Spyder3 GigE Vision SG-14 Monochrome Cameras User’s Manual
55
Teledyne DALSA
03-032-20123-01
Appendix A: Clear 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 total 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 ch arge accu m u lated in the gates. Even w ith exp osu re control on, at low line rates, this
gate ch arge 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.
N ote:
When au to clear is ON in the H S, d u al line m od e, the lead ing TDI stage is transferred sep arately
and stored in the cam era m em ory. TDI su m m ing is recreated by ad d ing stored d ata to the trailing TDI
stage in the cam era p rocessing ch ain. Du e to d igital su m m ing, d ark noise w ill increase by √2. A d igital
ad d w ill not increase d om inant shot noise.
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 the cam era w ill
au tom atically start and stop d ark cu rrent clear , d ep end ing on 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 27: 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, the d ark cu rrent clear sw itch over is controlled
by hysteresis threshold s. Threshold s (LF and H F) are set to higher frequ encies, 30-45% of the m axim u m
line rate, so 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, then a corru p ted line w ill occu r .
Threshold frequ encies for each m od el are ou tlined in the tables below .
Table 12. Auto readout mode thresholds
HS Mode
Transition Frequencies (Hz)
Model
LF
HF
Maximum Line Rate
SG-14-01K40-00-R
9818
11230
36000
SG-14-01K80-00-R
18149
20747
68000
