Moved plants this year and got handed a line nobody documented. Main controller's a 1756 L73 on V31, about 3000 controller scope tags. Names like B3_7, N7_12, Pump2new, Pump2new2, TEMP, and descriptions on maybe a third of them. Converted from a PLC5 years ago and every contractor since has added their own.
I spent two hours yesterday finding which bit stops conveyor 4. Supervisor says fix it, so it's mine now.
I tried renaming online with a prefix per area, got about 40 tags in and the HMI lost half its screens because the FactoryTalk View side still points at the old names. Put them all back by hand, which was my evening gone.
Is there a convention that survives the next contractor, and how do you get there on a line that runs six days a week?
Renaming online is the trap and you found it. Before a convention, what else reads these tags? One HMI, or a historian, MSGs from other controllers, Kepware? Count them, that's your blast radius.
One PanelView Plus 7, and a historian through Kepware, about 400 tags between them I think. No MSGs that I've found yet, but I haven't found everything.
Whoever comes after you will do what the pattern tells them, so make it short enough to type on a Sunday. We ship with Area_Equipment_Signal and a UDT per equipment type. We tried the b_ and i_ prefixes on everything once, looked tidy on paper, nobody kept it up past the first site visit.
Area_Equipment_Signal, like C4_Conv_RunCmd. A UDT per equipment type, so a pump is one tag, C4_Pump2, with .Run, .Fault, .Amps as members, and the pump display takes the one tag as a parameter. Descriptions live in the controller, not in a spreadsheet. No abbreviations that need a key.
Started offline. Exported the L5X, did area C4 in a text editor, imported it into a copy, and it compiles on V31. That part's fine.
The HMI side is where I'm stuck. 400 tags in FactoryTalk View, do I really retype every one?
No. Design tab, open each display, Edit, Tag Substitution, old prefix to new prefix, one display at a time. That's why you lost half the screens, you renamed on one side only. Kepware gets a fresh tag list from the new project. Then one download per area, on a stop. Someone did a decent article on the documentation side: https://plctr.com/best-practices-for-plc-program-documentation/
Area C4 done on Saturday's stop. L5X renamed offline, one UDT for pumps and one for conveyors, Tag Substitution on the eight C4 displays, Kepware tags re-created, downloaded to the L73. Conveyor 4's stop bit is C4_Conv04_StopCmd now and it took me ten seconds to find on Monday.
The mess was no convention and every contractor adding their own, and my own mistake was renaming online. What works: Area_Equipment_Signal, UDTs per equipment type, all of it offline in the L5X, HMI by Tag Substitution, one area per weekend.
The Kepware tags I re-created by hand and there's got to be a better way for 400 of them. Thanks hannah, priya87 and ollyb.
Next contractor won't even notice. That's the goal.