ST768 Question and some "Interesting" Behavior

[Dean]

Monday morning I happened to notice that the time on a C-More HMI was an hour slow. The HMI is tied to a Do-More with the attached two rungs to deal with DST. It has worked flawlessly for the last two years. I opened Designer, and sure enough ST768 was Reset. Luckily I log a bunch of data on the HMI so I was able to pinpoint exactly when it happened, Oct 9th 7:35AM (Obviously nobody is using this clock, or if they are, they are just glancing at the minutes value). The logged data timestamps jump from 7:35, to 6:36, with no other hiccups, and goes along its merry way. If I understand correctly, the ST768 is retentive by default, and appears to be set as such in the program. In any case, it has survived a number of other power cycles and retained its value. What am I missing?

[Dean]

The interesting behavior investigation is complete. This HMI also has a set of buttons to Set or Reset DST manually on a password protected configuration screen, and what I was missing were the large fingers of an associate who "may have accidentally" hit the Standard Time button. I really didn't want to put those buttons in there, but the boss didn't want to have to get one the technicians to fix it in ladder if the time ever got screwed up, which until somebody messed with the buttons he asked for, has never been necessary. In any case, I added another layer to navigate through by adding a pop up screen to make it harder to accidentally push either of the manual buttons.

[Evilbeard]

Glad we got our suspect. I hope the trial is speedy.

[Garyhlucas]

If the HMI supports it put time delays on all buttons you don’t want pushed by accident. Just did this on a C-more at a job and it works well.

[Controls Guy]

Well, the HMI will by definition support it.  Link the button to a PLC coil, then time it yourself before doing the action.  HMI couldn't stop you if it wanted to.

[BobO]

DEBOUNCE instruction.

[Garyhlucas]

DEBOUNCE instruction.

Well DUH!