All areas of a beamline at PETRA III need to be searched before the X-ray beam can be turned on (or, more precisely, the safety shutter in front of each area can be opened).  The purpose of the search is to make sure that nobody is inside an experimental area when the X-ray beam is on. For this purpose the interlock system of PETRA III has been developed which implements the following search procedure:

One (and only one) user is supposed to perform this search.

This user has to start the search procedure by placing an activated DACHS card over the DACHS card reader near the “main” door (all other doors and chicanes to this area need to be closed in advance).  This starts a warning message for the area and activates the first search button (a green button near the door lights up) inside the area. After pressing this button, a light barrier (which is installed to prevent anybody else from entering the area) is activated.

The user proceeds by searching the hutch and doing so pressing all necessary search buttons (green buttons).  After the user is finished with the search he returns to the hutch door and presses the yellow button near the door to deactivate the light barrier for 5 seconds. 

Only then the user is able to leave the area and to close the door.  If the user has succeeded to follow this procedure an orange light will come up near the door.  The search is finished by pressing the last green button outside of the area followed by placing the DACHS card over the DACHS card terminal again.  An additional red light will show up on top of the orange light. 

The warning message will continue for 30 seconds before the safety interlock shutter can be finally opened.