🚀 go-pugleaf

On Tue, 07 Aug 2012 20:36:55 -0700, Jon Kirwan <jonk@infinitefactors.org>
wrote:

>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 wasn't.  I thought it was an idea worth investigating, not necessarily
the right approach to a solution.

>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....

That is why it is just a suggestion for a maybe workable approach.
>
>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.

Agreed.  I have hit the drift wall a few times myself.  Not fun.

>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.

Yep i was worried that it could be this bad.
>
>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

Yep i have fought those curves as well.  Tiresome but doable.  You get the
same kinds of thing is radiation dosing semiconductors (bipolar
transistors mostly, measurements interest included 1/ H(fe), I(cbo), and a
couple of others).  Also combined radiation (includes annealing effect
between the radiation types gamma vs neutron).

?-)