DEIMOS Bias Level Adjustment Procedure

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

Launch DEIMOS control software as any DEIMOS numbered account on its corresponding VNCs.
On any DEIMOS Linux host terminal, excute the command:
```
deimos_check_vidoff -iter 6 -ampmode B -mosmode spectral
```
This procedure will:
- configure DEIMOS in spectral mode using the B amplifiers,
- acquire bias images,
- analyze them for offsets in bias level,
- make appropriate adjustments to the CCD keywords to equalize the bias

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

	DEIMOS Bias Level Adjustment Procedure
DEIMOS Home Page NEWS Config form Slitmask database DEIMOS temps (internal) Index Keck Instrument Ready? Archive (KOA) Observer Home Page Tel Schedule Instruments Home Keck Home Observing Info ToO Policies Weather MK Forecast CFHT SkyProbe MK Seeing CFHT Cloudcam Summit Cams Keck Cloud Cams Planning Tools Starlist Tool Finding Charts IRSA Finder Charts Observing Planning Tool Offset/PA Tool Contact Us Contact Info Post-Observing Comment Form WWW Keck Web Site	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 Launch DEIMOS control software as any DEIMOS numbered account on its corresponding VNCs. On any DEIMOS Linux host terminal, excute the command: deimos_check_vidoff -iter 6 -ampmode B -mosmode spectral This procedure will: configure DEIMOS in spectral mode using the B amplifiers, acquire bias images, analyze them for offsets in bias level, make appropriate adjustments to the CCD keywords to equalize the bias 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
Last modified: 05/05/2021 22:59 Send questions or comments to:DEIMOS Support