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PSI sics-cvs-psi_pre-ansto

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koennecke
2003-06-13 00:00:00 +00:00
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<html>
<head>
<title>The Scan Command </title>
</head>
<body>
<h1>The Scan Command </h1>
<hr size=4 width="66%">
<p>
An important concept in neutron scattering instrument control is a
"scan". For a simple scan a range of instrument positions is divided
into equidistant steps. The instrument then proceeds to drive to each
of these points and collects data at each of them.
</p>
<p>
The general idea of the scan object is, that you configure the
scan by typing commands at the command line. Once, the configuration is
finished the requested scan is started. A data file will be written
automatically to the default location. The scan command can not only scan
over motors but also about some variables which relate to motors. For
instance lamda for the wavelength. Scan can scan over more then one variable.
The syntax of the scan command in some detail:
<DL>
<DT>scan clear
<DD> Clears current scan parameters.
<DT>scan list
<DD> lists current scan parameters.
<DT> scan var <i>name start step</i>
<DD> Defines a parameter (motor) to be scanned. The name of the parameter, a
start value and a step width need to be given. More then one scan variable
can be specified.
<DT> scan modvar <i>name start step</i>
<DD> Modifies the scan parameters for scan variable name to the new values
given.
<DT>scan getvars
<DD> Returns a list of currently active scan variables terminated with the
string -END-.
<DT> scan np <i>num</i>
<DD> Sets the number of scan points.
<DT> scan preset <i>[val]</i>
<DD> Sets the Preset value for the scan. Without a parameter, inquires the
current value.
<DT> scan mode <i>[val]</i>
<DD> Sets the count mode for the scan. Without a parameter, inquires the
current value. Possible values are <i>timer</i> or <i>monitor</i>.
<DT> scan run
<DD> Executes the scan.
<DT>scan cinterest
<DD> This call enables automatic printing of scan counts to your connection
when new values arise. This command is primariliy of interest for status display
clients.
<DT>scan pinterest
<DD> This function makes the scan command send a notification (the string
ScanVarChange) to you whenever the scan variables get modified. This command
is primarily of interest for status display clients.
</DL>
</p>
<h2>Center Scan </h2>
<p>
Center scan is a convenience command which starts a scan around a specified
center value. This mostly used for centering purposes. The syntax is like this:<BLOCKQUOTE>
<b>cscan</b> <i>var center delta np preset</i>
</BLOCKQUOTE>
All parameters must be specified. The parameters and their meanings:
<UL>
<LI><b>var</b> is the variable which is to be center scanned.
Only one can be specified.
<LI><b>center</b> is the value to use as center of the scan.
<LI><b>delta</b> is the step width to use for the scan.
<LI><b>np</b> is the number of points to scan in each direction.
<LI><b>preset</b> is the preset to use for the counter. As the counter mode,
the mode currently configured active in the scan object is used.
</UL>
<BLOCKQUOTE>
example: <b>cscan</b> <i>d2hr 0.5 0.01 10 10000</i>
</BLOCKQUOTE>
</p>
<h2>Simple Scan </h2>
<p>
Simple scan is a convenience command which starts a scan for one to several
variables with a simplified syntax. The syntax is like this:
<BLOCKQUOTE>
sscan <i>var1 start end var2 start end ... np preset</i>
</BLOCKQUOTE>
All parameters must be specified. The parameters and their meanings:
<UL>
<LI><b>var1 start end</b> This is how the variables to scan are specified. For
each variable scanned the name of the
variable, the start value and the end value of the scan must be
given. More then one triplet
can be given in order to allow for several scan variables.
<LI><b>np</b> is the number of points to scan.
<LI><b>preset</b> is the preset to use for the counter. As the counter mode,
the mode currently configured active in the scan object is used.
</UL>
</p>
<h2>Peak And Center</h2>
<p>
These two commands are related to the scan command insofar as they act upon
the results of the last scan still in memory. The command <b>peak</b> prints
the position, FWHM and maximum value of the peak in the last scan. The
command <b>center</b> drives the first scan variable to the peak center of the
last scan. Both peak and center use a rather simple but effective method for
locating peaks. The prerequisite is that the peak is approximatly
gaussian shaped. The
algorithm first locates the peak maximum. Then it goes to the left and
right of the maximum and tries to find the points of half maximum peak height.
The two points are interpolated from the data and the peak position
calculated as the middle point between the two halfheight points.
</p>
</body>
</html>