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I have a number of lights that will be connected through relays to the DOs of a PLC. The lights must automatically turn on one hour before the sunrise and switch off one hour after the sunset. Is this usually something that is a built-in function at the PLC software interface? If yes, what brands of products support this? If not, what would you suggest? Thank you in advance. My email is e.linou @ yahoo. com

If this is a student project, then this isn't something that PLCs inherently do. You will have to write a program that calculates the appropriate times and compares them to the current time to decide when to turn the lights on or off.

If this is a real-life project, then you probably don't want to use a PLC for this application. There are time of day timers which exist for this specific application and which would be much cheaper and easier to use. I can't recommend one in particular, but a large electrical hardware distributor should have several different models you can choose from.

Hi,

If your PLC has web access then why not use the information from one of the weather sites. I do this with great success, by extracting forecasted temperatures. There is no reason why you should not extract sunrise and sunset times.

Practically though, sunrise and sunset times have little to do with light levels (especially on my grey little island!) and if the lighting is safety related, then some type of lux sensor would be better.

Marc Sinclair

http://s7-200.germainesystems.eu

Hi Marc,

Thank you very much for the "enlighting" idea. I will search this a bit more since I am new on this and don't know how it can be implemented, but I think my PLC will have web access. I hope I can bother you again with this issue if necessary.

Elinou