Timing adjustment of the pressure ON

Hi, i have Rapida 74 and have issue with timing of engaging blanket cylinder to plate and sheets.
Can some one tell how to change this adjustments? Is there any sensor for this?
This cause issue that first sheet has half of the job the next few sheets has hal tones of the ink, then 5 or 6 sheet is ok...


thanks a lot and regards

 

The machine has an encoder for all angle related functions.

 

thanks McGuyver...
This I know... But how it is possible that PLC of each printing tower wrongly count revolution means wrongly detected position of paper sheet which resulting half sheet printing on the first sheet...
How I can change this? Do you have any parameter list of the PLC which could be changed...