[Nexus] How to model a grating monochromator?

[Pete Jemian]

Gerd:

Discussion was resolved today on NXpositioner.  Additional fields need 
to be added to document common parameters and various types of 
positioners (stepper motors, servo motors, piezo-electric transducers, 
inch-worm motions, ...).  Usage is intended to be one or more subgroups 
of NXcollection like this:
   beamline has "n" motors
   create an NXcollection group with name of (for example) "positioners"
   create "n" NXpositioner groups inside "positioners:NXcollection"
   store positioner data

Now, when considering other base classes that might also use the same 
positioner information, make a link to the particular positioner as 
appropriate.

Consider a hypothetical SAXS camera for an example, the sample-detector 
distance might come directly from the value of positioner "az":
/NXsas/NXinstrument/NXdetector/distance
      --> positioners:NXcollection/az:NXpositioner/value


As for NXgrating, I will seek experts for content suggestions.  Please, 
forward your suggestions.  I'll add them to the TRAC ticket.

	http://trac.nexusformat.org/definitions/ticket/158

Pete


On 12/1/2010 3:11 AM, Wellenreuther, Gerd wrote:
> Hi Pete,
>
> thanks for answering!
>
> About the grating: I can ask Jens Viefhaus, who will be using gratings
> for his beamline at PETRA III, to help me compiling a list of parameters
> required to describe a grating used in monochromators. Or maybe there is
> some expert from Bessy / HZB who could do this as well or better?
>
> About the motors/NXpositioner: I think we definitely need a defined way
> of saving not only the position of a motor, but all its settings ( think
> of soft- and hard-limits, slew_rate, acceleration, stepping_mode,
> currents, home, conversion, encoders & calibration, units, ...) . This
> should be handled by a base class, IMHO.
>
> What is not clear to me yet is given a device like a crystal in a
> monochromator, and given a couple of devices like motors moving/tilting
> such a crystal - how should I define what a certain motor is actually
> doing? Just trying to deduce the motors function from a name sounds
> dangerous ...
>
> Cheers, Gerd
>