Specifications
Appendix G Interline CCD Cameras 85
time the controller waits for the first External Sync pulse, plus t
exp
, the programmed exposure
time, plus t
c
,
the shutter compensation time (zero with None selected as the Shutter type), then
the actual exposure time will equal t
R
. If an External Sync pulse is detected during each read,
frames will follow one another as rapidly as possible as shown in Figure 41. In the figures that
follow, Shutter Monitor indicates the programmed exposure time. If a shutter were present
and active, it would also be the actual exposure time.
Prior to the first readout, clean cycles are performed on the array. When the software
issues a Start Acquisition command, the first exposure begins. Time counting of the
programmed Exposure Time begins when the sync pulse arrives at the Ext Sync
connector. The exposure ends on completion of the programmed Exposure Time. Then
the data acquired during the first exposure is read out while the next frame of data is
being acquired. This pattern continues for the duration of the experiment so that, during
each frame, the data acquired during the previous frame is read out.
SCAN
Shutter
Monitor
External Sync
(negative polarity shown)
t
exp
t
w1
50ns min.pulse between frames
t
R
t
R
t
R
t
R
actual exposure time
cleans
acquisition
Figure 41. Overlapped mode where t
w1
+ t
exp
+ t
c
< t
R
Figure 42 shows the case where the programmed exposure time is greater than the time
required to read out the storage half of the array, that is, where t
w1
+ t
exp
+ t
c
> t
R
. In this
case, the programmed exposure time will dominate in determining the actual exposure
time. In the situation depicted in Figure 42, the External Sync pulse arrives during the
readout. As always, the External Sync pulse must be detected before the next readout can
occur. However, there is no requirement as to when it must be applied or even that it be
periodic. The timing of the External Sync pulse is entirely at the your discretion. In
Figure 43, the External Sync pulse is shown arriving after the read. Detection of the
External Sync pulse enables a new readout to occur on completion t
exp
+ t
c.
SCAN
Shutter
Monitor
External Sync
(negative polarity shown)
t
exp
t
w1
t
R
t
c
cleans
acquisition
t
R
t
R
t
R
t
R
actual exposure time
Figure 42. Overlapped mode where t
w1
+ t
exp
+ t
c
> t
R