PLC Version Control

If we are talking about one big binary files, then a VCS (centralized or decentralized) is not the best tool for the job.
An external referencial (a shared disk for instance) where a batch will copy and label the current PCL state is better.
See "Tracking Software History"

To avert discontinuities in the historical record of revisions, old versions of programs must be stored.
“We take it a step further, though. Using our MDT AutoSave, we actually go out and interrogate the equipment. Overnight or at whatever frequency is specified, the software reads the programs in the PLCs and then compares that information to the last known program. The version-control software will copy the new program and store it and [then] compare it to the last one.

Launching version control is fairly simple. Required is software installation and then hardware configuration. “You would need a server and a couple of weeks of engineering and you’re good to go,” Perysyn says. However, his company uses a “shrink-wrap approach” that involves installing the software and then customization by users filling in the blanks.

That being said, when you have multiple changes from multiple developers, you need an integration environment where a first delivery can be done and validated, before pushing it to the actual server.

See also this post.

You need specialized versioning system for PLCs like VersionDog.

From the manufacturer:

"Special support with Smart Compares for SIMATIC S5, SIMATIC S7, SIMATIC PCS 7, WinCC, WinCC flexible, InTouch, CoDeSys, TwinCAT, Phoenix PC WORX, RSLogix, Schneider Modsoft, Schneider Concept, Schneider Unity, SINUMERIK 840D, Bosch IndraWorks and more. Also robot programs from ABB and Kuka and office related data formats like Microsoft Word, Microsoft Excel and Adobe PDF are perfectly supported by versiondog.

Update: Here is a screenshot showing ladder version compare. I guess that's what most PLC folks are interested in. We also use it to schedule e-mail report if PLC offline and online application versions are a match, as an alarm that something has been changed in PLC but not put into version control server.

About RSLogix5000 specifically, I have seen developers use an emulated PLC and make their changes online. The final product once developed is then put together with all the comments (as they are not contained in the PLC) and then commissioned. There are issues with changes that cannot be done online, such as AOIs. There are tools in place to stop two people editing the same logic online at once and to take ownership of sections. Backups can be done in the form of uploads, but there isn't any way to track changes.

It is a messy problem, messier still for when you are maintaining a system as you want an .ACD that you can go online with, as unless you are somehow doing a diff with the RSLogix compare tool you just see unreadable machine code like "+|Éû³´¬ÙÆW×晵‚>Ù,"

The most common revision control I have seen (sadly) is just saving the the latest file, then taking a copy and adding the current date to the file name, like the recommended control.com post described.

I use Unity Pro, so this may not apply for other brands.

Unity can export an "archive" file which is XML which describes the PLC program and IO setup in its entirety. After commissioning changes, I create an export and check it in to my local Git repo. This gets me an annotated history of changes, but no visual comparison. I can always use UnityDiff for comparison.

Check out http://www.mdtsoft.com/ also