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<HTML>
<HEAD>
<TITLE>Four Circle Diffractometer Measurements in Single Counter Mode</TITLE>
</HEAD>
<BODY>
<H1>Reflection List Processor</H1>
<P>
This section describes the means for doing a standard single counter four
circle diffractometer measurement with SICS. A prerequisite for that is a
file with a list of reflections to measure. This is a simple file with
three floating point values per line giving the HKL of the reflection to
measure. Do not forget to put standard reflections into that file any now
and then. Another prerequisite is, that the UB-matrix had been determined
beforehand and that SICS has the updated values. Also check the value of
lambda in the hkl-object.
</P>
<p>
The measurement procedure is rather simple: If a reflection is accessible
the diffractometer is positioned on that reflection. Then a scan is done for
the reflection and data written to file. The scans all run with a fixed scan
widths, counter preset and countmode. There is a choice of omega scan or
omega two theta scan. It is known that there are more sophisticated
measurement schemes for four circle diffraction, but as TRICS is only
temporarily operated with a single counter not much optimisation seemed
necessary.
</p>
<p>
Three files will be written starting from a root such as tricsnumberyear.
For instance trics05601998 means file number 560 in 1998. The file ending in
.log will contain the console log. This is extremely verbose. Another file
ending with .col will contain the reflection, diffractometer settings and
the measured profile. The third file, ending with .rfl will contain for each
refelction, the HKL, the diffractometer settings and the intensity and sigma
intensity as calculated by the SICS internal integration routine. It does
a Grant Gabe integration (see J.Appl. Cryst (1978), 11, 114-120).
</p>
<p>
For the purpose of the command description it is assumed, that this facility
is accessible as object mess within SICS.
Interaction with this object happens through the following commands:
<dl>
<DT>mess start
<DD>Creates a new set of files and writes some header info.
<DT>mess measure filename iSkip
<DD>Starts a measurement. Reads reflections from the file filename. iSkip is
an optional parameter which allows to skip iSkip lines in the file. This
is for recovery in cases of accidental or purposeful interruption
of the measurement.
<DT>mess genlist filename iSkip
<DD>Mesures reflection from filename. The file is expected to have been
created by hklgen and to include all the angle settings. The optional
parameter iSkip determines the number of lines to skip in the file. This
feature allows to continue measurement on not fully processed files.
<DT>mess reopen filename
<DD>Reopens an already existing file set for appending. Only the file root
without directory info or endings needs to be given.
<DT>mess close
<DD>Closes the current data file set.
<DT>mess file
<DD>Prints the current data file name.
</dl>
Then there are a few parameter commands. They follow the general scheme:
<dl>
<DT>mess parameter
<DD>Prints the current value of the parameter
<DT>mess parameter value
<DD>Sets the parameter to the new value.
</dl>
This object knows about the following parameters:
<dl>
<DT>countmode
<DD>The counting mode to use. Possible values are timer or monitor.
<DT>preset
<DD>The preset to use for counting
<DT>mode
<DD>The measurement mode. Posssible values are omega for omega scans and
omega2theta for omega two theta scans.
<DT>np
<DD>number of points to collect for each profile.
<DT>step
<DD>The step width in omega to use for scanning.
<DT>compact
<DD>Determines if the scan data output to the SICS is in normal
(compact = 0) or condensed (compact = 1) form. The default is 1.
</dl>
</p>
<p>
mess supports two geometries: the first is the usual bisecting geometry. The
second is the normal beam geometry where the detector is moved out of plane.
This si accounted for by two switches:
<dl>
<dt>mess bi
<dd>switches into bissectiong mode. This is the default.
<dt>mess nb
<dd>switches into normal beam mode.
</dl>
</p>
<p>
This object supports some file management functionality. It caters
for the problem that experiments may need to be continued. Thus reopening
files and continuation of reflection processing at a point way down the
reflection file is supported. Consequently the start of a new experiment
requires the following steps:
<ul>
<li>Create a new set of files with <b>mess start</b>.
<li>Configure the scans with the parameter commands.
<li>Start processing a reflection file with either the <b>mess genlist</b>
or <b>mess measure</b> commands.
</ul>
If you need to continue reflection file processing after an abort or after
solving a problem the following steps are required:
<ul>
<li>Determine the file number you were working at and the line number in the
reflection file where you wish to continue processing.
<li>Set the file root with the <b>mess reopen</b> command.
<li>Configure the scan parameters again.
<li>Restart the measurement with either <b> mess genlist</b> or <b> mess
measure</b> but specify the iSkip parameter according to the position in
the reflection file where processing should continue.
</ul>
</p>
</BODY>
</HTML>