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Notes on the IRPOL EPICS control panel
(May 2002)

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The EPIC screen shown above can be used to control IRPOL (although observers should always use the irpol iterator in the ORAC-OT when conducting a polarimetry run). Below we describe briefly the functionality of the epics screen.

• The IRPOL waveplate can be moved to one of six angles using the six "Demand Position" buttons provided. Alternatively, the waveplate can be moved to ANY angle by entering a number in the "Demand Angle" field.
• "DATUM IRPOL" checks all switches (i.e. it moves to all "named" positions and reads all switches in the process); it should therefore report "Error" if a switch isn't seen, e.g. because the waveplate didn't move.
• In addition to "HP Status" and "Move Status" there is an "Overall Status", which is a combination of the previous two. "Overall Status" will report "Error" when the HP status contains an error, e.g. on startup after a reboot, or when a move to a named position doesn't complete.
• The "Angle After Move", which is the angle that gets stored in each data file header, switches back to 0 after a "Datum" (because that's where "Datum" moves to).

Caveat 1: Moving to particular angles by entering a random number in the "Demand Angle" field (rather than by clicking on one of the six Angle buttons) will not read any switches.

Caveat 2: Moving "by steps" (currently not possible from the above epics screen) will not change the position on the screen or in the value stored in a data file.

Notes for TSS and/or Support Scientist

The power to the position switches is independent of the power to the motors.

Also, keep in mind that the motor controller (the HP unit in the computer room) should normally be switched off when IRPOL isn't being used, so always check that the power is on before trying to use IRPOL. And in spite of there being provisions for this in the software now, it is always a good idea to make sure that the waveplate really does move to different angles when requested to do so!

Control of the IRPOL arm (i.e. lowering it into the beam) is not part of the above epics window; the waveplate arm must be lowered into the beam manual from ISU2 (by the TSS ONLY).