User guide

LBA-USB User Guide Document No: 11294 Page 95
remain the same, and the camera black level, shading and noise conditions do
not change.
Since most cameras tend to be a little drifty, we recommend performing an
Ultracal! cycle every 10 to 15 minutes, or whenever you think the camera may
have strayed. This drift can be observed as changes to the background noise
image. Un-illuminated areas appear as gray and dark violet (almost black)
random noise. If the background starts to look too gray, then the baseline is
drifting negative; if too dark, then the baseline is drifting positive.
Note: These colors apply to the Continuous 128 color palette. The color shading
changes depending upon the palette selection, but the principle remains the
same.
4.5 Clip Level
The clip level is a processed energy pixel value. Only those pixel values that exceed the
clip level are used in computing the following results:
 Beam Widths, if Percent of Energy or Peak methods are selected
 Centroid Location
 Elliptical beam Orientation
 Top Hat: Mean, Standard Deviation, Min and Max, when in Data mode only
 Effective Area
Depending on the Beam Width Method selected, the clip level value is determined as
follows:
 With the 4-Sigma and Knife-Edge methods and with the Top Hat results disabled,
LBA-USB totals the pixel
energy values in descending order until it finds the pixel which
causes the sum to exceed 86.5% of the total
energy value. The raw energy value of this
pixel becomes the clip level.
 With the 4-Sigma and Knife-Edge methods and with the Top Hat results enabled,
LBA-USB sets the clip level to the value that is equal to 80% of the current peak energy
value.
 With the Percent of Energy method, LBA-USB totals the pixel energy values in
descending order until it finds the pixel that causes the sum to exceed the set Clip% of
the total
energy value. The energy value of this pixel becomes the clip level.
 With the Percent of Peak method, LBA-USB sets the clip level to the value that is equal
to the set Clip% of the current peak
energy value.
The number of pixels with values above the clip level establishes the Effective Area of
the beam. The locations of the pixels with values above the clip level are used to
determine the beam's Centroid Location and Elliptical Beam Orientation.
Note: When using a Knife Edge method, the Clip% value relates only to the Knife
Edge measurement process, and not to the above Clip Level description.
4.6 Total Energy
The cameras used with LBA-USB are not calibrated to directly provide the energy of a
laser beam. The Energy of Beam dialog box allows the user to calibrate LBA-USB to