Updated October 2026.
Compare a retrofit and a replacement on three written answers: interface, validation and downtime. Use the signals, checks and stop window for the station in question.
Keeping a station and replacing a station both need an answer on three topics: the interface, the validation, and the downtime. The answers are not interchangeable. A signal that already leaves the existing controller may have no equivalent on a new machine, and a check that was signed last year may not cover a new assembly.
For a retrofit, write which signals already cross the interface, which document revision describes them, and who owns that document. Then write which checks must be repeated because the change touches them, and which checks stay valid because the change does not. Then write how long the station is stopped, in the plant’s own calendar, including the time to put the old behaviour back if the change fails.
For a replacement, write the same three headings again rather than copying the retrofit answers. The new interface has to carry the signals the next station actually uses. Validation starts from the new machine’s behaviour, not from the signature on the old machine. Downtime includes removal, installation and the time the neighbouring stations wait.
A choice between the two is not a preference for new equipment. It is a comparison of those written answers. If the interface owner is unknown, neither column is ready. If the validation scope is “whatever the vendor says,” the scope is still unwritten. If the downtime window is shorter than the work, the case is a different project and should say so.
Set speed, power and dimensions from the document for this station. A rated speed on a vendor page is that page’s claim; confirm it on the station during the trial. When the station’s mechanical frame and cams are intact but its PLC and servo drives are discontinued, evaluate the 7-point mechanical audit, UL 508A / ISO 13849-1 PL d safety triggers, and 30%–45% cost-ratio math in our PLC retrofit vs. new machine capital expenditure approval reference.
