Add value based on time?

[Iogo]

Is it possible, and how, to add a value to a variable after a certain time perioid passes?

For example I would like to add a value to variable, after each second.

This is for counting kj/s and after a 24h perioid passes convert kj/s to kwh and add this to another variable. This is for energy measurement

[TomasKnot]

You can do this easily with a simple function block, specifically Integer Scheduler (T19), or Bool Scheduler (T17). Signal from these can be used to trigger a function block which sums the value from a counter to some stored value, and the nulls the counter afterwards.

I recommend looking through some online tutorials on function block diagrams (FBDs) and structured text (ST), as well as thoroughly reading the "help" topics in the IDE (press F1).