Hello naifmbo,
I don't know how to do this with a Siemens PLC, but what you can do is counting the minutes. Use one timer which is set for a minute. If the timer is ready add one to a counter and restart the time.
Best regards,
Henry
Are there on this forum users who use hardware from Sigmatek in combination with Lasal and LSE software?
What experience do you have with Lasal and LSE software?
If you didn't make a choice yet you can also go for unitronics. The hardware is cheap and the software is free. All OPLC's have a userinterface.
They have a good helpdesk.