How to Access Data for Optimal Controller Tuning

By Dennis Nash, President & CEO, Control Station, Inc.

Editor’s Note: This article is adapted from the white paper, “Successfully Optimizing Regulatory Controllers Without Risking Data Security.” Download the full paper at https://bit.ly/tj0123cswp to get information about the pitfalls of historical data and some challenges of using live data. Learn how to use “live-historical” data captured via FactoryTalk^® Linx and delivered via the FactoryTalk Live Data interface, and get step-by-step instructions on how to tune PIDs using live-historical data.

The PID controller has been a fixture in manufacturing for decades. From the simple to the complex, the PID remains the primary resource used to regulate industrial production processes. Just as the methods and the tools used to automate production have evolved over the years, so too has the data used in loop tuning and process optimization.

In the past, production and engineering staff performed manual tuning, using analog data to visually estimate the values that would provide the basis for calculations of Gain, Dead-Time, and Time Constant. Manual tuning is still performed today, and although the available data is better, most outcomes are only marginally improved.

Then PID tuning software facilitated a more methodical approach for assessing process data, generating models and calculating parameters. While these early tuning products were limited to uploading and analyzing files, they eventually gained the ability to communicate directly with controllers and access live data.

Today, a challenge for many practitioners is the data itself. In the past, the issue was partially linked to low-resolution historical data, but now, there are growing concerns about cybersecurity and permitting access to a facility’s live data. Fortunately, tuning software now can access high-resolution data that doesn’t put plant security at risk.

Key Points About Live Data

Live data is ideal for modeling and tuning because of its high resolution, but accessing it can present hurdles and create vulnerabilities.

Standard industrial communication protocols such as Open Platform Communications (OPC) allow users to access high-speed, high-resolution data. Live OPC data typically can be accessed using the Rockwell Automation FactoryTalk^® Linx gateway’s OPC server interface. With access to a facility’s raw data, it’s easier to assess a process’ dynamic behavior and calculate an accurate model. Using OPC, process engineers can routinely access data sampled at sub-second speeds.

To tune PID loops using live data, it’s necessary to have data collectors “on” the network. This is more difficult than some might want to acknowledge in part due to the isolated nature of most communications networks and the steady uptick in cyberthreats. A typical production facility may have only a couple workstations connected to the control network. Most IT professionals have an unfavorable view of any third-party software, let alone controller tuning software.

Though PID tuning is a central part of any process optimization initiative, it isn’t essential to day-to-day operations. This view holds true despite the need for high-speed, high-resolution data when tuning. The same applies to monitoring and analytics tools. While all of these belong on a facility’s business network, archived data is substandard for use by most applications.

A High-Resolution Approach

It’s now possible for production and engineering staff to access process data from the business network prior to compression and archiving, addressing the needs for both high-resolution data and network security.