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Rhs chopper #1610

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7499bc9
add additional field
ggoneiESS Jan 8, 2026
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ggoneiESS Jan 8, 2026
2978abf
add additional field
ggoneiESS Jan 8, 2026
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29 changes: 20 additions & 9 deletions base_classes/NXdisk_chopper.nxdl.xml
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Original file line number Diff line number Diff line change
Expand Up @@ -45,9 +45,23 @@
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.
direction when facing away from the source unless otherwise specified in the `handedness` field.
</doc>

<field name="handedness">
<doc>
Direction of measurement for rotation and positions in the disk-chopper.
Left is the default for historical reasons and implies positive rotation and angles in an anticlockwise
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@phyy-nx phyy-nx May 27, 2026

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Suggested change
Left is the default for historical reasons and implies positive rotation and angles in an anticlockwise
Left was assumed in the past and implies positive rotation and angles in an anticlockwise

direciton when facing away from the source.
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direciton when facing away from the source.
direction when facing away from the source.

Right matches the default NeXus coordinate system and implies positive rotation and angles in an anticlockwise
direction when looking towards the source - positive rotation matches the positive roll of the system.
Only one from the enumerated list (match text exactly).
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Only one from the enumerated list (match text exactly).
Only one from the enumerated list (match text exactly). If `handness` is not specified, it's likely that downstream consuming applications will assume left-handed.

</doc>
<enumeration>
<item value="Left" />
<item value="Right" />
</enumeration>
</field>
<field name="type">
<doc>Type of the disk-chopper: only one from the enumerated list (match text exactly)</doc>
<enumeration>
Expand All @@ -58,8 +72,7 @@
</field>
<field name="rotation_speed" type="NX_FLOAT" units="NX_FREQUENCY">
<doc>
Chopper rotation speed. Positive for anticlockwise rotation when
facing away from the source, negative otherwise.
Chopper rotation speed.
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Chopper rotation speed.
Chopper rotation speed, in the convention of the handedness of the chopper.

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Note, it's a bit odd that the user can specify a negative rotation speed to bypass the handedness. Is that the convention in neutrons?

</doc>
</field>
<field name="slits" type="NX_INT">
Expand All @@ -74,8 +87,7 @@
<field name="slit_edges" type="NX_FLOAT" units="NX_ANGLE">
<doc>
Angle of each edge of every slit from the position of the
top-dead-center timestamp sensor, anticlockwise when facing
away from the source.
top-dead-center timestamp sensor.
The first edge must be the opening edge of a slit, thus the last edge
may have an angle greater than 360 degrees.
</doc>
Expand All @@ -93,8 +105,7 @@
<field name="beam_position" type="NX_FLOAT" units="NX_ANGLE">
<doc>
Angular separation of the center of the beam and the
top-dead-center timestamp sensor, anticlockwise when facing
away from the source.
top-dead-center timestamp sensor.
</doc>
</field>
<field name="radius" type="NX_FLOAT" units="NX_LENGTH">
Expand Down Expand Up @@ -140,9 +151,9 @@
the source. The reference point in the x and y axis is the point on this surface which is the
centre of the axle which the disk is spinning around. The reference plane is orthogonal to
the z axis and its position is the reference point on that axis.

Note: This reference point in almost all practical cases is not where the beam passes though.

.. image:: disk_chopper/disk_chopper.png
:width: 40%
</doc>
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