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