• Legacy Control System Migration Part II

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In Part I of our series, we discussed the definition of legacy controls migration and the reasons it has become a critical issue in many plants. This segment will address other issues related to implementing such a migration strategy. Developing a Migration Plan: Complete vs. Partial Although an immediate full migration would be the most effective remedy for addressing antiquated controls, it is not always feasible for the plant/owner. The migration also can be completed in various segments. The two basic issues impacting the decision to do a complete or a phased migration are as follows:

  • Cost: What can you afford to spend within a specified budget cycle? A phased approach allows for smaller cost chunks.
  • Time: Are productivity, efficiency, or regulatory issues forcing completion within a given time frame, or are timeframes more open-ended?

When planning for systems migration, the best time to perform the migration should be established as well as the best migration path, along with goals that are clearly defined. The migration process should be defined through front-end engineering with a comprehensive checklist and detailed cutover plans. Operability and training plans also should be established. This means pinpointing who will be affected by the change as well as identifying available resources and contingency resources in the event they are needed. The migration plan should clearly define whether a phased migration or a complete replacement will be completed. A phased migration allows the system to gradually be updated in steps over time while still benefitting from the partial changeover by taking advantage of improved operations and safety. When dealing with a large-scale retrofit, a phased system migration has some benefits such as eliminating some elements of risk through change of a gradually narrowing focus, while still having the old system to fall back on. However, there are drawbacks including time. If a phased migration is chosen, specific details about how to replace the system in phases should be determined. Systems should be broken down into subsystems so they can be treated in isolation. The design should allow for the migration to be completed as separate projects but also so each segment can be joined together as one fluid system. Understanding Data Flow in Making Migration DecisionsUnderstanding the way data flows is paramount when making migration decisions. A system can be visualized as these four layers:

  1. Global--Current and future client needs. Example: Population growth, financial constraints, rules and regulations, security, and managerial reports.
  2. Interface--The user interface. Example: Supervisory Control and Data Acquisition (SCADA) interface.
  3. Control--The process. Example: The mixing process for flavored milk.
  4. Hardware--Includes equipment, cabinets, Programmable Logic Controllers (PLCs), computers, instrumentation and physical locations. Example: Pumps, flow meters, and switches.

Knowing how the data flows between each of these layers, as well as identifying any constraints, is essential to successfully implementing migration of controls and to make informed choices about how, when, and why to modernize automation equipment. Choosing a Systems Migration PartnerParamount to choosing the right partner to help a plant or operation make the systems migration is having a good working relationship. Both the control vendor and the operations personnel must be able to work as a team during the migration itself as well as in the pre- and post- migration phases. If a vendor plans to merely make the installation and then sever ties, a plant or operation should think carefully about choosing a different partner for this important system upgrade. The procurement process should be two tiered. It should start with developing a stringent qualifications statement that must be met prior to submitting a bid. Some issues that could/should be considered to be addressed in the qualifications document are as follows:

  • Experience: Does the CSI (control system integrator) have legacy migration project experience, particularly for the type of migration path you've chosen? And how experienced are they at implementing projects without interrupting plant operations? Experience needs to address all aspects of a migration project: design specification, functional specification development, configuration programming, panel design and build, acceptance testing, and startup and checkout services.
  • Certification: Is the CSI certified by the manufacturer(s) to work on the equipment you have in place and the equipment you plan to migrate to? If not certified, do they have sufficient experience?
  • System testing: Does the CSI perform simulation testing of all system elements prior to shipping the equipment, or do they expect to wait until installation to do testing? The latter approach can result in much higher installation costs and a much longer installation process.
  • Self-performance of electrical work (if such is required): Is the CSI qualified to perform the electrical installation work (a design-build project delivery method), or will that be subcontracted out. The latter approach may incur additional costs and delays.
  • Documentation: What types of documentation will the CSI provide? Inadequate documentation will make future work on your system difficult and/or expensive. If possible, review samples.

Any company that doesn't meet the specifications should be disqualified from submitting a price estimate for the system migration. This, however, means an owner must do due diligence to conclude whether companies meet the qualifications. The vendors that fit within the defined parameters should only then be permitted to propose estimates and a work plan on the project. Other questions that should be asked include what a vendor's plan is to keep a project running smoothly and how it handles problems, if they arise. Also worth determining are the business values and ethics the potential business partner holds as well as whether there are any warranties associated with the systems migration. Conclusion Regardless of your industry, your plant is probably facing pressures to be more efficient and more productive without increasing the number of staff.  And if your control systems fall into the legacy category, you have probably already experienced how difficult this can be in a legacy system environment. Making processes more efficient through technology can help solve this problem. Although less recognized as a reason, the safeguarding of the loss of critical operational experience can be prevented through updated controls from a systems migration. With today's aging workforce, as staff retire, their experience retires with them.  To mitigate that knowledge loss, defining and upgrading a process can make a company immune, or at least resistant, to staffing issues. As legacy control systems reach the end of their useful life, it is necessary to migrate these older controls to updated, automatic control systems for efficiency, security, retention of intellectual property and to remain competitive in the business arena.

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