Situation
A Victorian food packaging site ran a cartoner and case packer on a controller family no longer supported by the OEM. Spare CPUs were exhausted globally; intermittent memory faults caused unplanned stops twice per month. Production demanded a retrofit inside a single planned hygiene shutdown—roughly thirty-six hours from electrical isolation to first salable pack.
Problems encountered
- Original logic existed only as an uncommented export with no sequence documentation.
- Safety interlocks mixed hardwired relays and PLC bits in ways that were not reflected on drawings.
- Operator HMI was embedded in the legacy platform and could not migrate without rewriting screens.
- Vendor IO modules required custom cabling adapters because rack dimensions differed.
Engineering response
TECHNLOGIX PTY LTD reverse-engineered sequences by observing production runs and logging IO states during changeovers. We produced a state-based functional description signed by maintenance before any code was written. Safety functions were revalidated with the site’s WHS representative; hardwired e-stops remained hardwired, with PLC performing only documented monitoring functions.
Bench testing used a simulated IO rack mirroring address mapping. FAT included fault injection: jam sensors, missing product gaps, and reject gate failures. During shutdown, we migrated in slices—utilities and conveyors first, packaging heads second—so partial rollback remained possible until the final four hours.
Outcomes
Cutover completed inside the window with two minor punch items cleared during hypercare the following week. Unplanned stops tied to the old controller were not seen again over the next two quarters of operation. OEE improved modestly after changeover timeouts were re-tuned with operator input. Maintenance received annotated logic exports and an updated IO list matching field labels.
Lessons for similar sites
Shutdown windows do not forgive missing FAT evidence. Investing three weeks in simulation saved an estimated full shift of on-site debugging. Sites planning similar retrofits should inventory safety relay wiring before quoting—electrical surprises are the largest schedule risk.