Date Time comparison in RSLogix 500

nasps · Sep 4, 2007

Hi everybody!

I'm trying to make an external lightening system time-controlable with AB SLC 5/05.
I'm with some dificulty in compare specific time (hours:minute) because I want that an output stays ON between 19:00 and 07:00(next day). The other remaining period, the exit is off!

Any help?

Thanks in advance.

Ken Moore · Sep 4, 2007

This quick example should get you started:

nasps · Sep 4, 2007

Hi Ken! Thanks very much for your tip. The quick example is very useful. I'm having a little trouble with minutes. For example: Lights On > 19:15
Lights Off > 07:30.
The bit must always be ON for the time that it suposed to be ON and OFF for the remaining period. Imagine that the CPU fails in an ON time and returns to normal state in an OFF time, the lights must "go down"!
In situations that the desired time is xx:00 no problem, but I must see all possibilities.

Thanks for any suggestion!

Oakley · Sep 4, 2007

How about using a LIM?

nasps · Sep 4, 2007

Hello Oakley! One of the problems is that the timestamp is divided in 3 status word hh:mm:ss and its not easy to compare 2 diferent words (hh:mm)when the slightest change in the conditions creates problems in the output.

firebrd10 · Sep 4, 2007

The easy way

I honestly hate using latching instructions but, this is a great place for them.

Try the following logic...
HH = 19 and MM = 15 OTL
HH = 7 and MM = 30 OTU

The downfall of the above logic is that it only sends the lights on command at 19:15 and the lights off command at 7:30. This means if the lights are off and you start your logic at 20:00, the lights will not come on till the next day when the clock hits 19:15.
If this is an issue, you will need to go back to your greater then and less then comparisons.

Good Luck,
Tim

nasps · Sep 4, 2007

That's what I'm trying to work around!

Thanks for the tip!

Mickey · Sep 4, 2007

Combine hours and minutes into one word. Then do as Oakley subjested.

nasps · Sep 4, 2007

Done it! Thank you all!

Oakley · Sep 4, 2007

Because you want the output to be ON between 19:00 and 07:00, for this to work correctly you will want the Low Lim = 1900 and the High Lim = 0700.

By reversing the limits, it effect says that if you are outside the limits, then turn on the output.

Date Time comparison in RSLogix 500

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