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Features & Functionality
The third keep clean is the External Keep Clean Cycle. This cycle uses a different sequence of horizontal and vertical
clocking as it must be able to respond to external events extremely rapidly, but at the same time keep the Image area
of the sensor charge free. As can be seen from the gure below, the external keep clean cycle consists of a continuous
cycle of one vertical shift, both Image and Storage, followed by one horizontal shift. When an external trigger is detected
the current cycle will complete before the exposure phase starts. It is worth noting that although the external keep
clean cycle will complete the current cycle, this will not result in the total loss of signal as only one vertical shift will have
occurred. For pulsed light of very short time duration, microseconds (i.e. of the order of one vertical shift), the resultant
image may appear to have shifted one row.
NOTE: The 885 range of iXon3 cameras have a global clear feature which can be used to remove all the charge
accumulated in the whole Image section of the sensor simultaneously. This feature is enabled in all 885 models
when external trigger is selected. It is particularly useful in external trigger mode when the light level pre-trigger
is quite bright as it will reduce the effect of vertical streaking.
Figure 27: External Trigger Keep Clean Cycle
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