MIPS 24um Voffset Stability

Principal: dmkelly
Deputy: TBD
Data Monkey(s):
Priority: Necessary
Downlink Priority: Normal
Analysis Time: 12h
Last Updated:

Objective

Determine the stability of the MIPS 24um array offset levels.

Description

In ground testing, we observed that the offset level of the 24um data ramps was highly variable during a warmup period that lasted at least 48h. Performing a thermal anneal seemed to bring the array immediately to the final, stabilized level. What we don't know is whether the offset values are stable on week-long timescales or in a radiation environment. That is what we will probe in this study. The important data will be pre-anneal and post-anneal RAW data taken at the end of the campaign. If necessary, we will start to collect a small amount of RAW data following the thermal anneal at the start of each campaign.

Data Collected

mips_raw_C0F2N10 (x2) 

mips_mobs_phot
sendcmd CEGESTIM '"AUTO",63,"BOTHOFF","BOTHOFF","BOTHOFF",10,10,"MIPS"'
sendcmd CEGERSTCON '10,127,4,"MIPS"'
sendcmd CESCANCON '"CHOP","REV",0,2048,2048,0,511,"MIPS"'
# collect 10 4s RAWs
sendcmd CEMIPSRAW  'AORID_upper,AORID_lower,0,"NO_COADD",2,10,"MIPS"'
MIPS_BACKTO_MOBS
# Thermal anneals on Si array
  ColDiag_24TMP_MIPS
    Si_Anneal_Heat_MIPSA_MIPS
  CEDumpDiag
# post-anneal exposure
MIPS_MOBS_PHOT
sendcmd CEGESTIM '"AUTO",63,"BOTHOFF","BOTHOFF","BOTHOFF",10,10,"MIPS"'
sendcmd CEGERSTCON '10,127,4,"MIPS"'
sendcmd CESCANCON '"CHOP","REV",0,2048,2048,0,511,"MIPS"'
# collect 10 4s RAWs
sendcmd CEMIPSRAW  'AORID_upper,AORID_lower,0,"NO_COADD",2,10,"MIPS"'
mips_backto_mobs

Data Reformatting Requirements

Array Data Desired:

24um array

Data Reformatting Option:

Special Instructions:
Each set of 10 DCEs should go in a separate file.

Task Dependencies

Calibration Dependencies

Output and Deliverable Products

Median and minimum ramp starting points both pre- and post-anneal.

Data Analysis

Step by step analysis:
1) Create a file list.  Use imstat in IRAF or some other tool to determine
   median and minimum values for the first sample in each of the 20 DCEs.
2) Compare the mean starting points from the pre-anneal data with the mean
   values from the post-anneal data.  
3) If there is a change, assess whether the change is large enough that we 
   will ever have to worry about the ramps starting below the bottom rail 
   of the A-D converter.

Software Requirements

A tool is needed that allows you to calculate median and minimum values for a single Si frame. A telemetry extraction tool should be available. Plotting tools are also likely to be useful.

Actions Following Analysis

Produce a brief report describing the behavior of the 24um offsets. If necessary, determine a new set of offset voltages and apply them for use in future campaigns by making changes to irs-mips_pconst_ier. Decide whether additional 24um anneals are warranted.

Failure Modes and Responses

If the starting points of the data ramps change a lot over long timescales or in a radiation environment, we might need to change the 24um offset voltages to ensure that all of our data are on-scale. This means sacrificing a bit of our dynamic range. We will also need to assess whether additional 24um anneals are warranted.

Additional Notes

Additional Notes:

In ground testing, if a thermal anneal is performed first, the starting 
points for the 24um data ramps seem to be quite stable.  The values drift 
by maybe 100-200 DN over 12 hours, which is very small compared to the 
gain of 1400 DN per offset DAC count.  Since the pixel with the lowest 
ramp starting point is offset by about 2300 DN from the median, the 
median starting point should be set no lower than -30500 DN.  In practice, 
our offset of 0x6b puts the lowest pixel with CE-2 at a starting point of 
about -31250 DN and the array median at -28950.  For CE-1, the lowest 
pixel starts at -31050 and the median is -28800.  For both CEs, a 
downward shift of another 1400 DN would be unacceptable.

The following ramp starting values were registered on the 24um array during
Brutus testing.  I used tabulate to extract CE temperatures.  24um anneals
were performed on all of these test days, and all data were measured with
an offset DAC setting of 0x6b.  All data are dark frames.  From stim data
not presented here, there is evidence that the starting points are of
order a few hundred counts lower when a modest brightness stim is running.
From the CE2 data, it appears that the ramp starting points decrease with
increasing CE temperature, with a change of about 600-800 DN for a CE
temperature change of 40C.  The scatter at a given temperature is several
hundred DN.  These conclusions are based on only the small amount of data
presented below.

Day       CE    Median    Minimum     CETmp  D160BoardTmp  D70BoardTmp  Comments
01-220     1    -28034    -30283      13.5        30.3        20.1
01-263     2    -28919    -31393      32.1        44.4        30.3
01-265     2    -29072    -31929      29.8        41.9        27.9
01-284     2    -28282    -30793     -11.7         6.3        -5.2
01-285     2    -28458    -30958     -12.4         5.6        -5.8
01-286     1    -27909    -30266      10.8        26.9        17.1
01-289     2    -29658    -32222     -14.2         3.7        -7.7  1st obs.

ATLO Test data:
02-088     2    -29125    -31613      29.6        41.3        27.9
02-108     2    -28652    -30894      25.2        37.9        24.1