The case for upgrading legacy control systems
End-of-life PLCs are a production risk. Spare parts become unavailable, software licences expire, and the engineers who understood the original system move on. When a legacy PLC fails, the options narrow fast - and unplanned downtime on a processing plant is expensive.
The case for a planned upgrade is straightforward: do it on your schedule, in a controlled way, with time to test properly and train operators. Not in response to a failure at 2am during a production run.
We understand that upgrades involve risk and cost. Our job is to manage the engineering so the risk is as low as possible and the cost is justified by what the new system delivers.
What a control system upgrade involves
System audit and documentation - before any upgrade work begins, we document what the existing system does. Existing programs are read and a functional description produced. I/O lists, network topology, and interlocks are confirmed against what’s actually installed. This is often the most valuable part of the project - it surfaces undocumented workarounds and process knowledge that would otherwise be lost.
New system design - hardware selection, panel design, network architecture, and program design for the replacement system. We specify hardware that is current, well-supported, and appropriate for your site environment.
Program development and testing - new PLC code written to match the documented functional requirements, with improvements where the old system had known deficiencies. Factory acceptance testing (FAT) in our workshop before any site work begins.
Cutover planning - detailed sequence for the shutdown cutover, including decision points, rollback conditions, and resource requirements. Shared with your operations and maintenance teams before the shutdown starts so everyone knows the plan.
Site installation and commissioning - hardware installation, cable termination, loop checking, and commissioning during the planned outage. We work to your shutdown schedule and communicate clearly when milestones are hit or slipping.
Handover and training - program documentation, as-built drawings, and operator training at handover. Your maintenance team should be able to work on the new system without calling us for routine tasks.
Common upgrade projects
Rockwell PLC-5 and SLC 500 migrations are the most common upgrade we see across Queensland. These platforms have been out of production for years and spare parts are increasingly difficult to source. Migration to ControlLogix or CompactLogix preserves the I/O footprint while moving to a supported, current platform.
GE/Emerson Series 90 to PACSystems RX3i migrations follow a similar pattern - often complicated by the fact that legacy GE documentation is poor or nonexistent, requiring more upfront audit work before the new system can be designed.
Schneider Modicon Quantum to M340 or M580 - Quantum hardware is end-of-life and spare parts are scarce. Migration to M340 or M580 in EcoStruxure Control Expert (formerly Unity Pro) preserves the Modicon architecture while moving to a current, well-supported platform with available hardware.
Omron CPM1A and other legacy Omron platforms migrated to current Omron NX/NJ series or cross-vendor equivalents where site standardisation requirements permit. CPM1A systems are commonly found on small, isolated plant control applications where they have been running untouched for decades.
Siemens S5 and older S7 platforms - S5 systems are significantly past end-of-life and require full re-development of the control program rather than direct migration. Older S7-300 and S7-400 systems are approaching end-of-production support and are increasingly subject to migration planning.
Older sugar mill and water utility control systems frequently involve mixed-vendor environments with multiple legacy PLCs, ageing SCADA, and communications infrastructure that predates modern industrial networking. These projects require careful phasing to keep the plant running while the upgrade progresses.
SCADA platform migrations
Control system upgrades frequently include or trigger a SCADA migration - the PLC hardware change is the planned outage event, and the SCADA upgrade is scoped to run in parallel so both layers are current after the cutover.
CitectSCADA v7.x to PlantSCADA 2024 - the most common SCADA migration we scope for Queensland mining and sugar sites. The project structure is broadly compatible but migration requires device driver review, graphics library assessment, and a Cicode audit before the cutover can be planned. Running CitectSCADA v7.x on current Windows versions is increasingly difficult as OS compatibility narrows.
FactoryTalk View SE version upgrades (v7 to v12+) - Rockwell FactoryTalk View SE version upgrades are not always straightforward. Display graphics, tag database references, and HMI server configuration may require rework between major versions. We scope FactoryTalk upgrades carefully, testing the migrated application against the existing tag database before any site work begins.
Wonderware migrations - Wonderware InTouch and System Platform installations on legacy versions of Application Server or System Platform require re-engineering rather than a direct version upgrade in most cases. We assess the existing Galaxy database, object model, and InTouch application against the target version and scope a migration that preserves the operational functionality while moving to a supported platform.
Planning for minimal downtime
The majority of upgrade work happens before the shutdown. Hardware is staged, programs are built and tested, and documentation is complete before the outage window opens. The shutdown itself is used for physical cutover - disconnecting the old system, connecting the new one, and commissioning.
This approach - thorough preparation, disciplined cutover execution - is what keeps upgrade projects on schedule.