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VIRCAM Quality Control:
detector linearity

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non-linearity parameters
 
QC PLOTS
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detector non-linearity
fraction of bad pixels
flux variation
QC1 database (advanced users): browse | plot
   Click on CURRENT to see the current trending (Health Check).
   Click on HISTORY to see the historical evolution of the trending.


top non-linearity

QC1 parameters

parameter QC1 database: table, name procedure
qc_linearity vircam_line, qc_linearity, qc_linerror, qc_nbadpix, qc_badfrac - The non-linearity is derived from a series of dome flat exposures with different flux levels. The reference flux is at 10000 ADU. qc_linearity is the percentage of non-linearity at 10000 ADU.

halogen lamp performance

vircam_line, qc_screen step, qc_screen_total - The calibration unit consists of several halogen lamps illuminating a screen in the VISTA enclosure. Both parameters monitor intrinsic illumination instabilities and failures of individual lamps.

 

top ranges and saturation

QC1 parameters

parameter QC1 database: table, name procedure

qc_line_medmin , qc_line_medmax

vircam_line, qc_line_medmin, qc_line_medmax - The post-pipeline QC script measures the mode flux in all flat frames. The highest flux and the lowest mode flux of all raw flat frames is taken. (mode means: the maxium of the flux histogram is taken.). Since the detector is operated in double correlated read out mode, which is composed by three sequential events: reset, read read. The detector requires DET.MINDIT seconds to reset and read all pixel of the detector. DET.MINDIT=1.0011 sec (2009-12-01). The detector acquisition system subtracts the flux taken between the reset and the first read from the flux measured after the second read and writes it into the frame. Hence the measured flux in a flat does correspond to DIT seconds exposure time. For reasons to check the flux versus the saturation level, the flux acquired in DIT + MINDIT seconds must be compared. The qc_lin_medmin and qc_line_medmax are corrected for the DIT+MINDIT exposure times:
qc_line_medmax = flux * (DIT+MINDIT)/DIT.
The correction is only relevant for small DIT, large lamp fluxes, and large MINDIT.

dit_min, qc_dit_max

vircam_line, qc_dit_min, qc_dit_max - The post-pipeline script takes the largest and the smallest used DET.DIT from the linearity sequence


Saturation

Each detector has a different saturation level. The saturation levels in ADU are (2009-09):

chip13 chip 14 chip 15 chip 16
33000 35000 34000 34000
chip 9 chip 10 chip 11 chip 12
35000 35000 37000 34000
chip 5 chip 6 chip 7 chip 8
24000 36000 35000 33000
chip 1 chip 2 chip 3 chip 4

33000

32000 33000 32000

Detector #5 has the lowest saturation level

From 2009-11-20 on, ( after the video channel card replacement for chip #6 ) the saturation levels are:

chip13 chip 14 chip 15 chip 16
33000 35000 34000 34000
chip 9 chip 10 chip 11 chip 12
35000 35000 37000 34000
chip 5 chip 6 chip 7 chip 8
24000 27000 35000 33000
chip 1 chip 2 chip 3 chip 4

33000

32000 33000 32000

 


 
 
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