How Siemens, Emerson, IDEC and Weidmuller modernize SCADA

On many plant floors, serial Modbus devices still run next to EtherNet/IP PLCs, which run next to newer sensors that speak OPC UA and MQTT. Christopher Deloglos, strategic product manager for Weidmuller's u-OS, says that mix of technology generations is what holds back digital projects. He made the point in an Automation World Q&A published Nov. 5, in which contributing writer Mat Dirjish asked product specialists at Siemens, Emerson, IDEC and Weidmuller the same set of SCADA modernization questions.

Their answers agree more than the four logos would suggest. None of the four told manufacturers to rip out working controllers. Each described a translation layer between old equipment and new systems instead. For a controls engineering manager or a utility operations director planning a retrofit, that moves the hard decisions to three places: where data gets normalized, how much of it stays local, and which interfaces carry it to the business systems above.

Four ways to build the bridge

Linda Htay, automation product marketing manager at IDEC, explained the basic approach. Plants keep their older machines and add edge devices, HMIs, gateways or controllers that can talk to both the legacy equipment and modern platforms. Those devices collect the data, put it into a standard form and send it on securely over MQTT, OPC UA, Modbus TCP or EtherNet/IP. IDEC builds the bridge into the operator panel. It offers its FT1J/FT2J and HG1J/HG2J HMIs as a link between existing controls and cloud analytics, and its FT2J combined PLC and HMI as a communication layer for retrofit projects.

Siemens uses the SCADA software itself. Alan Cone, a WinCC product specialist, described two kinds of gateway: hardware that plugs into devices and converts data types before output, and software on a separate machine that translates one format into another. To reach the cloud, WinCC includes a service called WinCC Cloud Connector, which uses OPC UA and MQTT.

Weidmuller puts the work on an edge operating system. In Deloglos's design, one device handles several protocols, aggregates the data and republishes it in a standard, meaningful format. Emerson works one level higher. Adam Schindewolf, product marketing manager for Emerson's Aspen Technology business, described Inmation as a data fabric between OT systems and IT or cloud users. It pulls in live data from control systems and historians, adds context, and publishes it through MQTT, REST APIs or direct cloud connectors. Filtering and aggregation happen on-site as the data arrives, so only relevant data travels to the cloud.

Read together, the four answers suggest that the bridge is the most important spec in a legacy retrofit, and that its location changes who maintains it. A bridge built into the HMI belongs to the controls team. A data fabric above the historians sits closer to IT. For plants where a corporate analytics group is the main customer for the data, that location could decide which budget pays for the project.

Fast data and long retention

Deloglos described the storage problem plainly. A high ingest rate and long retention pull in opposite directions, so the answer is tiers. On u-OS, through the PROCON-Connect app or third-party databases running in containers, high-frequency data is captured near the source. That avoids the latency and bandwidth cost of sending every point to a central server. Full-resolution data stays local for a set period. Then downsampled, aggregated or change-based data moves to a central historian or the cloud.

Siemens handles the same problem with acquisition rules. Cone said WinCC Historian can collect data cyclically, on change, on events or with hysteresis, and offers separate fast and slow tag logging to limit disk writes without losing data. Emerson filters at ingestion. The three approaches differ, but they lead to the same planning task: someone has to decide which signals keep full resolution, for how long, and what gets thrown away. That is a retention policy, and it belongs in the design documents before the first gateway ships.

That split is a fair test of the edge-layer thesis. Tiered storage solves bandwidth. It does not settle who owns the archive at the top tier. A plant can standardize its gateways and still be choosing between a proprietary historian and an open database ten years from now.

Connector licenses for ERP and MES

The link to business systems is where the four answers differed most. Cone said WinCC provides MQTT and OPC UA connectors for ERP and MES, plus GraphQL and REST APIs, and lets users write their own communication drivers. Deloglos listed three built-in Data Hub APIs on u-OS: REST over HTTP with JSON for simple access, NATS for high-performance messaging, and a real-time interface for the lowest latency. Integrators can also run Node-RED on the device to format payloads and route them to a specific ERP or MES endpoint without writing a custom application.

Deloglos also drew a commercial contrast. He set open, documented APIs against fixed lists of proprietary ERP connectors that each carry a license fee. That makes it a procurement question as much as an engineering one, because the connector model decides what each new link to the business systems will cost.

Fort Smith chose to consolidate

Not every operator needs a bridge. The Utility Department of Fort Smith, Arkansas, which provides water and wastewater service to 150,000 people, replaced its SCADA instead. A case study from Inductive Automation, last updated in October 2025, describes how the city replaced five Wonderware SCADA systems with one Ignition platform, working with Little Rock system integrator Brown Engineers. The old systems had gone in at different times and ran different software versions. HMIs weren't uniform, naming conventions differed, and data was stuck at each facility.

Utility director Lance McAvoy said the old systems used to keep him up at night. Now he can watch the plants, the distribution system and the collection system from one terminal and diagnose problems remotely across four treatment plants, two of them in other counties. Operators moved between plants used to find that red, green and yellow meant different things at each site. Now every plant uses the same screens.

Fort Smith paid two-thirds of the upgrade price to replace five SCADA systems with one, and got a utility where red means the same thing at every plant.

The architecture details matter as much as the price. Brown Engineers set up five gateways with master/backup redundancy, routed through the city's central IT facility and linked over Ignition's Gateway Area Network, which syncs data across sites. The integrator also built a conversion tool that imported text-format data from the legacy systems, standardized it and created tags for the new platform. That is the same normalization the four vendors describe doing at the edge. Fort Smith did it once, during migration.

This looks like a counterpoint to the bridge approach, but it fits the same pattern. Fort Smith's five systems came from one vendor and did similar work, which made full consolidation practical. A plant running three generations of protocols from several suppliers is in a different spot. In that case an edge layer could be the realistic first step, and consolidation could come later if it happens at all.

Systems that outlast their projects

An October piece in Control Engineering, drawing on systems integrator Actemium Avanceon, explains why these choices outlast the project that makes them. A controls project has a finish date. The system it creates can stay in production for 10, 15 or 20 years. When each project is scoped separately, standards drift, sites solve the same problems in different ways, and the manufacturer ends up coordinating among its own integrators. The piece's sharpest point is about scale. A choice that's cheap on one project can be expensive when repeated across 20 sites, while a reusable naming standard or shared data model can pay back well beyond its first job.

Market researchers report the same shift on the services side. Fortune Business Insights, in a report updated Oct. 26, projects the global industrial automation services market at $202.20 billion in 2026. It says service providers are moving from one-off system integration toward long-term partnerships that cover continuous optimization and enterprise data strategy. ABB's Stefan Basenach, head of process automation technology, described a similar split in an ABB-sponsored Automation World podcast. In his view, embedded controllers still have a place in process automation, while operator-level software is moving away from Windows server farms toward more decoupled architectures. Weidmuller's containerized edge fits that second direction.

So the gateway spec and the tag-naming standard belong in the same document for any plant now scoping a SCADA retrofit. The open question is who owns that standard after commissioning, when the integrator has left and the next project team arrives. Fort Smith's answer was one platform. Most mixed-vendor plants will have to answer it with a written policy.