MIPS 24um Voffset Adjustment Test

Principal: dmkelly
Deputy: jmuzerolle
Data Monkey(s): No, but we could use some data lizards
Priority: Necessary
Downlink Priority: Normal
Analysis Time: 4h
Last Updated:

Objective

Determine the optimum values for the MIPS 24um array offset DACs.

Description

To maximize the dynamic range of the 24um detector, we want to start the data ramps fairly close to the lower rail of the A-D converter. At the same time, to obtain accurate slopes, it is essential that no pixel have a data ramp starting point of less than -32768 DN. In ground-based testing, we determined optimal DAC settings for the offset voltage DACs to meet these criteria. In this test, we will confirm those settings.

Data Collected

mips_raw_C0F2N5 (x6) 

mips_mobs_phot
CESCANPOS '101,"MIPS"'
CEGESTIM '"AUTO",63,"BOTHOFF","BOTHOFF","BOTHOFF",10,10,"MIPS"'
CEGERSTCON '10,127,4,"MIPS"'
CESCANCON '"CHOP","REV",0,2048,2048,0,511,"MIPS"'
# Voffset=0x6B
CEMIPSRAW '0x0,0x0,0,"NO_COADD",2,5,"MIPS"'
CELDTPGIF '0x02,0x6A,"MIPS"'
CELDTPGIF '0x03,0x6A,"MIPS"'
CELDTPGIF '0x04,0x6A,"MIPS"'
CELDTPGIF '0x05,0x6A,"MIPS"'
CEMIPSRAW '0x0,0x0,1,"NO_COADD",2,5,"MIPS"'
CELDTPGIF '0x02,0x69,"MIPS"'
CELDTPGIF '0x03,0x69,"MIPS"'
CELDTPGIF '0x04,0x69,"MIPS"'
CELDTPGIF '0x05,0x69,"MIPS"'
CEMIPSRAW '0x0,0x0,2,"NO_COADD",2,5,"MIPS"'
CELDTPGIF '0x02,0x68,"MIPS"'
CELDTPGIF '0x03,0x68,"MIPS"'
CELDTPGIF '0x04,0x68,"MIPS"'
CELDTPGIF '0x05,0x68,"MIPS"'
CEMIPSRAW '0x0,0x0,3,"NO_COADD",2,5,"MIPS"'
CELDTPGIF '0x02,0x6C,"MIPS"'
CELDTPGIF '0x03,0x6C,"MIPS"'
CELDTPGIF '0x04,0x6C,"MIPS"'
CELDTPGIF '0x05,0x6C,"MIPS"'
CEMIPSRAW '0x0,0x0,4,"NO_COADD",2,5,"MIPS"'
CELDTPGIF '0x02,0x6D,"MIPS"'
CELDTPGIF '0x03,0x6D,"MIPS"'
CELDTPGIF '0x04,0x6D,"MIPS"'
CELDTPGIF '0x05,0x6D,"MIPS"'
CEMIPSRAW '0x0,0x0,5,"NO_COADD",2,5,"MIPS"'
CELDTPGIF '0x02,0x6B,"MIPS"'
CELDTPGIF '0x03,0x6B,"MIPS"'
CELDTPGIF '0x04,0x6B,"MIPS"'
CELDTPGIF '0x05,0x6B,"MIPS"'
mips_backto_mobs

Data Reformatting Requirements

Array Data Desired:

All Arrays

Data Reformatting Option:

Special Instructions:
Each set of 5 DCEs should go in a separate file.

Task Dependencies

Calibration Dependencies

Output and Deliverable Products

Median and minimum ramp starting points for each offset voltage.

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 30 DCEs.
2) Check the stability of the median and minimum ramp starting points and
   see how they compare to the ground data (see the notes below).  Determine
   the offset DAC setting that gives the lowest ramp starting point without
   bringing any pixel to lower than -31000 DN.
3) Determine the relationship between offset voltage and DAC count.
   Ground tests indicate a gain of 1400 DN/DAC count.
4) If the offset values have changed compared to ground values, extract all
   possibly relevant temperature telemetry and seek an explanation for the
   change.  Then assess the expected temperature stability of the influencing
   element and decide whether the DAC setting that was best during this test
   would also be acceptable under the most extreme expected temperature
   conditions.

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

Determine appropriate offset voltages and apply them for use in future campaigns by making changes to irs-mips_pconst_ier.

Failure Modes and Responses

If the starting points of the data ramps do not change as expected in response to offset voltage changes, a careful analysis will be needed to understand the anomalous array behavior. This would be a MIPS timeline stopper. If the starting points are shifted by no more than a few thousand DN relative to ground testing, an anomaly investigation should be performed, but new offsets can be patched and the MIPS IOC timeline can continue. If a larger offset is observed, the ramp starting points likely have a strong temperature dependence on some component of the system, and follow-up observations will be necessary to start producing valid 24um data and to assess the stability of the ramp starting points. If the test fails to execute, other data could be examined to see if the ramp starting points are reasonable, and we could continue with the IOC timeline.

Additional Notes

Additional Notes:

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 observat
ion

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