User guide
Page 72 Document No: 11294 LBA-USB User Guide
Check Boxes – Specify which results items to graph on the strip chart. One or
all of the following may be selected:
• Centroid X
• Centroid Y
• Peak X
• Peak Y
• Radius
Radius Relative to – Modifies the display of radius information. The radius is
referenced from either an Origin established in LBA-USB or from the continuously
calculated Average Centroid position.
Strip Chart Zooming – All strip chart data is plotted on the same horizontal
and vertical scale. This situation causes traces that vary greatly along the vertical
axes to dominate the vertical scale. Traces that have small vertical fluctuations
show up as flat lines. In order to see these small details, stop or pause data
collection and drag a zooming box around the region of interest. To do this, start
in the top left, drag a box spanning downward and to the right until the region of
interest is selected. More than one zoom operation may be performed to achieve
the desired detail.
Zooming out can only be done once. The plot immediately returns to full view
mode. Zooming out is accomplished by dragging a box from the bottom right
back to the top left. The size of the zoom-out box does not matter since the
operation simply returns the plot to the full view.
Remember: The direction of the zoom operation (in or out) is controlled by the
direction the box is drawn: Down and to the right to zoom in and up and to the
left to zoom out.
Peak and Centroid Scatter Plots and Histograms
There are two ways to use the Scatter Plots in the Beam Stability window.
One is to test stability from the standpoint of spatial dimension using units such
as millimeters or microns. The other is to use it as it relates to pixel units on the
detector array. By electing to view pointing stability using spatial units such as
mm or µm; the bins of the scatter/histogram plot and the horizontal and vertical
grid lines will not have any correlation to the individual pixels on the detector. In
other words, the bins in the histogram and the pixel grid of the detector will not
have the same crosshatch granularity. On the other hand, from the pixel-units
standpoint, the bins on the histogram correlate with the size of the pixel grid on
the detector. There is one drawback, however: in order to obtain real world units
of distance, one must multiply the results by the pixel scale of the detector.
The units on the horizontal and vertical axes of the scatter plots change
depending on LBA-USB configuration. Units could be in microns, millimeters, and
fractions of pixels or any of the other units that are offered in LBA-USB. In short,
the units on the X/Y-axes of the histogram/scatter plots are the same as the
units selected in LBA-USB for quantitative results. Select these units by returning
to LBA-USB and find Pixel Units in the Camera dialog box of the Options
menu.
For example, to see which pixels on the camera most often contained the peak
energy of the beam, setup the histogram bins to work in terms of individual