Published March 14, 2026 · by Tyler Wray
Names and specifics are scrubbed at the customer's request, but the shape of the project is typical for any 1990s-era huller still running an SLC-500 in 2026.
What we walked into
Original installation was Allen-Bradley SLC 5/04 over DH+, three I/O racks, an early PanelView 1000 that had been replaced once with a PanelView Plus 700, and a tangle of intrinsically safe barriers in the dust zone that had been added piecemeal over twenty years. Two of the racks had counterfeit replacement modules that the customer didn't know about.
What we replaced
- PLC: SLC 5/04 to CompactLogix 5380 with a redundant power supply.
- Network: DH+ to EtherNet/IP on a managed Stratix switch.
- I/O: full Point I/O replacement with proper IS barriers re-rated for the current dust classification.
- HMI: PanelView Plus 7 with FactoryTalk View ME, ported screen-for-screen on day one, then iteratively cleaned up over the off-season.
What we kept
Field devices, motor starters, the main MCC, and most of the conduit runs. There was no reason to touch any of it and pulling new wire through a working huller is a great way to extend a four-week shutdown into ten.
Surprises
Two. First, the original DH+ network had a ground loop that had been masked by the old hardware's tolerance — modern Ethernet hardware exposed it immediately and we spent a day chasing it. Second, the historical alarm log lived only in the old PanelView's volatile memory. We pulled what we could before swap-out and warned the customer that the first year's historian data would effectively start from scratch.