day light savings time

i was looking for help on programing daylight savings time on allen bradley slc500

Since the SLC's which have real-time clock information do not have 'day of week' this becomes a bit fun. You can start a register with a number (0-6) and adjust it each night at midnight.


After that you must check for the proper month, day range and day of week so that you can do the adjustment. For the fall adjustment don't forget to make a bit saying that you've already adjusted it or you'll keep doing it over and over.

a quick search yielded this...
http://www.plctalk.net/qanda/showthread.php?t=9123&highlight=day+light+savings+time

I did that in an SLC500 here, but it's not too cute. We have a couple processes that need to start up 1/2-1 hour prior to the start of each shift.

What I did was to compare the date and time and in the spring, add one hour, fall subtract one hour. I did this so that I did not have to hook up my laptop twice a year just to move that one hour.

Problem with my set up, is that every year, it does that same date, even though daylight savings is on a different date each year. The guys compenate for the days that it's off, by making sure someone has the precesses started manually for those few days where I'm off sync. I used to adjust to actual dates when ever I was in the PLC, but it was easier to just remember the same dates each year.
I'm sure there's a better way, but 4-5 years ago, that was all I came up with. (Haven't thought about it in just about that long, either, so I'll be watching this one.)

Someday PLC's will have this built-in, like PCs do... until then, maybe it can be done like humans do it...

You could have a simple one button routine that will do the "Spring-Ahead" thing (add one-hour to the current time, as in spring-ahead). And another button that will do the "Fall-Back" thing (subtract one-hour from the current time). Of course, just as we regular folk need a reminder that the daylight savings adjustment occurs today... you need to have a means to notify the production folk that an adjustment is necessary... really soon.

The notice, should, or could, be in the form of a memorandum, e-mail, whatever, indicating... Don't Forget! Day-Light Savings adjustment today, or tonight.

Of course, this can be a bi#ch for those processes that generate reports based on time... if the production folks forget... then... grief.

As for many PLC decisions... it's a trade-off.

You can download one way of doing it HERE

The SLC500 does have day of the week register

S:53 Reserved/Clock Calendar Day of the Week

This makes determining the first sunday of the month alot easier