FEL is all about minimizing the risk: The cost risk, the schedule risk, and the scope risk for any capital undertaking. Early in a project, the cost impact of changes is low, but it increases, often drastically, in later stages.
Mitigating Project Risks through Front-End Loading for Control System Migrations
![Mitigating Project Risks through Front-End Loading for Control System Migrations](/images/articles/23121.jpg)
Tom McGreevy, PE, PMP, CFSE | aeSolutions
Spend a Little to Reduce the Project Risk
Why Does Anyone do Front End Loading (FEL)?
Rip and Replace vs Phased Approach?
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Perform a piecemeal upgrade of the system by area. For example, a site has multiple controllers in the plant that are geographically dispersed across different plant areas. Perhaps one plant area can withstand a complete outage better than another area or perhaps one area of the plant is suffering more reliability issues due to the old control system. This would be a piecemeal approach or a “mini-rip and replace” over several phases.
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Replace the “top layer”, the servers and operator stations for the entire system. Consideration must be given to the compatibility of new computer hardware and operating systems to the controllers and other interfaces. Virtualization of the new top layer should be given strong consideration, as this topology is certainly the trend not just in industrial control but throughout the IT industry. Then, in a subsequent phase, the controllers and I/O can be replaced by plant area. Note that sometimes old controllers are be replaced but the old I/O is kept in place. The reasons for this may be to reduce the field construction labor and the risk of cutting over the field device wiring during the turnaround. This approach should be very carefully considered as the plant could be left with long-term reliability issues associated with the old I/O.
Another approach to keeping some of the legacy I/O sub-system something I refer to as “The alien approach.” Many may recall a scene from the movie Alien where the creature has its tentacles around a character's face. Similarly, in the alien approach, an adapter and harness are installed on top of old infrastructure, typically at the I/O rack, with the intent to significantly reduce the cutover time of an upgrade. Often such strategies retain a “Marshaling Terminal Assembly” or “Field Terminal Assembly”, which themselves have electronic components that can fail. Thus, the trade-off is living with a portion of the old hardware and an old interface, and the adapter/harness strategy can also limit access to important troubleshooting points.
A Living Functional Specification is a Rare Beast
Managing Expectations
Conclusion
The content & opinions in this article are the author’s and do not necessarily represent the views of ManufacturingTomorrow
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