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VIRCAM: Detector dark current
 
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dark current
QC1 database (advanced users): browse | plot

The darkcurrent calibration is a technical calibration. It is not used to calibrate other calibrations or science data. The darkcurrent template acquires a sequence of dark frames with different DITs. The pipeline recipe fits the relation darkcurrent( DIT ). While the dark level retrieved from the dark recipe gives the dark counts in ADU for a master dark of a given DIT, the darkcurrent gives the current in ADU/sec in a more accurate manner.


Dark current

QC1_parameters

FITS key QC1 database: table, name definition class* HC_plot** more docu
QC.DARKCURRENT vircam_current..qc_darkcurrent median dark current [ADU/s] CAL [docuSys coming]
*Class: KPI - instrument performance; HC - instrument health; CAL - calibration quality; ENG - engineering parameter
**There might be more than one.

The QC.DARKCURRENT gives the dark current (the dark flux) in ADU/sec.

QC report of a dark current technical calibration with the linear fit to the dark counts versus exposure time relaetion. click in the image to see dark current fit of all detectors.

Each detector has its own dark current. There following map shows the values in ADU/sec (June 2010):

chip13
chip 14
chip 15
chip 16
0.405
0.221
0.030
0.052
chip 9
chip 10
chip 11
chip 12
0.065
0.038
0.059
0.053
chip 5
chip 6
chip 7
chip 8
0.066
0.079
0.090
0.097
chip 1
chip 2
chip 3
chip 4

0.296

3.000
0.476
0.355

red labels mark detectors with relatively high dark current, green labels mark detectors with relatively low dark current.

Trending

Upper left plot shows the average over 16 detector-specific values, the lower left box shows the rms over 16 detectors, the upper right plot shows 16 individual detector values, and the lower right plots shows the detector specific scores.

Scoring&thresholds Dark current

According to the 2018 version of the VIRCAM key performance indicator (KPI) document, the dark current must be lower than 2 ADU/sec for an individual chip.

History

  • 2018-06-01: the detector temperature was modified from 75 K to 72 K. As a result the dark current decreased.

Algorithm Dark current

The dark counts versus exposure time is fit by a linear function. The gradient of the fit is the darkcurrent QC parameter.


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