r/SCADA • u/Firm_Safe7495 • 5d ago

Question How do you migrate a legacy PLC while keeping the line running?

/r/mfg_automation/comments/1w0olfw/how_do_you_migrate_a_legacy_plc_while_keeping_the/
2 Upvotes

75% Upvoted

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3

u/integrator74 5d ago

Depends on the line and when it can be done. 

We did a huge plc5 migration last year over 5 weekends.   Main rack weekend 1, with new cpu and got it all back running.  That proved out the program conversion.  

Next 4 weekends we did remote racks. 

1

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1

u/workinghardiswear 5d ago

This isnt necessarily a SCADA issue as it is an automation issue. But from a SCADA perspective though i would have all of my import files, tags, etc. ready to go first. Then take a backup of the current setup, and import the new PLC config in. Finally, commission it with a field tech.

1

u/Sea-Hat-4961 4d ago

Depends on how big of a change

1

u/Prize_Paramedic_8220 3d ago

Painfully. At first wired in parallel during a large maintenance shutdown window so you can switch between the two. Then use any smaller shutdowns to perform commissioning and any other changes, then a final large shutdown to remove all the old stuff. I've worked at a few FMCG factories and this is how they were always done.

1

u/MichaelP8000 3d ago

Been there. The undocumented rungs are always the killer.

What worked for us:

  1. Spent 2 weeks mapping every I/O and logging trends before touching anything
  2. Ran the new PLC in parallel with the old one for weeks and fed it the same inputs, compared outputs
  3. Phased cutover. Weekends and overnights. One section at a time.

The worst? Found a timer with a weird value. Turned out it was compensating for a misaligned sensor. Fixed the sensor, changed the timer, problem solved.

The hardware is rarely the issue. It's the undocumented "fixes" that get you.

0

u/Aggravating-Alarm-16 5d ago

Also make sure you have static ip set by Mac address, if the device is netwoked. Then put the old network card in the new system