Background

Over time, the bias levels of the CCDs in the DEIMOS science mosaic will drift from the nominal value of 1000 DN/px. The required adjustments can be completed easily and quickly through the procedure described below, which will produce new values for the VIDOFFn keywords controlling the bias level.

Procedure

Adjust VIDOFF keywords for B amplifiers

  1. Launch DEIMOS control software as any DEIMOS numbered account on its corresponding VNCs.
  2. On any DEIMOS Linux host terminal, excute the command:
    deimos_check_vidoff -iter 6 -ampmode B -mosmode spectral
    This procedure will:

Save values

When new bias levels are determined, they should be recorded in the deimosplus.VIDOFF keyword so that these values get re-loaded by the observer each afternoon. To do so, on any DEIMOS Linux host terminal, as any DEIMOS numbered account:

modify -s deimosplus vidcap=Yes

Confirm values

On any DEIMOS Linux host terminal, as any DEIMOS numbered account:

show -s deimosplus vidoff
The video offset values on the keyword should match the output from the last iteration of the deimos_check_vidoff script.

Repeat the same steps for A amplifiers

On any DEIMOS Linux host terminal, excute the command:

deimos_check_vidoff -iter 6 -ampmode A -mosmode spectral
Once the script is done, save the values on the deimosplus.VIDOFF keyword and verify they have been properly saved.

Example of deimosplus.VIDOFF output

 [deimos5@deimos ~]$ gshow -s deimosplus vidoff
    VIDOFF = deiccd.VIDOFF1 2515 deiccd.VIDOFF2 2445 
    deiccd.VIDOFF3 2320 deiccd.VIDOFF4 2516 deiccd.VIDOFF5 2551 
    deiccd.VIDOFF6 2549 deiccd.VIDOFF7 2508 deiccd.VIDOFF8 2588 
    deiccd.VIDOFF9 3208 deiccd.VIDOFF10 2772 deiccd.VIDOFF11 2131 
    deiccd.VIDOFF12 2538 deiccd.VIDOFF13 2435 deiccd.VIDOFF14 2428 
    deiccd.VIDOFF15 2441 deiccd.VIDOFF16 2453