INT Duty Engineer Checks
The Wide Field Camera (WFC) Sensitivity Check with UltraDAS

Reason

The purpose of this document is to provide a simple check on the sensitivity of the four CCDs that comprise the WFC.  The check involves taking a flatfield and determining the number of counts that appear in each CCD image.

Procedure

1. Switch on the main dome lights.
2. Select an appropriate filter from table 1.
3. Position the telescope as indicated in table 1.
4. Take a flat exposure using the appropriate integration time. Use the  command
   SYS> flat xx
   where XX is the integration time.
5. Display the image in IRAF using the wfc_disp command.  Prior to doing this it may be wise to use the IRAF "unlearn display" command to clear any custom display parameters.
6. From the associated output in the IRAF xgterm window, check that the MIDPT values (median of counts) of the four CCDs do not differ significantly.  They should be within about 20% of each other.  If a factor of 2 or greater exists, this represents a problem which should be reported to the detector specialists.

This is an example of the expected output :

ing> wfc_disp r443886
Displaying image of CCD4 in frame 4 ....
z1=12641.33 z2=15143.
#               IMAGE     MIDPT    STDDEV     MIN       MAX
            r443886[4]    14010.    3258.     1369.    65535.
Displaying image of CCD3 in frame 3 ....
z1=11783.5 z2=16474.
#               IMAGE     MIDPT    STDDEV     MIN       MAX
            r443886[3]    15593.    3931.     1276.    65535.
Displaying image of CCD2 in frame 2 ....
z1=9037.232 z2=13360.
#               IMAGE     MIDPT    STDDEV     MIN       MAX
            r443886[2]    12245.    2823.     1263.    65535.
Displaying image of CCD1 in frame 1 ....
z1=10839.54 z2=13612.
#               IMAGE     MIDPT    STDDEV     MIN       MAX
            r443886[1]    12799.    2949.     1269.    43344.

Table 1

Document History

Rev 0.1 Draft issue: Nov 27^th 2006  Don Carlos Abrams
Rev 1.0 Release issue: Nov 28^th 2006  Don Carlos Abrams
 

This file:  http://www.ing.iac.es/~eng/ops/int/wfc_sensitivity.html