54
•
Appendix A: Clear Dark Current
Immediate read out mode (default, srm 2)
In this mode the image is read out, including accumulated dark current, immediately
following the trigger or the EXSYNC falling edge.
There are no line rate limitations other than the amount of gate dark current that can be
tolerated at low line rates.
For information on artifacts that may be experienced while using this mode, see the
Artifacts section below.
There are no timing or exposure anomalies other than situations where EXSYNC is removed
from camera. In this case, the camera can be set to operate in a "watchdog" state.
The watchdog will start DC clear at frequencies = or < 10 Hz, where dark current is
significant.
A small DN step will be visible in the image where the watchdog turns on and off.
The watchdog operates on the single threshold. If sync frequency is not in the sharp
transition watchdog may cause corrupted lines crossing the threshold.
Gate dark current clear mode (always on, srm 1)
In this mode the gate dark current will be cleared continuously.
After the trigger (EXSYNC) is received, the dark current is cleared from the image sensor
before the image is acquired. The line rate is limited to ½ the maximum line rate available
for that model of camera.
For information on artifacts that may be experienced while using this mode, see the
Artifacts section below.
Table 12. Maximum Line Rates
Model
Max. Line Rate
Immediate Readout Mode
Dark Current Clear Mode
SG-34-02K80
18000 Hz
9000 Hz
SG-34-04K80
9000 Hz
4500 Hz
When operating in the dark current clear mode, there will be a slight delay, equivalent to
one readout time, before the actual exposure is implemented. The actual exposure time will
not be altered.
Table 13. Exposure Delay and Maximum Exposure Times
Model
Exposure Delay and Max Exposure Time in Auto Mode
SG-34-02K80
55.5 µs
SG-34-04K80
111 µs
Setting the Readout Mode
Use this command to control dark current in the vertical transfer gates.
Camera Link Command
Parameter
Description
Notes
srm
0
: Auto. Clears dark current
below ~ 30-45% of the maximum
line rate
1
: Dark current clear. Always
clears dark. Reduces the
maximum line rate.
•
The vertical transfer gates collect dark
current during the line period. This
collected current is added to the pixel
charge.
•
If the user is in
sem 2
or
7
and
srm 2
,
with
ssf
at 45% of the maximum, and