Teledyne ProEM Series, System Manual

Page: 92 / 162

92 ProEM System Manual Issue 3
6.1.4 External Sync with Continuous Cleans {Clean Until Trigger} Timing
Another timing mode available with the ProEM is called Continuous Cleans {Clean Until
Trigger}. In addition to the standard cleaning of the array, which occurs after the
camera is enabled, this mode will remove any charge from the array until the moment
the External Sync pulse is received. See
Figure 6-4 .
Figure 6-4: Flowchart: Continuous Cleans {Clean Until Trigger}
Once the External Sync pulse is received, cleaning of the array stops as soon as the
current row is shifted, and frame collection begins. With Normal {Normal} shutter
operation, the shutter is opened for the set exposure time. With PreOpen {Open Before
Trigger} shutter operation, the shutter is open during the Continuous Cleaning {Clean
Until Trigger}, and once the External Sync pulse is received the shutter remains open for
the set exposure time, then closes. If the vertical rows are shifted midway when the
External Sync pulse arrives, the pulse is saved until the row shifting is completed, to
prevent the CCD from getting out of step. As expected, the response latency is on the
order of one vertical shift time, from 1-30

s depending on the array. This latency does
not prevent the incoming signal from being detected, since photo generated electrons
are still collected over the entire active area. However, if the signal arrival is coincident
with the vertical shifting, image smearing of up to one pixel is possible. The amount of
smearing is a function of the signal duration compared to the single vertical shift time.
Shutter opens
CCD is continuously
cleaned until External Sync
pulse is received
Shutter remains open
for preprogrammed
exposure time
System waits while
shutter closes
Data is read out of
the array
(shutter preopen) (shutter normal)
CCD is continuously
cleaned until External Sync
pulse is received
Shutter opens
441
1-
0
12
6
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0
0
4
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