The XMaS beamline is controlled through a Linux workstation (xmas5 running Debian). The user interface is achieved with use of SPEC software that includes several sessions to control the diffractometer in different geometries: FOURC_VER, FOURC_HOR, SIXC and PSIC (pseudo-Six circle). In order to run a session it is necessary to open a terminal window and then simply type the name of the session (in small letters). It is then possible to drive slits and optical elements as well as the diffractometer by using standard SPEC commands. The sessions also allow the definition of an orientation matrix and subsequent reciprocal space scans.
Two other sessions are used to control the optics and other elements of the beamline: MIRROR and SPECSERV. Generally, these sessions are not needed by the users.
The beamline is controlled through four VME crates (d281, d282, d283 and d284) situated in CC1, CC3 and EH1. The crate d281 in CC1 controls all optical elements, including slit-sets s1 to s5. The crate d282 in CC3 controls the diffractometer and all other experimental equipment. The crates employ a diskless VME system and when booted loads all OS9 device servers into RAM through the Ethernet link from the hard disc of the workstation. Device servers are controlled either through SPEC or through other ESRF clients, via the Ethernet.
All hardware is driven through VME cards such as VCT6 for detectors, CC133 for encoders, VPAP for stepper motors, etc. These cards are hard-wired either to the specific hardware item, such as an encoder for the CC133, or to interface electronics such as DPAP current pulse generators for stepper motors or NIM electronics for the detectors.
Both the vacuum control and personal safety (PSS) systems are hard wired, stand-alone systems controlled by PLC's in the CC1 racks. The vacuum control system automatically closes valves in the event of high pressure, from a leak for example, in a given vacuum section in order to isolate that section. The PSS system enables or disables the opening of the front-end shutter, depending on the status of optics hutch PSS interlocks while the station-shutter is similarly regulated by the status of experimental hutch interlocks. The vacuum control system similarly influences the state of the front-end shutter – i.e. if any valve is closed the shutter will not open.
The workstation (xmas5) also runs several GUI applications that communicate with the vacuum and PSS PLC's. The station-shutter can thus be opened and closed by clicking with the mouse the appropriate icon. Valves can be opened or closed and vacuum gauges read in the same manner.