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    Choosing Between PLC Migration and Upgrading: Selecting the Optimal Path

    You're faced with a challenge: your trusty old PLC, like the Allen-Bradley PLC-5, has dutifully served you for years, but now it's no longer supported. The manufacturer no longer offers maintenance or spare parts, leaving you in a predicament if something goes awry. Beyond the potential downtime, the escalating costs of replacement parts in the secondary market prompt a question: is repairing this outdated PLC worth it?

    Typically, the answer is no. However, once the decision to transition to a new PLC like the ControlLogix is made, the journey is far from over. As you reshape your systems, you need to consider the extent of change. This is where two paths diverge: migration or upgrading.

    This article guides you through key factors to help you make an educated choice. We'll begin by outlining the contrast between migration and upgrading, followed by exploring the pros and cons of each approach.


    Migration vs. Upgrade: A Brief Explanation

    In simple terms, migration involves directly translating a previous control system to a new one, while upgrading introduces novel features, modernizations, or innovative technologies. Migrations aim to maintain as much similarity as possible, ideally ensuring an imperceptible difference. Upgrades, on the other hand, strive to enhance productivity, drive efficiency, foster a safer work environment, or achieve similar objectives.

    Distinguishing migrations from upgrades hinges on the treatment of the PLC code. For migration, code conversion software like Rockwell's RSLogix Project Migrator is employed, automating the translation of existing logic into code for the new PLC. While these tools aren't flawless, they offer the swiftest way to transition old ladder logic to new hardware. Conversely, upgrades entail crafting new code from scratch.

    Another contrast is in handling I/O wiring. Migrations aim to preserve current wiring by plugging them into an I/O card attached to the new PLC. In contrast, upgrading necessitates more extensive I/O reconfiguration, affording the opportunity to rewire components during system updates. Essentially, migrations minimize overall changes throughout the plant.

    In either case, a meticulously planned transition limits downtime to an acceptable maintenance window. Naturally, given the intricacy of upgrading, longer windows might be expected, potentially requiring a phased approach where each element is upgraded sequentially. For example, you might initiate by installing and coding the new PLC, then proceed to upgrade the HMI, and finally rewire the I/O.

    Pros and Cons

    Having grasped the contrast between PLC migration and upgrades, let's step away from the technology itself and delve into the business perspective. The decision between these two options ultimately rests on a high-level strategy, informed by the company's distinctive circumstances. Although we can't definitively advise which path to take, we can equip you with tools for sound decision-making.

    Let's start with the merits and demerits of migration. One advantage of migration is its reduced upfront cost. Lower downtime, fewer new hardware expenses, and reduced time spent writing code and designing infrastructure collectively make migration a more cost-effective endeavor.

    Secondly, migrations entail less immediate risk. Perfectly flawless software is an illusion, particularly within intricate control systems. Whenever new code is written, inherent risks are embraced. For risk-averse organizations, particularly those operating 24/7 or with stringent production uptime prerequisites, this might tip the scales in favor of migration.

    Another plus of migration is its familiarity for operators and technicians. Although a learning curve is anticipated for using, troubleshooting, and repairing the new PLC, this transition is less significant than acclimating to an entirely new system. In essence, migrations facilitate shorter training periods and diminish the likelihood of operator errors when relying on "autopilot."

    Nevertheless, migration isn't devoid of downsides. One crucial factor is that contemporary PLCs have distinct architectures from their older counterparts, rendering a seamless 1:1 transition unattainable. Rockwell underscores that "PLC-5 and SLC 500s are based on 16-bit architecture, while a Logix controller relies on 32-bit architecture and supports a 1-millisecond time base."

    These disparities can lead to unexpected runtime errors and pose a significant hurdle when translating old logic into new code. Migration is seldom a linear process and, in certain scenarios, it might prove infeasible.

    Another drawback of migration is heightened long-term risk. This becomes particularly pronounced when integrating new machines onto the factory floor. Automatic code conversion tools seldom yield tidy code that's easily modifiable. In fact, the resulting code often lacks clarity, is arduous to decipher, and proves an ongoing challenge for maintenance teams. Additionally, both the new tag names and data remain convoluted, adhering to outdated PLC-5 conventions that aren't compatible with new PLCs.

    Consequently, revisiting the code for improvements or adding logic, such as for a new robot, becomes significantly arduous. In essence, migrations are less future-proof than upgrades.

    Turning to upgrades, the pros and cons are essentially the reverse of migrations. True, they entail higher initial costs, introduce short-term risk, and necessitate operators' proficiency in utilizing and maintaining the new system.

    However, by implementing modernized infrastructure, upgrades open avenues for harnessing Industry 4.0 technologies such as the Industrial Internet of Things (IIoT), cloud computing, and machine learning (ML).


    So, what's the best course of action? Should you fix what isn't broken? A white paper by Schneider Electric asserts that "while playing it safe may have sufficed in the past, the accelerated pace of business today renders complacency an untenable strategy."

    While technological innovation is undeniably advancing swiftly, the decision between adaptation and lagging behind isn't the entire narrative. Certain industries thrive on a less-is-more approach, whether due to stringent regulations or the industry's nature.

    This is where the dialogue commences. Our panel of experts can guide you in determining the ideal path for your distinct circumstances. Whether that involves a basic migration, a complete upgrade, or a hybrid strategy involving a migration followed by phased upgrades, Outlier leverages its expertise to ensure you're making the right decision.

    Ready to engage? Reach out to us today, and keep an eye out for the follow-up article delving deeper into the upgrade process.