Preset values changing

[Scouse_logic]

Be gentle, itÂ’s a first post & IÂ’m learning along the way.
Have checked out this forum and search engines for answers, hopefully someone can point me in the right direction
5562 controller, Rev15.3 & battery is fine.
Had a power outage on a machine, when reset a strange thing happened, timer preset values that had been changed about 6months ago by a specialist reverted back to their original values. The Plc had not lost its program, on changing them back normal operation resumed.

Looking at the program offline, think I may have answered my question, maybe a more experienced person can cast an eye over and let me know if IÂ’m on the right track
Under standard functions there is a first scan, it appears to have all the original preset values in MOV instructions with destinations that match the timers where the values reverted back, as itÂ’s within the first scan, from what IÂ’ve found In the searches this only runs when power is first applied/ after a power outage?

Any guidance will be appreciated
Cheers

 

[Ken Roach]

Welcome to the PLCTalk forum community !

You have almost certainly correctly identified the issue.

There's a pre-defined operating system tag called "S:FS", a Boolean value which is True only during the "first scan" of each Routine that examines it.

First Scan happens at power cycle, or when the controller transitions from Program to Run mode, like with the download of a new user program.

 

[Scouse_logic]

Thanks Ken,
appreciate you taking the time to reply