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Spyder3 SC-34 Color Camera User's Manual
03-032-20116-01
Teledyne DALSA
Clearing Dark Current
Gate Dark Current Clear
Im age sensors accu m u late d ark cu rrent w hile they w ait for a trigger signal. If the read ou t is not triggered
in a reasonable am ou nt of tim e, then this d ark cu rrent accu m u lation m ay increase to an excessive
am ou nt. The resu lt of this hap p ening w ill be that the first row , and p ossibly ad d itional row s (fram es), of
the im age w ill be corru p t.
The sensor u sed in th is cam era contains tw o sou rces of d ark cu rrent that w ill accu m u late w ith tim e: 1) in
the p hoto sensitive area, an d 2) in the gates u sed to clock-ou t the charge.
The gate d ark cu rrent can accou nt for ap p roxim ately 20% of the to tal d ark cu rrent p resent. While the
exp osu re control has d irect control over the am ou nt of d ark cu rrent in the p hoto sensitive area, it has no
control over the charge accu m u lated in the gates. Even w ith exp osu re control on, at low line rates, this
gate charge can cau se the cam era to satu rate.
Using the
Set Readout Mode (srm)
com m and , the cam era u ser can control the cam era's behavior in
ord er to m inim ize the d ark cu rrent artifact.
The m od es of op eration selected by the
srm
com m and are: Au to, On, or Off.
Auto Mode (srm 0)
N ote: Teled yne DALSA recom m end s Au to m od e for m ost u sers. In this m od e cam era w ill au tom atically
start and stop d ark cu rrent clear based on the line rate.
Stop
Max line rate
DC Clear th
HF
LF
Watchdog th
100Hz
DC Clear ON
DC Clear OFF
Freq decreasing
Freq increasing
Figu re 20: Gate Dark Cu rrent Clear in the Au to Mod e.
To avoid corru p ted lines d u e to jitter in External Trigger m od e, the d ark cu rrent clear sw itchover is
controlled by hysteresis threshold s. Threshold s (LF and H F) are set to higher frequ encies, below ½ of the
m axim u m line rate, so th at sw itchover w ill be transp arent in an im age.
H ow ever, if the external trigger frequ ency ju m p s back and forth over both threshold s in three consecu tive
lines, a corru p ted line w ill occu r.
Threshold frequ encies for each m od el are ou tlined in the tables below .
Auto Mode
Transition Frequencies (kHz)
Model
LF
HF
Maximum Line Rate
SC-34-02K80-00-R
7433
8993
18000
SC-34-04K80-00-R
4000
4400
9000
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