Generally we distinguish two methods to facilitate a DCS migration; offline and online. A DCS migration has a major impact on the process. The extent of this impact depends on the migration method that is selected. There are many reasons to migrate online rather than offline, three of those are discussed:
Downtime
Downtime is the obvious reason to select an online DCS migration over an offline DCS migration. The benefits of reducing downtime vary for every industry, are specific for each site and are usually the key factor in the decision for an offline or online migration.
This is partly based on the common thought that offline migration is safer and easier, and online migration is only an option if downtime and production loss are unacceptable. Nevertheless, online migration has two more strong advantages that are not always given their full credit.
Trouble shooting
When performing an online DCS migration with the IST-203 Online DCS Migration Tool, loops are migrated one by one. This gives the strong advantage that any problem or mistake in the pre-studies or implementation is quickly identified and located, and can be resolved easily using the online DCS migration tool. During an offline migration, all loops are migrated at the same time (during a short time span). Mistakes might only be discovered after the migration is completed, when the installation is starting or active, making it harder to identify and locate the problem. On top of that, the IST-203 is able to check and verify the loop and the new control system output, facilitating trouble shooting on-the-go and the possibility to step back if a problem cannot be resolved directly.
Small, dedicated teams
An offline migration usually needs to be done in a very limited time span, as every hour of downtime is very costly. To complete the migration in time, a large group of engineers will have to be trained and prepared for the migration, which can be time consuming and expensive. Besides that, using a larger group of engineers with low experience in the field of DCS migrations combined with a high time pressure increases the risk of human failure. Performing an online migration by using the IST-203 Online DCS Migration Tool, small dedicated teams can perform the migration, decreasing the risk of human failure and increasing the consistency of the work.
