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.

Secondary Flow Loop and Valve Positioner Tips

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Submitted by Greg McMillan on Mon, 02/09/2015 - 20:58
A lot of time and money can be spent deciding which valves need positioners and which flows need measurement. We tend to look at short term costs such as hardware and not the cost of troubleshooting and the implications as to plant performance.

Why Tuning Tests are Not Repeatable Tips

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Submitted by Greg McMillan on Mon, 01/19/2015 - 16:18
Each process test will typically give a different result in the process dynamics identified and consequential tuning settings calculated. Here we look at the sources of this lack of repeatability, the implications, and what can be done to improve tuning tests.

Simple PID Tuning Diagnostic Tips

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Submitted by Greg McMillan on Tue, 01/06/2015 - 23:38
There are some simple diagnostic checks and rules of thumb on tuning adjustments that can be used to find out if there is a problem with the PID tuning and what is the solution. This guidance in conjunction with good tuning software can reduce process variability introduced or aggravated by...

Controller Attenuation and Resonance Tips

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Submitted by Greg McMillan on Mon, 12/15/2014 - 20:18
When is a controller in automatic not able to do anything to reduce an oscillation? When will a controller amplify an oscillation? In both of these cases, the controller is doing more harm than good by wearing out valves and upsetting other loops.

PID Structure Tips

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Submitted by Greg McMillan on Wed, 11/05/2014 - 14:14
Before the 1990s relatively few choices in PID structure were offered. There were also various supplier specific rules as to how to set the proportional mode and integral mode tuning settings to get proportional-only and integral-only control. A different model controller may have been needed for a different structure.

PID Form Trick or Treat Tips

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Submitted by Greg McMillan on Sun, 10/26/2014 - 16:06
Not knowing the implications of the PID Form in an existing control system being migrated or the PID Form learned in a University course can cause gross errors in the tuning parameters and potential instability. The PID Form predominantly used today is not the Form in most of the controllers...

Batch Optimization Recommendations Tips

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Submitted by Greg McMillan on Thu, 08/28/2014 - 19:26
Batch processes pose particular challenges for closed-loop control and optimization due to inherent process nonlinearity and non-self-regulation. At the same time there is a greater potential for increasing capacity in batch than in continuous processes. Solutions need to address the interrelationship between yield, capacity, quality, and repeatability.