May 1, 2025
Modernising Legacy Control Panels: A Strategic Approach for Food, Beverage, Pharmaceutical & Manufacturing Industries
The Challenge of Ageing Control Systems
Many production facilities continue to rely on decades-old programmable logic controllers (PLCs) and control panels. These legacy systems often struggle with obsolete hardware, poor diagnostics, and limited functionality, forcing maintenance teams to improvise solutions. Ageing controllers typically suffer from reduced processing power and an inability to integrate with modern devices, while spare parts become increasingly difficult to source as industry experts note that the primary cause of control system failures is simply the obsolescence of parts and equipment.
Unsupported devices like Allen-Bradley SLC-500 or Siemens S7-300 may continue to function, but they lack modern diagnostics, data connectivity, and vendor support. As these challenges compound, upgrading or retrofitting these systems has become a necessity rather than a luxury for facilities aiming to avoid unplanned downtime and operational inefficiencies.
Benefits of Control System Modernisation
Modernising your control systems offers numerous advantages that directly impact your bottom line:
Enhanced Performance and Reliability
Replacing old PLCs with next-generation controllers brings advanced features: on-board diagnostics, real-time analytics, remote monitoring, and higher processing speeds. Modern controllers have faster processing capabilities and scan rates, allowing for tighter control loops and quicker responses to process changes. This often translates to immediate performance improvements, with machines running closer to optimal limits and reactions occurring more promptly.
Improved Data Access and Visibility
With modern Ethernet-based I/O and SCADA (Supervisory Control and Data Acquisition), operators gain access to far more sensor data and historical trends, helping identify faults before they cause outages. Every new I/O tag or networked sensor adds visibility into your processes, providing valuable data that can be used for analytics, reducing scrap, optimising recipes, or detecting faults before equipment fails.
Energy Efficiency Gains
New PLCs and process controllers can actively manage power use (for example, modulating drives and pumps based on demand), yielding significant energy savings through tighter control. These efficiency improvements not only reduce operational costs but also support sustainability initiatives.
Enhanced Regulatory Compliance
For regulated industries like pharmaceuticals and food production, upgraded control systems improve compliance capabilities. Modern systems can include batch tracking, electronic signature logs, and alarm audits—features that older analogue panels simply cannot provide. This enhanced data logging and alarm-trending help meet FDA/ISO records requirements without manual workarounds.
Simplified Maintenance and Support
Unlike obsolete platforms, new PLCs come with active vendor support and readily available replacement components. Maintenance teams no longer need to hunt for rare modules on secondary markets, as spare parts are stocked by distributors. Additionally, because programming tools are current, finding technicians to work on the system or training staff becomes significantly more straightforward.
Effective Retrofit Strategies
Upgrading a control panel doesn’t necessarily mean replacing an entire production line. System integrators employ several approaches to modernise with minimal cost and downtime:
Like-for-Like Upgrades
This approach involves swapping an old PLC for a modern equivalent (or updated model) while keeping the existing programme logic structure. For example, replacing a PLC-5 with a ControlLogix can be done using migration tools to preserve ladder logic. This is cost-effective when systems are small and only the CPU is outdated.
Platform Migration
This strategy moves an entire system to a new controller family. Common examples include converting Allen-Bradley SLC-500 or PLC-5 racks to CompactLogix/ControlLogix, or Siemens S7-300 to S7-1500. This may involve rewriting some code, but tools like RSLogix Project Migrator can automate much of the conversion. Field I/O can often be preserved by mapping old modules to new I/O racks to reuse existing wiring.
I/O Preservation
When controllers change, existing field wiring represents a valuable asset. Retrofit kits or migration modules typically allow mounting new I/O cards in place of old ones. Some approaches also include using remote I/O devices to move intelligence closer to sensors, reducing panel complexity while preserving wiring investments.
Hybrid and Phased Approaches
For large plants, engineers may combine old and new equipment. Critical loops can be moved to the new system first while leaving the rest running, then cut over gradually. This staged migration lets production continue and spreads cost over time. In some cases, an Ethernet communication card can even convert an old PLC rack into remote I/O, preserving the majority of the system until a full upgrade is ready.
Reverse Engineering Logic
When original documentation is missing, engineers must reconstruct or translate old code. For undocumented custom logic, teams map inputs/outputs and test latches or timers manually. By comparing legacy code to similar processes, they can rebuild functionally equivalent modern PLC programmes—an essential process when source files are lost or old software cannot be read directly.
The Engineering Workflow
A structured engineering process is key to executing a smooth retrofit. The typical workflow includes:
Site Assessment
The integrator conducts a thorough inventory of existing PLC hardware, I/O modules, and network devices, gathering any available documentation (control narratives, wiring diagrams, HMI screens, etc.). This often involves on-site I/O mapping—tracing which field device connects to each panel terminal—and interviewing operators to understand manual overrides or interlocks.
Design and Configuration
With assessment data in hand, engineers select new controllers, I/O, power supplies, and other components that match requirements. They prepare panel layouts and schematics following the client’s electrical standards and develop the PLC/HMI code. If migrating to a different platform, conversion tools or manual coding are applied at this stage.
Offline Testing
Much of the new system is assembled and tested offline in parallel with the old system. New panels or cabinets are fabricated and wired to match the planned I/O count. All components (PSUs, controllers, HMIs, network switches, etc.) are powered up and verified in a factory acceptance test (FAT) environment. This critical phase ensures wiring or device errors are identified early, and control logic is debugged before on-site implementation.
Commissioning and Cutover
During the agreed shutdown window, technicians install the new hardware, migrate I/O as planned, and perform a Site Acceptance Test (SAT) on the live plant. Extensive pre-planning minimises plant downtime. After all loops are transferred, the new system is started up, with engineers verifying each interlock and control sequence and training operators on the updated interface.
Control Panel Upgrade Components
A panel retrofit typically involves refreshing multiple hardware elements:
Power Supplies and Cooling
Replacing ageing power supply units with higher-efficiency models and adding fan trays or vents for proper cooling. While modern LEDs and power supplies generate less heat, proper thermal management prevents failures.
Contactors and Relays
Many older panels use electromechanical contactors or relays for motor starters. These may be replaced with newer models or solid-state equivalents to improve reliability. Safety-rated starters or drive bypasses can be added during the upgrade if needed.
I/O and PLC Modules
Old rack I/O modules are swapped out, sometimes using migration kits that allow drop-in replacement of new I/O into existing chassis. Digital and analogue I/O count is verified against field requirements, with extra unused points closed out or repurposed. Remote I/O networks may be introduced to decrease wiring and expand coverage.
Networking and HMI
Often new Ethernet switches and cabling are installed. Legacy serial links are replaced with industrial Ethernet or fibre optics. HMI/SCADA computers are upgraded, with screens redesigned in a modern environment for consistency and improved data logging.
Safety Systems
Where required by regulation, safety relays or dedicated safety I/O modules (with redundancy and diagnostics) are added. This allows for the integration of emergency stops, light curtains, or door interlocks with proper certification.
Minimising Downtime During Upgrades
Downtime is the enemy of any retrofit. To keep production running, companies use strategies like parallel builds and staged cutovers. New panels are fabricated off-site (or in a separate room) so the existing line can run until the last moment. Once the new system is ready, it is brought online during a planned outage—often a weekend swap.
Some installations use a “swing-arm” approach, temporarily mounting new hardware in the same rack to wire it in advance. Others cut over one area at a time, running both old and new controls in parallel on separate channels (a “hot cutover”).
In one reported project, over 800 I/O points were cut over on the first day of a three-day shutdown, thanks to extensive pre-assembly and off-line testing. This kind of disciplined, parallel approach enables plants to achieve near-zero unplanned downtime during retrofits.
Real-World Success Stories
Pharmaceutical Manufacturing
One pharmaceutical plant upgraded its entire 1985-era control system to a modern PlantPAx/DCS platform. The project included rewriting all PLC code and replacing analogue loop controllers, and was completed with just five weeks of planned downtime.
Post-upgrade, the system generated daily production reports and provided historians for the first time, giving operators actionable data and enabling predictive maintenance. Technicians gained remote diagnostic capability, and improved parts availability and support meant much faster recovery from faults.
Food & Beverage Production
In the food & beverage sector, a UK snack manufacturer needed to triple throughput to meet demand. The integrator installed a new Siemens S7-1500 PLC and Profinet network for the packaging line, replacing several legacy PLCs and motor controllers. The result was a 50% capacity increase and a unified control system with recipe management.
Crucially, the swap was done in a phased upgrade that did not halt production: teams pre-wired panels and cut over drives over a short weekend. The outcome was “minimal downtime” and on-time delivery of the project, despite the significant performance boost.
In another dairy example, a plant’s pasteuriser and evaporator—originally controlled by dozens of standalone PID controllers and manual valves—were automated with a new PLC system. The upgrade centralised control, removing hundreds of relays and PID loops and replacing them with unified logic, resulting in improved consistency and higher yield while retaining the existing process equipment.
Our Turnkey Modernisation Approach
Our company delivers comprehensive modernisation projects from start to finish, with a focus on minimising disruption to production. Our process includes:
- Complete Site Survey: We inventory existing PLCs, I/O, and network devices and gather all available documentation.
- Detailed Upgrade Planning: We draft a comprehensive upgrade plan, specifying which controllers, I/O modules, and other components will be replaced or reused.
- Off-Site Building and Testing: We assemble upgraded control cabinets in our workshop, wire them according to the latest drawings, and execute full factory acceptance testing.
- Co-ordinated Cutover: We work closely with plant management to schedule cutovers during planned shutdowns or low-production periods, often using parallel-run strategies.
- Comprehensive Training and Documentation: We train operators on the new interface and provide complete documentation for the upgraded system.
By packaging the project end-to-end, we minimise surprises and ensure nothing is left undocumented. The result is a future-ready control system with faster processors, full data connectivity, and ongoing support—all without requiring a full plant replacement.
Conclusion
Retrofitting legacy control panels represents a strategic opportunity for food, beverage, pharmaceutical, and general manufacturing facilities to boost efficiency and competitiveness. With thorough planning, off-line building, and smart cutover techniques, these upgrades can be delivered on schedule with minimal impact on production.
The result is better performance, fewer faults, and the data visibility needed for Industry 4.0 initiatives—all accomplished without scrapping entire production lines. As obsolescence challenges continue to grow for facilities with ageing control systems, modernisation offers a cost-effective path to improved reliability, efficiency, and compliance.
Contact us today to learn how we can help you modernise your control systems with minimal disruption to your operations.
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