Update: Position of Temperature Sensors

We installed the new temperature sensor cable and discovered that the previous cable was installed backwards with respect to the wire drawings.  This means the temperatures that were originally designated as "C"s are now correctly identified as "D"s and vice versa.  Below is a schematic of the correct configuration for the current temp sensors on EXES.

 

Motor cable and noise

We're in the process of reworking the motor cable to a) make it long enough for flight and b) remove the twelve Lemo connectors for easier integration.

As part of this, Dave Black has kindly built a protoype for the new cable design, so that we can make sure we don't create any new noise vulnerabilities when we remove the Lemos. The Lemos have the characteristic of keeping the cable shield continuous from the CWR to the forward-plate area, and maintain a faraday-like enclosure right the way through. This is likely not important, since the shield is broken at the motor location and there is already ample opportunity for the motor wires to contaminate the signals coming back from the pots or the array cabling.

Still, it seemed worth checking. Jeff and I compared scope measurements at equivalent points on the existing and the prototype pot-sensing cables and found no difference, so I've asked Dave to fab the new cable to match the prototype.

The new thing learned in the course of this (and the reason for posting here) is that we see <2mV rms noise on the scope from the pot cable with everything switched off, and not much more as we switch on CWR components until we power up the (switching) power supply for the Cal Source blackbody. This PS puts a lot of hash on the line and raises the noise to ~12 mVrms as indicated on the scope. Enabling the motors is still the dominant source (~35 mVrms), but I hadn't realized how noisy the Cal source power supply is.

Whether the Cal Source PS noise actually couples in to our FITS data remains to be tested, but we should look into that at our next opportunity since we don't have a workaround for it in place....we can switch it off at the Pulizzi via software, but I don't know whether that would leave us with a useful cal source blackbody given stabilization times. I need to check with Bob as to what his latest noise numbers are and how best to acquire comparable data with the PS switched off.

Emissivity of the KRS5 Window in CD014

The purpose of this experiment was to find how much light is being emitted by the window lens.
The data is from CD014, when the irradiated detector was first installed at a tilt.

Brief excerpt from the log book is below.

; Lab Book V, pp27

; Spectra at 10.2, 13.5 and 24um, looking at room, 77K sponge, mirror

; High-medium mode, slit5 crossed with decker dash #2

; 4 1 egos or 6 1 egos, 33 ctdelay

; 

; BP14100, echelleV~8.5V

; file5 6 1 egos, 33 ctdelay, slit mirror

; file6 6 1 egos, 33 ctdelay, room

; file7 6 1 egos, 33 ctdelay, LN2 sponge

; 

; OCLI Q, echelleV=8.0998V

; file8 4 1 egos, 33 ctdelay, room

; file9 4 1 egos, 33 ctdelay, LN2 sponge

; file13 4 1 egos, 33 ctdelay, slit mirror

; 

;  Soifer, echelleV=7.7380

;  file10 6 1 egos, 33 ctdelay, room

;  file11 6 1 egos, 33 ctdelay, LN2 sponge

;  file12 6 1 egos, 33 ctdelay, slit mirror

We took hi-res spectra at three wavelength settings: OCLI Q at 10.2um, BP14100 at 13.5um and Soifer at 24um. 

We took spectra looking at the 295K room, a dark frame (using the slit wheel mirror), and of a piece of sponge in front of the window which has just been submerged in LN2 for 30s.

Here is what the room spectra looked like for the different filters.

BP14100, 13.5um

OCLI Q, 10.2um

Soifer, 24um

Labeling each: 

spec_room

spec_ln2

spec_dark

The flux from the room+window would be spec_room-spec_dark.

The flux from the window alone would be, approximately, spec_ln2-spec_dark, where we expect the cold foam to produce almost no contribution in comparison to the light from the room, leaving the main contribution from the window.

First I selected pixels which were illuminated - DN > 500. At the high echelle angle of the BP14100 spectrum, I took care to avoid pixels that were contaminated by the gleam, caused by misalignment on the grating. These images show the pixels used in the fractional contribution calculation.

Soifer: Illuminated, non-contaminated pixels for used for calculation below.

OCLI Q: Illuminated, non-contaminated pixels for used for calculation below.

BP14100: Illuminated, non-contaminated pixels for used for calculation below.

Then, for these illuminated pixels I divided the window-only spectrum by the total room+window spectrum, i.e.

frac=(spec_ln2)/(spec_room)

Here are the histograms of the fractional contribution pixel values. The median value of the fractional contribution is printed on the histogram plot.

BP14100, near 13.5um

OCLI Q, near 10.2um

Soifer Filter, near 24um

So, in summary, the window seems to contribute:

2.1% at 10.2um

0.7% at 13.5um

2.7% at 24um.

I'm not sure whether this is the "emissivity" as it is usually defined. Would appreciate feedback. All data, as well as a idl "journal file" for loading and producing the histograms above, are uploaded to the Dropbox.

For those with access: EE/analysis/CD14/emissivity/

Linearity Correction

Using the notes from Bill Vaca, I re-examined correcting for the non-linearity in the detector.  The results show that this method corrects for the non-linearity quite well.  Below is an explanation of the processes used for the correction.

As discussed in the email from Bill Vaca, we want the counts to follow a linear path with time:
Dn = c*t, where c is a constant
But what we see for NIR detectors is something more like:
DN = a0 + a1*t + a2*t^2 + ...

We would like to have a correction for non-linearity that is independent of time, so instead of looking at counts, we will look at the rate, r (Dn/t) versus DN.
So again, we want:
r_ideal = Dn/t = c
But we observe:
r_obs = b0 + b1*Dn + b2*DN^2 + ...

To obtain a correction factor for EACH pixel we can use:
DN_corr = r_ideal/r_obs = 1/(b0/c + (b1*DN)/c + (b2*DN^2)/c + ...)

Next you must figure out what to use for the constant, c.  One choice would be b0, but as Bill pointed out, at small DN, the observed rate can actually drop.  I tried to use b0 and found that sometimes it caused the correction to fail (i.e., results would not be linear).  So I tried Bill's other suggestion, where you find the maximum value for the rate, r_max, as determined by the polynomial, r_obs.  This approach appears to be much more robust and is what I have adopted in my code.

Now the correction value is computed at each pixel in terms of DN as:
DN_corr  =  1/(b0/r_max + (b1*DN)/r_max + (b2*DN^2)/r_max)


I have adopted using a second order polynomial for several reasons.  1) Using a 4th order would sometimes cause pixels to be over-corrected and 2) the fits for images with only 4 reads (such as 100 1 egos) would often fail when a 4th order polynomial was used.  I believe that for images with more that 4 reads, a 4th order typical gives a better fit than a 2nd order (but not by much, this is something I should quantity), but for now I am using a 2nd order polynomial for all images.  The polynomial is only fit to pixels below saturation.  Right now that value is hard coded in, but could easily become a variable that changes with bias, etc...

Below is a plot that shows the correction for a 5X5 pixel area in a 25 1 egos image (N2 S0 N3 S0 N3 S0 N1 D0).  I have also examined 100 1 egos images and the correction still works very well.

There are still some issues dealing with "bad" pixels or pixels that have negligible flux levels.  I either try to ignore these pixels, since I will not obtain a meaningful fit, or they are fit, but typically are over corrected.  Since these are the pixels where we will not be using to make measurements, I do not see it as too much of a problem, but will try to come up with a more robust way of dealing with these "bad" pixels at a later time.  Any suggestions are welcomed.
 

Pupil Image Sharpness and aperture size

During CD16, we serendipitously noticed that the pupil images are sharper when the aperture is opened  up. 

When we take pupil images, we typically must use a short wavelength filter while crossing a slit with a decker dash, cutting down on light. Slit5 x 14pix decker dash is typical. 

Here is a what we got with the ZnSe pupil lens, filter=N04679, slit5 x 14 pix decker during cool down 16. The second image is a 

version that's blown up and rotated by 22.5 deg, so that the two parallel wires line up with columns and the single target wire lines up along rows. The FWHM of the pupil target wires was 15-20pix. 

Then we saw marked improvement in the sharpness of the pupil target when we used the middle of the central decker arc crossed with slit 5. 

The FWHM of the two parallel target wires became 7.8pix. The FWHM of the single target wire perpendicular to the wire pair was still around FWHM ~25 pix.

The explanation is that when the aperture is widened, we use more of the pupil lens diameter, which collapses the depth of focus. (If I got that wrong, please correct me). 

I'm not sure if we expect a focus difference for the differently oriented wires due to the aperture asymmetry, but that will be clarified experimentally in our next cold cycle, when we a newly acquired 10% ND filter will allow us to take pupil images with the full circular aperture.  

 

EXES Development Calendar

Test sharing the Schedule from Sybil for DAOF software testing.
If you don't see anything below, try clicking this and tell me if you can see anything. Calendar

Pupil Lens Location

The purpose of this test was to ascertain the best position of the ZnSe lens in the lens wheel.  This test was conducted warm using the red laser and the cold stop wires.  The data can be found in directory /data/Warm017/warm017_2013dec/20/.  The position of the lens was measured from the top of the lens teflon ring to the top of the lens barrel (Delta z, see Figure 1).

Figure 1.

As the position of the lens was moved, the magnification of the pupil image changed.  To account for this difference, the diameter of the pupil was measured for each image and the FWHM was scaled accordingly.  The FWHM was estimated by measuring the FWHM of the two parallel cold stop wires using a 1D gaussian fit.  The two wire values were then averaged to obtain the final value to each pupil image.  The error was estimated solely by repeating the diameter and FWHM measurements 5 times for each pupil image and so should be taken as a lower limit since there are many other possible sources of error.  Figure 2 shows how the FWHM changes with pupil lens location.  From this experiment I do not believe it is possible to conclude that one position in the lens barrel is significantly better than the others and so it may be best to place the lens in the previous cool down location.

Figure 2.

Pre-Ship Top Five

Folks,

Based on notes and discussions around the Pre-Ship review, here are Top Five Tasks in various areas prior to Pre-Ship. We'll be burning these down and other tasks will no doubt come up. For now, I'd appreciate your taking a peek and filling in things you think should make the list. Thanks.

Software:

- Establish working relationship with Sybil and the TOs, run through Tier 3 with them.
- Develop Tier 4 test plan (w/Sybil and Liz concurrence) and run against DAOF SIL (is this possible pre-ship??)
- Test AORs from SPOT and refine as necessary.
- Tweaks to LabView Command server to get cal source working efficiently.
- Configure 2d Mac Mini for QLook software, simulate full-up observation.


Hardware:

- Complete cable fab (housekeeping, eBox power, paraboloid, motor/pots) and labelling.
- Inspect internal fasteners and fix any sketchy bits (make spares for cam/coll adjusters)
- Flight assembly with NAS fastener swaps complete.
- Test complete vent/pressure relief system.
- Detector operating point and ground scheme selection.


Logistics:

- Arrange for trucking of non-SI equipment.
- Outfit traveling lab cabinets/spares.
- Arrange for air-ride truck for EXES, and confirm lifting plan for SI.
- Verify access/flight paperwork status for EXES team @ DAOF.
- Detailed travel schedule and staffing plan for Commissioning I.


Docs/certs:

- Resolution of weld waiver, neck sizing issues.
- Completion of ICD/SI System Spec verification.
- Completion of DAOF procedure development, traveler.
- Confirm DAOF certs for PRDS, lifting hardware.
- Confirm DAOF LDEM signoff on critical lift plan