templates; add application engines to scale out | OMI runs on devices and in web browsers | Not described on the product page — see AVEVA documentation | Not detailed on the product page; AVEVA offers the Flex subscription program |
| AVEVA InTouch HMI | HMI software with a situational-awareness graphics library and integrated AVEVA Historian | HTML5 web client, no installation | Not described on the product page | InTouch Unlimited: perpetual license; Premier edition through Flex |
| Ignition (Inductive Automation) | Web-based SCADA software, clients launched from a central server | Zero-install web-launched clients, mobile | Master/Backup gateway pair | Per server, unlimited clients, tags and connections |
| N3uron | Industrial edge platform for IIoT and DataOps, built from nodes and modules | Web Vision: browser-based HMI/SCADA | Redundancy Agent: primary/backup connection pairs to data sources | Per node and module, unlimited clients, screens and tags |
FactoryTalk View SE has three application types: local station (one computer), network station and network distributed (VIEWSE-UM006S, Oct 2025, version 16). It is the natural route for plants already on ControlLogix and FactoryTalk.
FactoryTalk Optix runs on Windows, Linux, OptixPanel and Embedded Edge Compute. Rockwell lists complete OPC UA support, native drivers for other vendors' PLCs (Siemens S7, Codesys, TwinCAT) alongside Logix tags and alarms, and MQTT connectivity.
AVEVA System Platform models equipment as objects built from templates; change a template and the derived objects follow. It runs on premises, in the cloud or hybrid, includes a process historian and exchanges data over MQTT.
Ignition is licensed per server. Its OPC UA module includes drivers for Allen-Bradley Ethernet, Modbus Ethernet, Siemens Ethernet, DNP3, Omron, BACnet, IEC 61850 and Mitsubishi; the historian writes to an SQL database.
N3uron runs on Windows, Linux and ARM devices. Its acquisition modules include OPC UA Client, Modbus Client, EtherNet/IP Client (ControlLogix, CompactLogix, PLC-5, SLC 500, MicroLogix, Micro800) and MQTT; the Historian module stores data in EmbeddedDB, TimescaleDB or MongoDB.
Related services: SCADA and historian, Ignition integration, AVEVA integration. If you are replacing an old HMI/SCADA, see Legacy HMI/SCADA migration paths.
Frequently asked questions
Can SCADA replace the PLC?
No. SCADA collects data from the controllers, shows it to operators, raises alarms, records history and sends commands or setpoints down; control logic, PID and interlocks stay in the PLC or RTU in the field.
What is the difference between HMI and SCADA?
An HMI is a screen where operators see process status and history and change setpoints, at the machine or at an operator station (NIST SP 800-82r3, p. 11). SCADA gathers data from many PLCs/RTUs onto servers and clients in the control room, with central alarms, trends, reports and supervisory control.
Our plant has PLCs from several vendors. Can one SCADA cover them all?
Yes: SCADA is usually separate software that connects to PLCs from many vendors. Check whether the platform has native drivers for the PLCs you have (EtherNet/IP for Allen-Bradley, Modbus, Siemens S7…) or needs a path through OPC; OPC UA is a good fit when connecting several vendors. Adding equipment to an existing SCADA: Small SCADA fixes and extensions.
What is the difference between SCADA and DCS?
NIST SP 800-82r3 describes classic SCADA as a system for dispersed assets such as pipelines, water distribution and power grids (section 2.3.2), while a DCS controls production at one location, with a supervisory level coordinating several local controllers that share one process (section 2.3.3). A DCS such as PlantPAx comes with process controllers that have a default tasking model and a library of process instructions (PROCES-SG001X, p. 37), while SCADA is usually separate software that connects to PLCs from many vendors. The line between the two keeps blurring, because both have servers, operator stations and historians.
Sources
- Rockwell Automation, PROCES-SG001X-EN-P, PlantPAx Distributed Control System Selection Guide, System Release 5.50, 08/2026 — p. 37
- Rockwell Automation, VIEWSE-UM006S-EN-E, FactoryTalk View Site Edition User's Guide v16.00.00, 10/2025
- OPC Foundation, Unified Architecture
- ODVA, EtherNet/IP
- Modbus Organization, Introduction to Modbus
- Rockwell Automation, FactoryTalk View Site Edition (product page)
- Rockwell Automation, FactoryTalk Optix (product page)
- Rockwell Automation, FactoryTalk Optix release notes (1.8.x): "System features"
- AVEVA, AVEVA System Platform (product page)
- AVEVA, AVEVA InTouch HMI (product page)
- Inductive Automation, Unlimited Licensing
- Inductive Automation, SCADA Software
- Inductive Automation, Ignition OPC UA Module
- Inductive Automation, Ignition 8.1 User Manual: Ignition Redundancy
- N3uron, N3uron (home page)
- N3uron Academy, What is N3uron
- N3uron Docs, EtherNet/IP Client
- N3uron Docs, Historian
- N3uron Docs, Web Vision
- N3uron Docs, Redundancy Agent
- NIST, SP 800-82r3, Guide to Operational Technology (OT) Security, 09/2023 — p. 11 and sections 2.3.2, 2.3.3
- ISA, ISA-95 Standard: Enterprise-Control System Integration
- ISA, ANSI/ISA-18.2-2016, Management of Alarm Systems for the Process Industries
- ISA, ISA-101 Series of Standards
Read 25 October 2026. This article paraphrases the sources and does not quote them; read the original documents before designing or working on a system. Links open the latest edition in Rockwell's literature library; page numbers refer to the edition cited.