Most discussions examining distributed control system (DCS) migration projects concentrate on the early planning stages or the potentially contentious issues of vendor selection. Those are important topics, but if a project runs its full course, at some point, the shiny new automation system will arrive at the plant, waiting to be installed and started up. The risk during the entire installation process, particularly the cutover from the old automation system to the new one, is enormous, with the potential for production to be affected either for good or ill. This is where the rubber meets the road.

A well-planned project should have a detailed roadmap for implementation. If your company already is working with a system integrator or an automation system vendor, the steps of the cutover should be thoroughly outlined and scheduled. If they are not, or if you are still planning, let's look at what must be included in the cutover.

The cutover is the point where the parts of the larger automation system designated to remain in place are moved to the new platform. These typically include field instrumentation, valves, motor controllers, and so on—with all the supporting networks and wiring. These components interface with the system via input/output (I/O) cards, and every connection must be moved from the old platform to the new one. 

Steps prior to DCS delivery

Cutover is the final chapter of the project, so, by the time the new DCS is delivered to your facility, this work should have been done: 

1. Documentation for the facility or unit reviewed and updated
2. Field devices, supporting wiring, and all labeling should be examined, evaluated, and repaired where necessary
3. Factory acceptance test (FAT) of the new automation system performed and passed
4. Supporting infrastructure for the new automation system in place and working.

These four points cover a lot of ground, so let's consider their impact individually. 

1. Documentation can make or break a migration project. A successful implementation depends on having a detailed, complete, and accurate picture of the existing facility. When a DCS is replaced, the facility will have gone through many changes and various updates since the older automation system was installed. If the documentation does not reflect all those changes, problems will emerge at many stages of the migration project. If gaps remain after the earlier stages of the project, they will certainly emerge during the cutover when it becomes necessary to find individual connections, one-by-one, and execute connection changes flawlessly.

During the project, the documentation should be reviewed in detail. This includes: 

• Piping and instrumentation diagrams (P&IDs)
• Loop sheets
• Panel drawings
• Rack room drawings
• Cable and conduit schedules.

If your company is bringing in a system integrator or other outside help for the cutover, it is critical that the team leader performs an audit of the documentation at some level. The degree of detail will vary according to the situation, but much depends on the documentation, so its accuracy should not be taken for granted.

2. Field devices and their supporting wiring should be verified: 

• All devices are in the location shown on the P&ID
• The devices are working correctly
• They are wired as shown
• The wires are terminated in the marshaling cabinets and I/O card where indicated with correct labels (see Figure). 

3. The FAT will have been completed before the system is shipped to the field, and what happens during this step merits its own article. Suffice it to say, by the time the cabinets and racks reach your facility, the control software and hardware should have undergone extensive examination by the vendor and the project team. If the testing was done correctly, there should be no surprises, such as bad I/O cards or hardware glitches.