🚀 go-pugleaf

On Tue, 07 Aug 2012 19:34:24 -0700, josephkk
<joseph_barrett@sbcglobal.net> wrote:

>On Tue, 07 Aug 2012 14:04:19 -0700, Jon Kirwan <jonk@infinitefactors.org>
>wrote:
>
>>On Tue, 7 Aug 2012 12:42:56 -0700 (PDT), George Herold
>><gherold@teachspin.com> wrote:
>>
>>>On Aug 7, 3:19 pm, Jon Kirwan <j...@infinitefactors.org> wrote:
>>>> On Tue, 7 Aug 2012 05:23:52 -0700 (PDT), dp <d...@tgi-sci.com>
>>>> wrote:
>>>>
>>>>
>>>>
>>>>
>>>>
>>>> >On Aug 7, 5:11 am, Jon Kirwan <j...@infinitefactors.org> wrote:
>>>> >> ...(Most of my work was in the
>>>> >> visible, near UV, and near IR -- but for very different
>>>> >> applications.) I still have some decent setups here and I've
>>>> >> designed some devices that can be made for only a few
>>>> >> dollars, and wavelength calibrated for $8 more, so that high
>>>> >> school students could actually built their own real-world
>>>> >> equipment that could genuinely "do science" and meet
>>>> >> calibration standards. No intensity calibration, though,
>>>> >> sadly. That costs money to do. (Unless you have a suggestion
>>>> >> about how to do it on the cheap?)
>>>>
>>>> >Oh no, I could not possibly have a suggestion. My spectrometers
>>>> >don't seem to have an overlapping wavelength range with yours,
>>>> >mine are xray/gamma. I am practically clueless when it comes to
>>>> >those in the UV and below range, mine generally count single
>>>> >photons.
>>>>
>>>> For all those reasons, that is why I would LOVE to see the
>>>> "optics" (and the schematics, as well.) Totally new area for
>>>> me to learn about. In my region, it's all about electron
>>>> transitions -- and no molecular dissassociation.
>>>>
>>>> I'd expect you'd count single photons at those energies --
>>>> just one probably creates quite a shower to deal with. I'd
>>>> like to know, in practice, how one measures the energy.
>>>>
>>>> Also, in space there is a serious problem with "brown crud",
>>>> which is smashed, charged particles that come from the
>>>> satellite's own fabrication scattered into space, which
>>>> because it is charged comes back to the spacecraft at some
>>>> later time, but sticks elsewhere (not where you want it.) I
>>>> don't know if there is a problem with this on Mars -- there
>>>> is an atmosphere of sorts. But I'm curious just the same if
>>>> there is an accumulation problem and how it is dealt with.
>>>>
>>>> >Efficiency calibration is costly on those for gamma, too,
>>>> >though - the calibration source costs thousands. The rest, hm,
>>>> >has become much less expensive since the release of the
>>>> >netmca-3 (one can still spend tens of thousands on it but
>>>> >does not have to any longer).
>>>>
>>>> Now THAT I totally believe. I probably couldn't afford it.
>>>> But I still could learn.
>>>>
>>>> >I would be curious what gamma spectrometry the thing is
>>>> >carrying on board, too (if any, but likely so). Unlikely
>>>> >HPGe, but then who knows, Mars is a cold place, they may
>>>> >have figured some practical way to cool things down to
>>>> >about liquid nitrogen.
>>>>
>>>> Well, they certainly don't have much atmospheric pressure to
>>>> worry about.
>>>>
>>>> Which reminds me of another thing. How do they convect the
>>>> internally generated heat away. I recall hearing about
>>>> multiple power systems, operating around 32V at near 2A. More
>>>> than one. This power must be convected/conducted away -- no
>>>> way they want to radiate it. I wonder if they push it
>>>> (costing more heat) towards a vane or arm and drag it around
>>>> on the surface to get rid of it?
>>>
>>>The atmosphere won't help much.
>>>
>>>Why not?  Thermal conductivity of air is pretty much constant till you
>>>get below 1 Torr or so.  Wiki says the mean pressure on mars is about
>>>0.1 psi, which is ~5 torr.
>>
>>Good point.
>>
>>What triggered my comment is remembering that heat buildup
>>was most certainly a problem during broadcasts with the high
>>gain antenna system towards Earth. They can't operate it
>>continuously, if I recall correctly. Made me wonder about the
>>rest. I had also remembered the case of satellites and "knew"
>>that the Martian atmosphere could be as little as a few tens
>>of Pascals. So I projected that heat accumulation may be a
>>problem. Apparently, it isn't.
>>
>>I gather your point. To understand it more fully, I need to
>>think more closely about mean-free-path, I guess. Thanks.
>>
>>>Re spectrometer calibration:  We had this "black body" source. (from
>>>Ortec?)  That could be used for intensity calibration.  PITA though.
>>
>>The problem for students is that they cannot afford the $800
>>it takes to get a $8 tungsten bulb calibrated. (It can cost a
>>lot more than that, too.) Then they need to set up a careful
>>station for making the calibration. It's just plain too
>>expensive to do. And I don't know a way around it. Wavelength
>>calibration is CHEAP!! $12 buys a merc-argon calibration
>>lamp, which fires up with the Argon first (for about a minute
>>or two where you get some very nice Argon lines in the longer
>>wavelengths) and then the Mercury kicks in and dominates with
>>it's lines. A couple of well-timed snapshots and you've got
>>enough (with software) to completely calibrate your pixel
>>positions in a cheap ($10) megapixel camera.
>>
>>I'd LOVE to figure out a cheap intensity calibration setup,
>>though. So would a lot of other people, I suppose.
>>
>>>But maybe you could do something on the cheap with a tungsten light
>>>bulb.
>>
>>But that's the problem. I can get a cheap tungsten lamp. They
>>are VERY CHEAP. In fact, the EXACT SAME ONE I would buy,
>>calibrated, is dirt cheap uncalibrated. It is the calibration
>>data that comes with a newly calibrated lamp that costs so
>>darned much. It needs to be traceable to standards. And you
>>pay for that. Plus, you need an expensive power supply to
>>operate it (0.1% current control is standard.) And it ages,
>>too. Within 100 hours or so, it's drifted enough that it
>>needs recalibration.
>>
>>Thanks,
>>Jon
>
>It may be possible to start with a selection of calibrated LED sources
>(kind of like the near IR ones used for light source & light meter used
>for fiber optic cable measurements).  With a nice selection of say a dozen
>wavelengths in the range of interest, it may become reasonably feasible.
>With a decent calibration cycle as well.
>
>Internet patent dated 7 August, 2012, all rights reserved.

I know you were laughing. Don't. I've been there. I've
already built calibration LEDs. Not for the purpose of
calibrating visible wavelength spectrophotometers, though.
They were very special-purpose standard-candle devices
because dispersion isn't anything like a tungsten lamp and
alignment of the LED die severely limits practical use.

If you had ANY idea just how HARD it is to calibrate LEDs for
optical output....

First, you buy 1000 LEDs and request that they all come from
the same FAB and batch. They will need to be operated at an
elevated, controlled temperature when they are finally used,
so you set each one up to run at that temperature and then
continuously observe them for 200 hours of operation. In that
time, most of them will drift all over the place and will NOT
settle down entirely in that time. You throw those away.
Others will not drift all over but will drift way too fast to
be any good. Throw those away, too. Of the 10 or 15 LEDs left
in the batch that happen to have stabilized well enough in
200 hours of operation to appear to be useful, you go through
the trouble of cutting away the epoxy with precision tools
and then operating them some more while producing a
calibration table for each in their final module.

It's not cheap. Their wavelength skirts are wide, too. Now do
this for a variety of visible areas to produce what you are
talking about?

Tungsten gives nice coverage. Here's a calibration table I
got from Optronix for a 45W tungsten lamp (actually a 50W),
model 245M, using a standard distance away using a standard
optical arrangement. Filament must be vertical, current
controlled to 0.1%, etc. It gives an example of how many
points are sometimes used, though you can always pay for
more. Given the black body curve behavior, interpolation at
different points is manageable.

250,.000249
270,.00818
290,.00217
300,.00332
310,.00489
320,.00697
330,.00960
340,.0130
350,.0173
370,.0285
400,.0531
450,.118
500,.212
555,.337
600,.446
654.6,.574
700,.669
800,.830
900,.902
1050,.892
1100,.865

Jon