Why is a book on pH measurement important to automation professionals?
pH measurement and control is critical for food, beverage, pharmaceutical, and many chemical products, as well as water quality and waste treatment. It represents an important variable for many processes, yet it is often the most difficult to control. A proper understanding prepares automation professionals to grapple with precipitous responses and difficult diagnostics and build an intuition for solving problems that might otherwise seem intractable.
Since the first edition was released, what technological advance has made the biggest impact in measuring pH?
Manufacturers have made significant advances in the life, accuracy, and response time of glass electrodes—especially for higher temperatures—and in the stability and equilibration time of reference electrodes. There have also been advances in the precision of control valves, dynamic simulations, digital twin functionality, and PID control algorithm capability, most notably external-reset feedback.
What is a digital twin, and what role does it play in system design?
The digital twin provides an exact replica of the control system and operator interface. This replica is joined with a dynamic simulation of the process and equipment, including the often-overlooked dynamic response of measurements and control valves. The digital twin uses a universal method to rapidly compute pH for complex solutions via an expanded charge balance that provides enough fidelity for real-time control simulation. Experimenting with the digital twin allows engineers to find and verify the most cost-effective, best-performing, and reliable process, mechanical, piping, and automation system design.
What are different types of titration curves, and why don’t the curves match?
Laboratory titration curves are plots of lab pH versus the ratio of reagent to sample volume. Field titration curves are plots of field pH measurement versus the ratio of reagent to feed flow. These curves often do not match because of the difference between field and lab electrodes and changes in sample pH due to changes in temperature, dissolution, and evaporation. Computer-generated titration curves have these same problems with a significant additional problem of ignoring the dramatic curve slope moderation, particularly in strong acids, due to the carbon dioxide absorption from the simple exposure of the process fluid to air.
What challenges may technicians face when working on control valves and pH measurement, and how does your book help address those challenges?
The documentation provided by suppliers for control valves, flowmeters, electrodes, and transmitters typically does not address the design and installation needed for pH control.
This book focuses on factors that are truly important in achieving the five Rs (rangeability, repeatability, resolution, reliability, response time) and the key features needed when selecting and using instrumentation.
What are the top key takeaways for your readers?
pH systems offer composition measurement and control that is unequaled in terms of precision and rangeability but pose exceptional challenges. These challenges include addressing extraordinary sensitivity and nonlinearities and consequential equipment, piping, electrode, control valve, and control strategy and tuning requirements. This book provides insight into the importance of these factors and simple and effective ways to understand and handle these challenges.
Who is this book best suited for?
Everyone responsible for a successful pH application needs this book, including anyone selling, designing, installing, or maintaining pH systems.About the Authors
About Gregory K. McMillan
McMillan is the author of numerous ISA books and columns on process control, and he has been the monthly Control Talk columnist for Control magazine since 2002. He started and guided the ISA Standards and Practices committee on ISA-TR5.9-2023, PID Algorithms and Performance Technical Report, and he wrote “Annex A - Valve Response and Control Loop Performance, Sources, Consequences, Fixes, and Specifications” in ISA-TR75.25.02-2000 (R2023), Control Valve Response Measurement from Step Inputs.
McMillan’s achievements include the ISA Kermit Fischer Environmental Award for pH control in 1991, appointment to ISA Fellow in 1991, the Control magazine Engineer of the Year Award for the Process Industry in 1994, induction into the Control magazine Process Automation Hall of Fame in 2001, selection as one of InTech magazine’s 50 Most Influential Innovators in 2003, the ISA Life Achievement Award in 2010, and the ISA Mentoring Excellence award in 2020.
He has a BS in engineering physics from Kansas University and an MS in control theory from Missouri University of Science and Technology, both with emphasis on industrial processes.
About Christopher Stuart
About Dean Cook
About Zachary Sample
