base class, extends NXobject
A device blocking the beam in a temporal periodic pattern.
A disk which blocks the beam but has one or more slits to periodically let neutrons through as the disk rotates. Often used in pairs, one NXdisk_chopper should be defined for each disk.
The rotation of the disk is commonly monitored by recording a timestamp for each full rotation of disk, by having a sensor in the stationary disk housing sensing when it is aligned with a feature (such as a magnet) on the disk. We refer to this below as the “top-dead-center signal”.
Angles and positive rotation speeds are measured in an anticlockwise direction when facing away from the source.
This symbol will be used below to coordinate datasets with the same shape.
n: Number of slits in the disk
- Groups cited:
@default: (optional) NX_CHAR
Declares which child group contains a path leading to a NXdata group.
It is recommended (as of NIAC2014) to use this attribute to help define the path to the default dataset to be plotted. See https://www.nexusformat.org/2014_How_to_find_default_data.html for a summary of the discussion.
type: (optional) NX_CHAR
Type of the disk-chopper: only one from the enumerated list (match text exactly)
Any of these values:
Chopper type single
Chopper rotation speed. Positive for anticlockwise rotation when facing away from the source, negative otherwise.
slits: (optional) NX_INT
Number of slits
Disk spacing in direction of beam
Angle of each edge of every slit from the position of the top-dead-center timestamp sensor, anticlockwise when facing away from the source. The first edge must be the opening edge of a slit, thus the last edge may have an angle greater than 360 degrees.
Timestamps of the top-dead-center signal. The times are relative to the “start” attribute and in the units specified in the “units” attribute. Please note that absolute timestamps under unix are relative to
@start: (optional) NX_DATE_TIME
Angular separation of the center of the beam and the top-dead-center timestamp sensor, anticlockwise when facing away from the source.
Radius of the disk
Total slit height
Chopper phase angle
Time difference between timing system t0 and chopper driving clock signal
ratio: (optional) NX_INT
Pulse reduction factor of this chopper in relation to other choppers/fastest pulse in the instrument
Effective distance to the origin
Low and high values of wavelength range transmitted
GEOMETRY: (optional) NXgeometry
Table of hypertext anchors for all groups, fields, attributes, and links defined in this class.
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