50 Spyder3 SG-34 GigE Vision Color Manual
03-032-20124-00 Teledyne DALSA
Appendix A: Clear Dark Current
Setting the Readout Mode
Refer to the Clearing Dark Current section for more information on this feature.
Use the Readout Mode feature (from the Sensor Controls set) to clear out dark current charge in the
vertical transfer gates immediately before the sensor is read out.
The available readout modes are Auto, Dark Current, and Immediate Readout.
Auto: Clears dark current below ~ 45% of the maximum line rate. (Default mode.)
Dark Current Clear: Dark current clear. Always clears dark. Reduces the maximum line rate.
Immediate Readout: Immediate readout. Does not clear dark current.
Notes:
ï‚· The vertical transfer gates collect dark current during the line period. This collected current is added
to the pixel charge. This additional charge is especially noticeable at slower line rates.
ï‚· This value is saved with the camera settings.
ï‚· If the user is using internally programmable line rate and exposure time, or internally programmable
line rate and maximum exposure time, and immediate read out mode, with Acquisition LineRate
Abs at 45% of the maximum, and then ReadoutMode 1 is selected, the following warning will be
displayed, but the AcquisitionLineRateAbs value will not be changed: Warning 09: Internal line rate
inconsistent with readout time> The effect in both internal and external line rate modes is that an
EXSYNC is skipped and, therefore, the output will be at least twice as bright.
Gate Dark Current Clear
Image sensors accumulate dark current while they wait for a trigger signal. If the readout is not triggered
in a reasonable amount of time, then this dark current accumulation may increase to an excessive
amount. The result of this happening will be that the first row, and possibly additional rows (lines), of the
image will be corrupt.
The sensor used in the Spyder3 GEV camera contains two sources of dark current that will accumulate
with time: 1) in the photo sensitive area, and 2) in the gates used to clock-out the charge.
The gate dark current can account for approximately 20% of the total dark current present. While th e
exposure control has direct control over the amount of dark current in the photo sensitive area, it has no
control over the charge accumulated in the gates. Even with exposure control on, at low line rates, this
gate charge can cause the camera to saturate.
Using the Readout Mode command, the camera user can control the camera's behavior in order to
minimize the dark current artifact.
The modes of operation selected by the Readout Mode command are: Auto, On, or Off.
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