UB matrix stuff
I assume the UB-stuff is with the intention that one can eventually
drive out of the AB-plane using the goniometers? For some experiments -
e.g. the incommensurate stuff Oksana, Sabine and I are working on, this
would be extremely useful.
This is implemented with the Q3 variable. The only difference to the QH
variable is, that it does really move out of the scattering plane, whereas
a drive on QH gives an error when a vector outside the scattering plane
is given. What remains open, is, how to resolve the redundancy on
drives outside the scattering plane. For EN=0, you have 4 angles to drive,
but only 3 components of the Q vector. We have to specify, how to resolve
this redunant information. One possibility would be, that the vector
in the AB-plane, which is perpendicular to the scattering vector, stays
in the scattering plane.
One solution to redundancy problem would be to choose solution that has minimum total tilt - sqrt(Gu^2+Gl^2) would do.
Crystal Orientation Tool
Related to this is a command to tilt the current scattering vector.
Normally we always rotate the sample or the cryostat to have the
crystallographic axes along the goniometer axes. But this is silly since
instead of scanning sgu and sgl independently one can just make a
coupled scan that exactly tilts the current scattering vector. Much of
the time, this is a small convenience thing, but sometimes, the sample
does not have refelctions at perpendicular angles, in which case such a
feature would allow more accurate alignment.
Me also, I thought about a virtual motor simulating a goniometer with
arbitrary axis. I think about a syntax to implement this.
Special Stuff of individual Instruments
The other thing we need to think about is how to deal with the
multiplexing. For RITA-II its only 7-9 channels, but for EIGER-CAMERA it
will be 60 degree continuous scattering and 5 of those. We obviously do
not need to sort that out in detail before when CAMREA is closer to
ready, but we should make sure that the syntax and underlying code can
be generalised to this kind of analyser-detector systems.
I did not specify such things. The aim is, to have the same syntax
for all stuff common on the 3 instruments. I have also not specified
in detail the polarisation analysis, which is only used on TASP.
But if something is found in the syntax, which might give
trouble when extended to some instrument specific stuff, then we like
to have a feedback.
thanks Christoph to have sent me the link.
The following is just the result of some suggestions
that I can think of after discussion with Christof and Markus.
Sorry if they are redudant.
-It is written that En is set to zero in case
the command 'Sc Qh h k l' does not contain the energy transfer. I think
this is quite dangerous if somebody forgets to do it and the instrument
drives back automatically to the elastic position.
-It seems there will be no switches in future apparently. Please remember that
TASP has polarisation analysis.
-The option with the UB matrix allows scans out of the scattering plane.
Some security should be installed to prevent that a typo in a scan or in
a job drives the goniometers (and the cryostat that is on it). I am not sure
that setting the soft limits is a good option. I like Markus' proposition with
the 'sc/dr Q3' command very much.
This page last changed on 10-Mar-2006 10:50:33 CET by Roessli.