RSLogix and Timer question

waskojat · Aug 3, 2005

I am trying to develop a system where I can control all the HVAC fans using the exsisting PLCs. I am new to programming with RSLogix. The program I want to create would have to know the day and time so it can adjust the HVAC units accordingly - like turning them off at 5pm and turning them on at 6am on weekdays and then shutting off for the weekend. I am just trying to find a starting point and was looking for some answers!

let me know if you can help!

Thanks
Jim

LJBMatt · Aug 3, 2005

All the AB PLC's have internal time clocks that you can use for Date and Time functions and not have to rely on counters. Check the help file for what type of Logix you are using (5,500,5000) to find out how to access this.
Nice to see someone else is from Dayton, OH too.

OkiePC · Aug 3, 2005

In a SLC or PLC5, keeping track of the day of the week will require some minimal extra programming. There was a recent discussion about daylight savings time that touched on this.

waskojat · Aug 4, 2005

progress

I am using the GSV - wallclocktime DINT[7] in RSLogix 5000. I am taking each value and moving it to its own tag for year, month, etc. should those tags also be DINT? what else do i have to do to ensure the time is correct on the PLC?

waskojat · Aug 4, 2005

Weekends

Is there a way I can account for a weekend with Wallclocktime ?

bioplc · Aug 4, 2005

You can move any values to the clock calendar of 5/60 processor using MOV instruction.
S:20 = Month
S:19 = Day
S:18 = Year

i hope this answers your question.

Oakley · Aug 4, 2005

I once did something like this via a recipe in the HMI.

Another instance was somewhat sophisticated due to the Facilities Manager scheme. We had installed a switch on each of the production lines, mapped them to what lighting zone(s) they occupied, and controlled the plant lighting. The next step was to control the AHU dependent upon the same concept - we chose to use the lighting status because the production lines were constantly shrinking/expanding.

Just two of the possibilities I have come across in the past.

russrmartin · Aug 5, 2005

I had to do something like this as well, only it was imperitive that the time be correct at all times. The one thing to watch out for is program downloads. Each time the new program is loaded, you may have to adjust the data for the wall clock time again. Just something to look out for.

LJBMatt · Aug 5, 2005

A cheap way to do this is when the day changes in your WallClockTime to increment a counter and (as an example) have monday thru friday be values 0-4. Then weekends will be values 5-6. When the counter changes to 7 reset the counter because you know you are back on Monday.

RSLogix and Timer question

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