Control Global

Control Talk Blog

The Control Talk Blog provides guidance from a user's viewpoint on the design of automation systems, equipment, and piping for process control improvement. Details are offered on the selection and installation of PID controllers, control valves, variable speed drives, and measurements to maximize loop performance. The blogs are often more intensive and extensive and less vendor specific than a white paper. The goal is an advancement of the profession by sharing conceptual principle based knowledge.

Greg McMillan is a retired Senior Fellow from Solutia/Monsanto and an ISA Fellow. At present, he contracts with Emerson DeltaV R&D via CDI Process & Industrial in Austin and consults for MYNAH Simulation Technologies in Saint Louis. Greg received the ISA Kermit Fischer Environmental Award for pH control in 1991, received the Control magazine Engineer of the Year Award for the Process Industry in 1994, was inducted into the Control magazine Process Automation Hall of Fame in 2001, was honored by InTech magazine in 2003 as one of the most influential innovators in automation, and received the ISA Life Achievement Award in 2010.

Also, you can read McMillan's monthly Control Talk Column printed in Control magazine.

Insights to Process and Loop Performance

Submitted by Greg McMillan on Fri, 07/07/2017 - 18:25
Here we look at a myriad of metrics on process and control loop performance and show how to see through the complexity and diversity to recognize the commonality and underlying principles. We will see how dozens of metrics simplify to two classes each for the process and the loop.

Fixes for Deadly Deadband

Submitted by Greg McMillan on Sun, 06/04/2017 - 15:51
While there are some cases where deadband is helpful, in most applications the effect is extremely detrimental and confusing. Deadband can arise from any sources either intentionally or inadvertently. Deadband creates deadtime and for certain conditions excessive and persistent oscillations.

When and How to use Pulse Width Modulation of Controller Outputs

Submitted by Greg McMillan on Wed, 04/05/2017 - 14:32
In some applications, throttling of the manipulated flows is difficult or impossible. In the biochemical industry, where precise (good resolution and sensitivity) throttling valves without any crevices (to meet sanitary requirements) are rather limited (there are exceptions such as the Fisher Baumann 83000-89000 series).

Getting the Most Out of Valve Positioners

Submitted by Greg McMillan on Wed, 03/01/2017 - 18:04
Today’s smart digital valve positioners have incredible capability and flexibility as to tuning, performance and diagnostics. Here we look at how to get the most out of these positioners by tuning and by making sure the valve assembly does not hinder performance and gives the position feedback needed.

Uncommon Knowledge for Achieving Best Feedforward and Ratio Control

Submitted by Greg McMillan on Tue, 01/31/2017 - 15:53
Here are key relatively straightforward principles and practices not commonly known that can make a world of difference in the performance of feedforward and ratio control systems. Also, guidance is offered for the setup and automatic identification of the parameters needed by the use of software designed to tune PID...

PID Options and Solutions - Parts 2 and 3

Submitted by Greg McMillan on Tue, 11/01/2016 - 19:46
Here we finish up the extensive presentation of how to get the most out of your PID. We start with a look at the contribution of each mode and show how to estimate performance metrics from tuning settings and how excessive integral action and insufficient proportional action create oscillations.

PID Options and Solutions - Part 1

Submitted by Greg McMillan on Wed, 09/28/2016 - 19:04
The major types of process responses and the different worlds of process applications are presented. Additionally, the oversight of not including and understanding the contribution of automation dynamics is addressed. The discussion of the response of the PID is started.