Converting control systems: Take the time to improve control strategy
One of the most frustrating expressions I see in scope documents is, “Convert the existing control system as it is. We’ll make control strategy improvements later.” It’s painful to see. In my 24 years in systems integration, I’ve learned that later never comes.
It’s easy to understand the appeal of convert-it-as-it-is scopes. First, we know the existing system is working—mostly; where it’s not exactly working, everybody’s already used to it. Second, it’s an easy scope to sell to the business—the existing system is working (mostly) and the new system will be working the same way after the migration. Third, it’s an easy scope to write.
Don’t get me wrong. Clear scopes are crucial for successful projects. Unfortunately, a convert-it-as-it-is scope can rob a migration project of much of its value.
A newer control system is sure to provide one thing—new functionality not available in the existing system. Investing the time to write a scope that includes control strategy improvement opens the door to taking advantage of that functionality. Processes that can be controlled more stably through better control strategies can be optimized. They can be run closer to their limits without causing trips. Operation with less variation can lead to increased production, consistently on spec products, or possibly both.
Developing a plan for process improvement takes pre-project work, often described as front-end loading (FEL). FEL efforts include process studies that identify problem areas, such as that control loop that has run in manual for the last 10 years, or that distillation column that goes out of whack every time it rains. Field surveys determine the state of existing instrumentation so that deficiencies can be addressed, and the new control system will not be hampered by inadequate field devices. FEL work will also provide an improved estimate of project cost.
It may seem that FEL just adds additional cost to a project, but it really adds value for the money spent. Preliminary engineering and design work done in the FEL stage can be immediately rolled into the project. Fleshing out the scope, including instrumentation upgrades, leads to lower risk of project overruns and unpleasant mid-project surprises.
A control system migration is a rare opportunity, one not to be wasted. A project provides money, resources, and support from the business in ways that are not available during ordinary operation.
Working on a project team allows people from operations, engineering, and maintenance to work together on solving problems in ways not usually possible. Once the project is over, the team will disperse. The only people left to make control strategy improvements will be the ones also responsible for day to day plant operations. Guess which will take priority?
Don’t rely on making control strategy improvements later. Later never comes.
Are any of you in the interesting situation of scoping a system migration?
This post was written by MayAnn Stroup. MayAnn is a senior engineer at MAVERICK Technologies, a leading automation solutions provider offering industrial automation, strategic manufacturing, and enterprise integration services for the process industries. MAVERICK delivers expertise and consulting in a wide variety of areas including industrial automation controls, distributed control systems, manufacturing execution systems, operational strategy, business process optimization and more.