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<HTML>
<HEAD>
<TITLE>The Internal Scan Command</TITLE>
</HEAD>
<BODY>
<H1>The Internal Scan Command</H1>
<P>
Scans are preformed from a variety of commands in SICS. All these commands
are just Tcl--wrappers around an internal scan object implemented in C. This
section describes this internal scan command and how it works. This internal
scan command is installed into the SICS server via the <a href=command.htm>MakeScanCommand
command</a> in the initialisation file. This command install the internal
scan object under a user defined name. For the rest of this document it is
assumed that this name is xxscan.
</P>
The scan object (named here xxscan, but may have another name) understands
the following commands:
<DL>
<DT>xxscan add name start step
<DD>This command adds the variable specified by the argument name to the
list of variables scanned in the next scan. The arguments start and step
define the starting point and the sptep width for the scan on this variable.
<DT>xxscan clear
<DD>clears the list of scan variables. Must be called before each scan with
different parameters.
<DT>xxscan run NP mode preset
<DD>Executes a scan. The arguments are: NP the number of scan points, mode
the counter mode to use (this can be either timer or monitor) and preset
which is the preset value for the counter. Scan data is written to an output
file.
<DT>xxscan silent NP mode preset
<DD>Executes a scan. The arguments are: NP the number of scan points, mode
the counter mode to use (this can be either timer or monitor) and preset
which is the preset value for the counter. The difference to run is, that
this scan does not produce an output file.
<DT>xxscan recover
<DD>Recovers an aborted scan. The scan object writes a file with all data
necessary to continue the scan after each scan point. If for some reason a
scan has been aborted due to user intervention or a system failure, this
scheme allows to continue the scan when everything is alright again. This
works only if the scan has been started with run, not with silent.
<DT>xxscan getfile
<DD>This command retuns the name of the current data file.
<DT>xxscan setchannel n
<DD>Sometimes it is required to scan not the counter but a monitor. This
command sets the channel to collect data from. The argument n is an integer
ID for the channel to use.
<DT>xxscan getcounts
<DD>Retrieves the counst collected during the scan.
<DT>xxscan getvardata n
<DD>This command retrieves the values of a scan variable during the scan
(the x axis). The argument n is the ID of the scan variable to retrieve data
for. ID is 0 for the first scan variable added, 1 for the second etc.
<DT>xxscan interest
<DD>A SICS client can be automatically notified about scan progress. This is
switched on with this command. Three types of messages are sent: A string
NewScan on start of the scan, a string ScanEnd after the scan has finished
and a string scan.Counts = {109292 8377 ...} with the scan values after each
finished scan point.
<DT>xxscan uninterest
<DD> Uninterest switches automatic notification about scan progress off.
<DT>xxscan integrate
<DD> Calculates the integrated intensity of the peak and the variance of teh
intensity for the last scan. Returns either an error, when insufficient scan
data is available or a pair of numbers. Peak integration is performed along
the method described by Grant and Gabe in J. Appl. Cryst. (1978), 11,
114-120.
<DT>xxscan window [newval]
<DD>Peak Integration uses a window in order to determine if it is still in the
peak or in background. This command allows to request the size of this
window (without argument) or set it (with argument giving the new window
size).
<DT>xxscan simscan pos FWHM height
<DD>This is a debugging command. It simulates scan data with a hundred
points between an x axis ranging from 10 to 20. A gauss peak is produced
from the arguments given: pos denotes the position of the peak maximum, FWHM
is the full width at half maximum for the peak and height is its height.
<DT>xxscan command tclcommand
<DD>Sets the tcl command procedure to invoke at each scan point. See below
for the description of user defined scans. Invoked without argument command
returns the name of the current command procedure.
<dt>xxscan configure mode
<dd>Confugures the several possible scan modes for the scan
object. Currently there are two:
<ul>
<li><b>standard</b>, the default mode writing ASCII files.
<li><b>amor</b>, a special mode the reflectometer AMOR which writes
NeXus files.
</ul>
</DL>
</P>
<p>
<h2>User Defined Scans</h2>
In some cases users wish to exert more influence about the scan. Especially
about what gets counted. In order to cater for this a hook was implemented
in the internal scan command. This hook allows to run a tcl procedure at each
scan point. This Tcl procedure is required to return a string containing
up to 11 values for counters and monitors. The first value will be the one
used as counts in the data file. The others will be placed as monitors.
Please note, that only the first three monitors are written to file as of
current. In order to use this facility the following steps are required:
<ol>
<li>Write The Tcl-macro procedure to run. Make sure that is creates proper
output.
<li>Test the Tcl-procedure in SICS.
<li>Install the Tcl-procedure into the scan object with the
xxscan command name syntax.
<li>Make the scan command use the Tcl procedure by setting channel to -10 with
the xxscan setchannel -10 command.
</ol>
A hint: If you need to control the counting operation as well (because you
are not using a counter to count) just run the scan object with a very low
preset and do the counting yourself in your procedure.
</p>
</BODY>
</HTML>