173 lines
7.5 KiB
HTML
173 lines
7.5 KiB
HTML
<html>
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<head>
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<title> Histogram memory</title>
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</head>
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<body>
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<h1>Histogram memory</h1>
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<hr size=4 width="66%">
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<p>
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Histogram memories are used in order to control large area sensitive
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detectors or single detectors with time binning information.
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Basically each detector maps to a defined memory location. The
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histogram memory wizard takes care of putting counts detected in the
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detector into the proper bin in memory. Some instruments resolve energy
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(neutron flight time) as
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well, than there is for each detector a row of memory locations mapping to
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the time bins. As usual in SICS the syntax is the name of the histogram
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memory followed by qualifiers and parameters. As a placeholder for the
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histogram memories name in your system, HM will be used in the following
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text.
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</p>
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<p>
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A word or two has to be lost about the SICS handling of preset values for
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histogram memories.
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Two modes of operation have to be distinguished: counting until a timer has passed,
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for example: count for 20 seconds. This mode is called timer mode. In the other
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mode, counting is continued until a control monitor has reached a certain
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preset value. This mode is called Monitor mode. The preset values in Monitor
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mode are usually very large. Therefore the counter has an exponent data variable.
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Values given as preset are effectively 10 to the power of this exponent. For
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instance if the preset is 25 and the exponent is 6, then counting will be
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continued until the monitor has reached 25 million. Note, that this scheme with
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the exponent is only in operation in Monitor mode.
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</p>
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<h2>Configuration</h2>
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<p>
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A HM has a plethora of configuration options coming with it which define
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memory layout, modes of operation, handling of bin overflow and the like.
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Additionally there are HM model specific parameters which are needed
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internally in
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order to communicate with the HM. In
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most cases the HM will already have been configured at SICS server startup
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time. However, there are occasion where these configuartion option need to
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enquired or modified at run time. The command to enquire the current value
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of a configuration option is: <b>HM configure option</b>, the command to set it is:
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<b> HM configure option newvalue</b>. A list of common configuration options and their
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meaning is given below:
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<DL>
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<DT> HistMode
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<DD> HistMode describes the modes of operation of the histogram memory.
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Possible values are:
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<UL>
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<LI>Transparent, Counter data will be written as is to memory. For debugging
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purposes only.
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<LI> Normal, neutrons detected at a given detector will be added to the
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apropriate memory bin.
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<LI> TOF, time of flight mode, neutrons found in a given detector will be
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put added to a memory location determined by the detector and the time
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stamp.
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<LI> Stroboscopic mode. This mode serves to analyse changes in a sample due
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to an varying external force, such as a magnetic field, mechanical stress
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or the like. Neutrons will be stored in memory according to detector
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position and phase of the external force.
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</UL>
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<DT> OverFlowMode
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<DD> This parameter determines how bin overflow is handled. This happend
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when more neutrons get detected for a particular memory location then are
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allowed for the number type of the histogram memory bin. Possible values
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are:
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<UL>
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<LI>Ignore. Overflow will be ignored, the memory location will wrap around
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and start at 0 again.
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<LI>Ceil. The memory location will be kept at the highest posssible value
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for its number type.
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<LI>Count. As Ceil, but a list of overflowed bins will be maintained.
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</UL>
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<DT> Rank
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<DD> Rank defines the number of dimensions the detector has, minus the time channle when applicable. 1 is a linear detector, 2 a area detector etc.
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<DT> BinWidth
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<DD> determines the size of a single bin in histogram memory in bytes.
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<DT>dim0, dim1, dim2, ... dimn
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<DD>define the logical dimensions of the histogram.
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<dt>extrachan
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<dd>Extra time channels as used at AMOR and SANS for time-of-flight
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monitors. They get appended to the main hm data but are treated separately.
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</DL>
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</p>
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<p>
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In addition to these common options there exist additional options for
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the EMBL position sensitive detectors (PSD) installed at TRICS and
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AMOR. These PSDs can be operated at different pixel resolutions. The
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position of a neutron event on these detectors is encoded in a delay
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time value which is digitized into a range between 0 to 4096. This
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resolution exceeds the resolution available from instrument physics by
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far. Useful resolutions are obtained by dividing this raw range by a
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factor. In addition, the coordinates of the center of the detector
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have to given as well (usually size/2).This is done through the
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configuration options:
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<dl>
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<dt>xFac
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<DD>x direction division factor
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<dt>yFac
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<dd>y direction division factor
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<dt>xOff
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<dd>Offset of the detector center in x.
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<dt>yOff
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<dd>Offset of the detector center in y.
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</dl>
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Do not forget to change the standard options dim0, dim1 and length as
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well when changing the PSD resolution.
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</p>
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<p>
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For time of flight mode the time binnings can be retrieved and modified with
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the following commands. Note that these commands do not follow the configure
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syntax given above. Please note, that the usage of the commands for
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modifying time bins is restricted to instrument managers.
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<DL>
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<DT>HM timebin
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<DD> Prints the currently active time binning array.
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<DT>HM genbin <i>start step n</i>
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<DD>Generates a new equally spaced time binning array. Number n time bins
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will be generated starting from start with a stepwidth of step (example: HM genbin 10 1 5).
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<DT>HM setbin <i>inum value</i>
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<DD>Sometimes unequally spaced time binnings are needed. These can be
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configured with this command. The time bin iNum is set to the value value.
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<DT>HM clearbin
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<DD>Deletes the currently active time binning information.
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<dt>HM notimebin
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<dd>returns the number of currently configured timebins.
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</DL>
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</p>
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<h2>Histogram Memory Commands</h2>
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<p>
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Besides the configuration commands the HM understands the following
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commands:
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<DL>
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<DT>HM preset <i>[newval]</i>
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<DD> with a new value sets the preset time or monitor for counting. Without a
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value prints the current value.
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<DT>HM exponent <i>[newval]</i>
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<DD> with a new value sets the exponent to use for the preset time
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in Monitor mode. Without a
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value prints the current value.
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<DT>CountMode <i>[mode]</i>
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<DD> with a new values for <i>mode</i> sets the count mode. Possible values are Timer for a fixed counting time and Monitor for a fixed monitor count which has to be reached before counting finishes. Without a value print the currently active value.
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<DT>HM init
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<DD> after giving configuration commands this needs to be called in order to
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transfer the configuration from the host computer to the actual HM.
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<DT>HM count
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<DD> starts counting using the currently active values for CountMode and
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preset. This command does not block, i.e. in order to inhibit further
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commands from the console, you have to give Success afterwards.
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<DT>HM countblock
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<DD> starts counting using the currently active values for CountMode and
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preset. This command does block, i.e. you can give new commands only when
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the counting operation finishes.
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<DT>HM initval <i>val</i>
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<DD> initialises the whole histogram memory to the value val. Ususally 0 in
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order to clear the HM.
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<DT> HM get <i>i iStart iEnd</i>
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<DD> retrieves the histogram number i. A value of -1 for i denotes retrieval
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of the whole HM. iStart and iEnd are optional and
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allow to retrieve a subset of a histogram between iStart and iEnd.
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<DT>HM sum <i>d1min d1max d2min d2max .... dnmin dnmax</i>
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<DD>calculates the sum of an area on the detector. For each dimension a
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minimum and maximum boundary for summing must be given.
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</DL>
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</p>
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</body>
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</html>
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