Contact Stansberry - "; echo " there is a problem w/ your write-up.\n"; return ; } $row = mysql_fetch_array($result); $title = $row["title"]; $princ = $row["principal"]; $deputy= $row["deputy"]; $campn0 = $row["campn0"]; $aorkeys = $row["aorkeys"]; // get real name of principal, deputies $princ = ioc_get_person($princ); $princ = $princ[0]; $deps = explode(",",$deputy); foreach ($deps as $depty) { $depty = trim($depty); $depty = ioc_get_person($depty); $depty = $depty[0]; $depty = explode(",",$depty); $depty = $depty[0]; // last names only $deplist[] = $depty; } $deplist = implode(", ", $deplist); $caid = sprintf("%03d",$caid); $file = "mips-".$caid.$campn.".analysis.php"; // END PHP. ?> <? echo "MIPS-$caid, Campaign $campn IOC/SV Analysis"; ?>

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Task Outcome Summary

Abstract

The goal of this task was to determine the optimal Voffset value for the 24um array. The criteria are to provide the largest possible dynamic range without ever starting any of the data ramps at the bottom rail of the A-D converter. This is accomplished using the preflight nominal Voffset DAC setting of 0x6B.

Analysis

Five RAW mode DCEs were collected at each of 6 Voffset settings. For each DCE, the median and minimum ramp starting points were determined. The results are discussed below, along with a discussion of interesting trends determined from ground data.

Results

The following are the median and minimum starting points for each of the DCEs collected in the task MIPS-125. In the first DCE of each observation, the first two frames are zeros, the third frame generally has a pedestal offset, and the data ramps under these dark conditions have negative slopes. As a consequence, the most negative frame was the 8th and final frame of the 4s DCE. For all other DCEs, there is no pedestal offset and the slopes are always positive. 
Filename                                    median   minimum    frame  Voffset
MIPS.1.0006758144.0000.0000.01.mipl.fits    -28120   -30126       3     0x6B
                                            -28496   -31011       8     0x6B
MIPS.1.0006758144.0000.0001.01.mipl.fits    -28116   -30087       1     0x6B
MIPS.1.0006758144.0000.0002.01.mipl.fits    -28122   -30131       1     0x6B
MIPS.1.0006758144.0000.0003.01.mipl.fits    -28122   -30185       1     0x6B
MIPS.1.0006758144.0000.0004.01.mipl.fits    -28127   -30146       1     0x6B

MIPS.1.0006758144.0001.0000.01.mipl.fits    -29512   -31504       3     0x6A
                                            -29894   -32413       8     0x6A
MIPS.1.0006758144.0001.0001.01.mipl.fits    -29505   -31505       1     0x6A
MIPS.1.0006758144.0001.0002.01.mipl.fits    -29507   -31518       1     0x6A
MIPS.1.0006758144.0001.0003.01.mipl.fits    -29508   -31542       1     0x6A
MIPS.1.0006758144.0001.0004.01.mipl.fits    -29511   -31496       1     0x6A

MIPS.1.0006758144.0002.0000.01.mipl.fits    -30902   -32768(1pix) 3     0x69
                                            -31291   -32768(4pix) 8     0x69
MIPS.1.0006758144.0002.0001.01.mipl.fits    -30901   -32768(2pix) 1     0x69
MIPS.1.0006758144.0002.0002.01.mipl.fits    -30906   -32768(2pix) 1     0x69
MIPS.1.0006758144.0002.0003.01.mipl.fits    -30909   -32768(1pix) 1     0x69
MIPS.1.0006758144.0002.0004.01.mipl.fits    -30910   -32768(1pix) 1     0x69
(Note that the same few pixels ([79,127] in all cases, [63,127], [64,127], and 
[87,127] once or twice each) were off-scale in all cases.  These pixels
lie on the top row of the 24um array.)

MIPS.1.0006758144.0003.0000.01.mipl.fits    -32278   -32768(24%)  3     0x68
                                            -32681   -32768(43%)  8     0x68
MIPS.1.0006758144.0003.0001.01.mipl.fits    -32274   -32768(24%)  1     0x68
MIPS.1.0006758144.0003.0002.01.mipl.fits    -32275   -32768(24%)  1     0x68
MIPS.1.0006758144.0003.0003.01.mipl.fits    -32282   -32768(25%)  1     0x68
MIPS.1.0006758144.0003.0004.01.mipl.fits    -32279   -32768(25%)  1     0x68

MIPS.1.0006758144.0004.0000.01.mipl.fits    -26724   -28741       3     0x6C
                                            -27115   -29615       8     0x6C
MIPS.1.0006758144.0004.0001.01.mipl.fits    -26717   -28781       1     0x6C
MIPS.1.0006758144.0004.0002.01.mipl.fits    -26724   -28772       1     0x6C
MIPS.1.0006758144.0004.0003.01.mipl.fits    -26723   -28775       1     0x6C
MIPS.1.0006758144.0004.0004.01.mipl.fits    -26724   -28777       1     0x6C

MIPS.1.0006758144.0005.0000.01.mipl.fits    -25307   -27344       3     0x6D
                                            -25698   -28240       8     0x6D
MIPS.1.0006758144.0005.0001.01.mipl.fits    -25301   -27372       1     0x6D
MIPS.1.0006758144.0005.0002.01.mipl.fits    -25306   -27400       1     0x6D
MIPS.1.0006758144.0005.0003.01.mipl.fits    -25306   -27396       1     0x6D
MIPS.1.0006758144.0005.0004.01.mipl.fits    -25307   -27402       1     0x6D


Average of the median and minimum starting points for DCEs 1-4:
    Starting Point      Voffset   Offset from 0x6B    Gain (DN/DAC)
    med     min
  -28122  -30137          0x6B             0                --
  -29508  -31515          0x6A         -1386              -1386
  -30907  -32768          0x69         -2785              -1392
  -32278  -32768          0x68         -4156              -1385
  -26722  -28776          0x6C          1400              -1400
  -25305  -27392          0x6D          2817              -1408

The following values were measured from task MIPS-990 in campaign C,
when the array was subjected to extremely bright light conditions.
MIPS.1.0006653440.0000.0000.01.mipl.fits    -30087   -31905       3     0x6B
MIPS.1.0006653440.0000.0001.01.mipl.fits    -30391   -32177       1     0x6B
MIPS.1.0006653440.0000.0002.01.mipl.fits    -30433   -32217       1     0x6B
MIPS.1.0006653440.0000.0003.01.mipl.fits    -30447   -32251       1     0x6B
MIPS.1.0006653440.0000.0004.01.mipl.fits    -30455   -32225       1     0x6B
MIPS.1.0006653440.0000.0005.01.mipl.fits    -30459   -32225       1     0x6B
MIPS.1.0006653440.0000.0006.01.mipl.fits    -30463   -32260       1     0x6B
MIPS.1.0006653440.0000.0007.01.mipl.fits    -30465   -32246       1     0x6B
MIPS.1.0006653440.0000.0008.01.mipl.fits    -30466   -32241       1     0x6B
MIPS.1.0006653440.0000.0009.01.mipl.fits    -30469   -32243       1     0x6B
The mean gain is -1394 +/- 9 DN/DAC. In ground testing, the gain was determined to be roughly -1400 DN/DAC count, fully consistent with this measurement. The median starting point for Voffset = 0x6B and CE-1 was -27972 DN. Ground measurements indicated a drift in ramp starting points of up to 100-200 DN in 12 hours. There also was some evidence in ground testing that the median starting points were a few hundred counts lower when the array was being exposed to bright light. The extreme light conditions present during campaign C caused an offset of roughly 2300 DN. We will never experience such extreme light conditions during science operations, but this clearly demonstrates that the light-dependent offset is real and that we need to allow for perhaps as much as 500 DN of offset in bright light conditions. As long as we leave the ignore_frames parameters at 1, this bright-light offset is unlikely to cause problems since we start our slope-fitting after 0.5s of light exposure. Ground testing also indicates that the starting points of the data ramps are dependent on the CE temperature, with a gain of -(15-20) DN/degree. The CE Box temperature during MIPS-125 was 10.6 +/- 0.1 C, about 2 degrees cooler than the box temperatures during the ground test. These environmental dependences dictate that the minimum ramp starting point not be set any lower than -32000 and preferably not lower than -31000 DN.

Conclusions

The first DCE poses the biggest risk of a data ramp starting below the bottom rail of the A-D converter. There is a pedestal offset when the reset is released, and it has an amplitude of order 1000 DN for some pixels. Combined with the recommendation above that the minimum starting point for a data ramp not be set any lower than -31000, this indicates that the current Voffset DAC setting of 0x6B is acceptable and that we would not want to set the starting points of the data ramps any lower. There is some possibility of 1-2 pixels on the top row of the array being off-scale on the first read after the reset/read frame in the first DCE of an observation.

Output and Deliverable Products

None

Actions Following Analysis

My recommendation is to use a Voffset DAC setting of 0x6B. This is the preflight nominal setting, so no action is required. Since this offset voltage does not leave much margin, we need to be vigilant to make sure that the ramp starting points do not drift extensively over time or under extreme light conditions, else we could get invalid data.