RS Logix500 - Astronomical clock

nasps

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Join Date
Sep 2007
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Aveiro
Posts
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Hello everybody! Here's an odd request. I need to make an astronomical clock to control an outside ilumination but I don't want to have to every month to change the on and off set-points. The best thing is to have an astronomical clock where I can set at once all the setpoint for every month. Does anybody have an algorithm for this clock?
Thanks in advance
 
Just out of curiosity why couldn't you just add a light sensor to the outside of the building?

Lights come on at dusk and turn off at dawn
 
nasps said:
...The best thing is to have an astronomical clock where I can set at once all the setpoint for every month.
Click to expand...

If it were I... and keep in mind I don't know your details on your application, but why don't you go with a photocell that give you a input, then when it get dark or light it switches, then if you have a massive thunder storm roll in, you lights will turn on :)

If I am understanding you question correct...

EDIT... typing to damn slow (Hi Tim :) )
 
Hi. Thanks for your contribution. The use of a photocell was the first thing to do but we are talking (I haven't refered) about 60 instalations to control the lights, all of them with PLC's AB. That's why, in a effort to not spend much money, the possibility to use the PLC to do that control. Actually I'm using a simple routine with LIM to control but as we get closer to the Winter Solstice the days are getting smaller and I need to re-programm the set-points. That's why I'm trying to figure out another way.
 
A simple algorithm would be to have the program adjust the turn-on and turn-off times by some increment each day. The increment would would vary according to the date. Near the solstices, the increment is smallest. Near the equinoxes, the increment is largest. You could include a correction to set the turn-on and turn-off times to some specific time at the solstices and equinoxes so that any error in the size of the increment is not cumulative.
 
nasps said:
They are all in a network!
Click to expand...
Are they all at pretty much the same physical spot?

Steve's algorithm may be doable or one photocell and messaging between the PLCs. Of course 60 messages would have to be staggered because of connection limitations. What PLC are you using?
 
Unfortunelly they are not in the same location! The longest distance between two is 80 km.
I'm using SLC500 and SIEMENS S7-300
 
80km is probably close enough for Steve's method, but at that distance I'm guessing that your going over the internet to connect them, not a good idea for the single photocell idea.

I guess the question is how much time vs money do you want to spend? You can buy a light sensor for about $5-$10. So your looking at $300 to $600 to install sensors on each one.
 
TWControls said:
80km is probably close enough for Steve's method, but at that distance I'm guessing that your going over the internet to connect them, not a good idea for the single photocell idea.

I guess the question is how much time vs money do you want to spend? You can buy a light sensor for about $5-$10. So your looking at $300 to $600 to install sensors on each one.
Click to expand...

DITTO....

How's that for typing skills :D
 
More detail on my thinking.

Starting at a solstice, set the turn-on and turn-off times to some fixed time. For the next three weeks, adjust the turn-on and turn-off times dialy by a minimum increment. For the next four weeks after that, adjust the times by a larger daily increment. For the next six weeks after that, adjust the times by a maximum daily increment. That brings you to the equinox where you set the times to a specific value. Following the equinox you adjust in reverse order as when proceeding from solstice to equinox, which brings you back to the next solstice where you correct to specific turn-on and turn-off times.

Repeat for the other half of the year.

Correction for longitude would be the specific times to use at the eqinoxes and solstices. Correction for latitude would be the size of the daily incremental adjustments.
 

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