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64 PI-MAX
®
4 System Manual Issue 4
5.3.2 Cleaning
The basic cleaning function is implemented by clean cycles. These cycles start when you
turn the camera on and a clean pattern is programmed into the camera. Their purpose is to
remove charge that accumulates on the array while the camera not acquiring data (i.e.,
exposing and reading out the array.) The timing diagram below is for an experiment set up to
acquire three (3) images using Internal trigger mode selected on
SuperSYNCHRO Trigger In
tab {
Trigger expander} and Gate Mode selected on Experiment Setup Main tab {In
LightField, the equivalent of Gate Mode is active when
Enable Intensifier is checked on the
Common Acquisition Settings expander}. In Figure 5-2, clean cycles occur before the first
exposure and after the last readout period. They do not need to occur between exposures since
each readout cleans the array before the next exposure starts.
Figure 5-2: Clean Cycles in Internal Trigger Mode of Operation
The configuration of clean cycles is performed on the Hardware Setup —> Cleans/Skips
tab {via the
Sensor Cleaning pane accessed on the Sensor expander}. When you set up
the camera for the first time, default values are automatically inserted into these fields.
These will give the best results for most applications. Even so it is a good idea to know what
these entries mean with regard to cleaning.
• Number of Cleans {Number of Clean Cycles} value is usually set to one (1.)
These are additional clean cycles that can be required after a start exposure signal is
received and the current clean cycle has finished. The maximum value for this entry
depends on the camera.
• Number of Strips per Clean {Clean Cycle Height} sets the number of rows that
will be shifted and discarded per clean cycle. While a large number such as the number
of rows in the array may result in the best cleaning of the array, the trade off is that there
may be a significant delay between the receipt of a start exposure signal and the
beginning of the actual exposure. This delay occurs because the current clean cycle
must be completed before a start exposure signal received during the cycle will be
implemented. Typically, the default setting is much smaller and in time critical
experiments, the setting should be 1 or 2.
• Continuous Cleans {Clean Until Trigger} is available when the start of exposure
is tied to an external trigger. In WinX, this cleaning becomes active when
External
Sync
timing mode is selected. In LightField, it becomes active when Trigger
Response
is set to Readout Per Trigger or Shift Per Trigger.
Clean
Cycle
Photocathode
Shutter (Normal)
Biased On
Clean
Cycle
t
c
Logic Out: Read Out
{Reading Out}
Biased Off Biased On Biased Off Biased On Biased Off
ET = exposure time set in Experiment Setup
t
c
= 3 msec shutter compensation for Electronic shutter
ET
Image
Acquired
CCD
Readout
Image
Acquired
CCD
Readout
Image
Acquired
CCD
Readout
t
c
ET
t
c
ET
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