PLC Migration Planning Checklist

This is the checklist I actually work from when a plant decides to pull an obsolete or unsupported controller and drop in a new one. It pairs with the longer blog post on migrating obsolete controllers; that post is the "why and how," this is the one-to-two page working document you print, mark up, and carry through the job. It's written to survive contact with a real plant, whether that's a crusher circuit on an aggregate site, a sort line at a materials recovery facility (MRF), or a digester and gas train at an anaerobic digestion (AD) / organics plant. Rule of the whole exercise: you are not allowed to know less about the plant after the migration than you did before it. If a rung, an interlock, or a setpoint existed for a reason nobody wrote down, that reason is the job.

Safety header — read before any hands-on work ☐ Lock-out/tag-out (LOTO) to a zero-energy state before any hands-on work on the panel, field devices, or anything the panel drives. Verify zero energy at the point of work, don't assume the disconnect did it. ☐ Energized-work caution: if you must take live measurements (loop power, incoming control voltage, comparing states on a running machine), that's qualified-person, PPE, permit work. Put that step behind this warning every time — never bury an energized test inside a routine checklist line. ☐ Stored energy on drives: variable frequency drives (VFDs) and servo drives hold a charged DC bus after power-down. Wait out the manufacturer's discharge time (commonly a few minutes — check the drive's spec/label) and verify bus voltage is down before touching drive terminals. ☐ Rotating / stored-energy equipment: conveyors, screens, crushers, mixers, pumps, augers, and balers can restart or free-wheel. Block, chock, or pin as needed; a gravity take-up or a loaded incline conveyor will move when you release the brake.