Setting a "daylight savings" bit in Do-More PLC

Finishing up my first project with a Do-More PLC to install tomorrow morning. I'm working on small details.... like automatically adjusting for daylight savings time. I'm thinking the problem through and wondering why nothing comes up in a search. It seems like this would have been encountered several times. Anyway.... I'm thinking about setting up a comparitor to trigger a bit.

Greater than: Second Sunday in March, 2:00, And lesser than: First Sunday in November..... set a bit.

Any nifty ways of doing this? Second Sunday in March.... all I can think of is $Now.day > 7. I'm curious if someone has a method I haven't thought of.

Nevermind, I figured it out.

The trick is to do it so the PLC knows whether or not it's in DST, even if it has been powered down during the change.

It boils down to one week in March, and one in November. Every other time is known, so you can easily do a greater-than or less-than for all the other months of the year, and the other weeks in March and November.

What you're left with is 7 comparison rungs for the unknown days for March 8-13th, and 7 for November 1-6. You utilize the $Now.DayOfWeek in those two weeks' comparisons, since they will only cycle through once.

Did you have an issue with the two-rung example on the AD website?

https://support.automationdirect.com/examples/DM/EP-MISC-028_DM.zip

EDIT:Add link to project

Yes, I do have an issue. I wanted more than a bit set and reset. If the machine is off during the time shift, it gets screwed up. I put a little thought into it last night and wrote a little ladder program that will adjust to DST, regardless of when it is powered-up.

AutomationTechBrian said:

Yes, I do have an issue. I wanted more than a bit set and reset. If the machine is off during the time shift, it gets screwed up. I put a little thought into it last night and wrote a little ladder program that will adjust to DST, regardless of when it is powered-up.

Click to expand...

There is also an example program to do that. It is the first example on the page. However, it is targeted at DL-series cpus.

http://accautomation.ca/adjusting-daylight-savings-time-in-do-more/

Glad you got it working.