Using Real Time Automation’s A-B PLC Historian in a Closed OT System

Industrial automation has always walked a fine line between progress and protection. On one hand, modern plants want to capture as much data as possible from their machines to improve efficiency and reduce downtime. On the other hand, exposing sensitive operational systems to external networks introduces real risk. For many organizations—especially those in highly regulated or safety-critical sectors—the safest choice is to keep operations completely sealed off. This approach is known as running a Closed OT system.

A Closed OT system is one where all controllers, historians and devices operate inside a restricted network perimeter. There’s no internet connection, no direct link to corporate IT and no reliance on cloud services. The environment is self-contained, which means the attack surface is dramatically smaller. Utilities, pharmaceutical companies and refineries often favor this model because the stakes of a breach are too high. When the cost of failure is lost power, contaminated product or environmental damage, security and reliability will always win over convenience.

But even within closed systems, the need for accurate operational data doesn’t disappear. Engineers still need to track downtime, quality issues, energy usage and compliance metrics. The challenge is finding a historian that can capture, store and present this data without requiring connections outside the plant. That’s where Real Time Automation’s A-B PLC Historian makes a difference.

The Historian is a hardware appliance designed to run entirely within the OT boundary. It gathers time-stamped data directly from Allen-Bradley PLCs—whether that’s a CompactLogix, ControlLogix, Micro800 or legacy SLC and PLC-5E system—and stores it locally on the device. With storage options of 128 GB, 512 GB or even a terabyte, plants can keep months or years of production data available on-site, without ever sending it into the cloud.

What makes this useful in a closed environment is the flexibility in how the Historian manages information. Operators can schedule data collection to match shifts or production runs. They can configure the system to log only when certain PLC values change. They can even create event-based actions, such as sending a local email alert if a motor overheats or a threshold is crossed. All of this happens inside the perimeter, with no external dependencies.

The Historian also gives teams the ability to transform and model their data before storing it. Instead of working with raw tags, operators can apply logic—adding, subtracting or writing custom functions—so the historian saves only meaningful results. That means less post-processing later and cleaner data for analysis. For visualization, the Historian integrates directly with InfluxDB and Grafana dashboards. Both tools can run on-premises, giving engineers live insight into trends, quality metrics or downtime causes without requiring a single external connection.

In practice, this approach provides tremendous value. A pharmaceutical manufacturer can maintain batch records in compliance with FDA requirements, confident the data never leaves the facility. A water utility can log pump performance and maintenance cycles, while keeping the system air-gapped from outside threats. Food and beverage plants can capture HACCP data in a way that satisfies safety audits without connecting to external servers. Oil and gas operators can store pressure and flow data locally, creating a reliable record even in remote, isolated environments.

Closed OT is not about rejecting digital tools—it’s about controlling them in a way that minimizes risk. With the A-B PLC Historian, plants don’t have to compromise. They can capture and organize valuable production data, visualize it on-site, and export it securely when necessary—all while staying true to the philosophy of isolation.

Of course, not every organization takes this path. While some double down on closed systems, others open their OT environments to IT, creating integration that spans from the shop floor to the enterprise level. That story looks very different, and it’s where IT/OT integration comes in.

Curious how the Historian fits into an open, connected strategy? Check out our companion article: “Bridging IT and OT with Real Time Automation’s A-B PLC Historian.”