The PMAS instrument control system is fully under remote control, except for the exchange of gratings and A&G camera filters.  In this section, the most relevant features of the control system are explained.

The instrument control hardware consists basically of three major hardware controllers, and a SPARC workstation ("rike") which provides a command interface to the user. The control software as seen through this interface is graphically shown in Fig. 1. The instrument control software has a 4-layer structure, of which the two upper levels are accessible to the observer. The default user interface is provided through the IDL command line.

Instrument Control Software Structure :

embedded controller software

low level hardware control

user level IDL command line interface

user level graphical user interface (GUI)

For the purpose of rebooting the system in the event of power failure or similar problems, it is useful to understand which hardware devices are forming the PMAS instrument control system (Fig. 2).
Hint: Switch back and forth between Fig. 1 and Fig. 2 to better understand the meaning of logical access and hardware architecture.

Instrument Control Hardware :

Fiber Spectrograph CCD Controller (specACE), often indicated by "s" or "spec"

A&G Camera CCD Controller (agACE), often indicated by "a" or "ag"

VME Hardware Controller (Motors, Lamps, Shutters) running under VxWorks ("lea")

Data Acquisition and Master Control SPARC Workstation ("rike")

Terminalserver

EPICS Database :

The EPICS database is an important feature of the instrument control system: all relevant physical parameters of the instrument are reflected in real-time in this database, which resides in lea (VME Controller). Consequently, lea must be online for any function of the instrument, even if not directly controlled from lea. This is in particular true for any of the two ACE systems (CCD controllers). EPICS database entries can be accessed for special purposes from IDL. During normal operation, the database is transparent to the ordinary user.

 Note:
The PMAS Status Window, which is created by typing "dm2k" on the unix prompt of rike, is connected directly to the EPICS database and updated with important instrumental parameters in real time. Consult this window to check focus settings, the grating angle, A&G Camera filter positions, lamps, shutters, and whether or not the calibration unit or the A&G stage have reached their active / parking positions.
 

Telescope Control :

The telescope control system is connected to the PMAS instrument control system through scripts, allowing for read operations of telescope parameters, for changing the telescope M2 focus setting, slewing the telescope, and guiding. Note that within the PICS environment any write command attempting to access the telescope is blocked unless specifically released (pics_logon procedure). This feature is especially important when PMAS is operated in standby mode in the storage room.
 

Hardware Failure :

In the event of a device failure, it may be possible to continue operation if the malfunctioning part (e.g. motor) has stopped in an tolerable position. The device can be logically switched off from a setup-table, thus leaving the rest of the control software intact. In this case, the grating,  the fiber spectrograph focus mechanisms and the linear stages of the Calibration Unit / A&G Camera Pickoff-Mirror may also be moved mechanically to a safe position.