BD FACSAria - Page 64

64 BD FACSAria User’s Guide
Breakoff Window
The upper camera transmits an image of the drop breakoff to the
Breakoff window, where video image processing software
converts the visual characteristics of the image into numerical
properties. The drop breakoff is analyzed for two key features:
Drop 1 and Gap.
Drop 1 is defined as the number of pixels from the top of the
image to the center of gravity of the first broken-off drop. A thin
gray line on the image is used to identify this drop. The number
shown to the right of the Drop 1 field at the bottom of the
window is the actual pixel location of the gray line. The number
entered into the Drop 1 field is the user-defined Drop 1 target.
The Gap is defined as the number of pixels from the first
discontinuity in the stream to the next stream object, generally the
first broken-off drop. A gray line of varying thickness represents
the Gap. The number shown to the right of the Gap field is the
pixel width of the gray line. The number entered into the Gap
field is a user-defined target.
When the Sweet Spot is turned on, the drop drive amplitude
(Ampl.) is automatically adjusted to approximately match the
target Drop 1 and Gap values. The amplitude is initially adjusted
in larger increments until Drop 1 is achieved. The amplitude is
then adjusted in smaller increments until the cytometer attains the
target Gap. The Sweet Spot feature will make adjustments as
necessary to maintain the required breakoff conditions
throughout the day.
The Sweet Spot performs two other functions during sorting.
When sorting, if the Drop 1 or Gap are out of range, sorting is
paused until the values are back within range. This ensures that
sorting occurs only under the proper breakoff conditions. If a
more severe problem such as a clog is detected by the Sweet Spot,
the stream is shut off and sorting is stopped: the deflection plates
shut off, the aspirator drawer closes, and the sample tube is unloaded.
Drop 1
Gap
actual
value
target
value