Hi everybody! I’m Jim Cahill, author of the Emerson Process Experts blog and am delighted to be able to guest post here on the Analytic Expert site. The objective of my blog is to be your connector with the experts around Emerson Process Management, including the Rosemount Analytical team. I’ve featured their expertise over the years in the Analyzer category.
Instead of pretending to be an expert, I’ll highlight the work of Greg McMillan and pH control. If you’re not familiar with Greg, he was named as a Process Automation Hall of Fame member by ControlGlobal.com in 2001. He authors the Control Talk blog and is a frequent contributor on the ISA Interchange blog.
He is also the author of numerous process automation-related books including Advanced pH Measurement and Control, 3rd Edition. He also founded the ISA mentor program to pass along his wisdom to the next generation of process control and instrumentation professionals.
Here’s a presentation Greg gave on pH Control Solutions from two years ago.
The presentation includes 3 major sections: pH opportunity and challenge (slide 7), modeling and control options (slide 24), and plant design and maintenance (slide 71). Each section concludes with key points to summarize concepts and practical guidance for you.
For example, in the pH opportunity and challenge section, one of Greg’s key points is:
Slope of the titration curve at the set point has the greatest effect on the tightness of pH control as seen in control valve resolution requirement. The next most important effect is the distance between the influent pH and the set point that determines the control valve rangeability requirement.
An example from the modeling and controls section is:
Filter the feedforward signal to remove noise and make sure the corrective action does not arrive too soon and cause inverse response.