Sedit
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Ultra low thermometer
Iv been working with the recent snow fall trying to reproduce some experiments from a german artical that is discussed here,
http://chemieunterricht.de/dc2/tip/08_98.htm
Problem I am running into is most commercial thermometers only reach a temperature of -40 or so and can't seem to find a quick way to take
measurements of some of the other substances discussed.
I Started with HCl and achieved a temperature of
-41degreesC but to read lower temperatures Im at a loss at the moment as to what use a thermometer that goes as low as -100 might be used for.
Bad part is I wanted to work with this while the snow is still around so ordering one is out of the question for the time being.
Does any one know of a source to find one that can be picked up local for any purpose?
Iv translated the page for anyone interested to a rough over view of,
What is physical-chemical behind it?
You combine a salt in liquid water, causing it to the Wasserdipole by the ions of salt wrapping and so the ionic crystal lattice out.
This procedure is usually endothermic, as the new Ion-dipole interaction is smaller than the lattice energy of salt. The heat of a solution for the
salt is therefore withdrawn from the surrounding area; solution and vessel cool down from (try 1). With sodium nitrate we reach a temperature of -5,3
°C.
You combine with a firm a salt water ice, dissolves the salt to bring even though this is much slower (try 2). Where does the water to solve? You to
know that ice melts under pressure, and therefore under influence of air pressure. That is why ice always with a thin layer of water coated. With this
liquid water is the ice in a dynamic equilibrium.
The water for solving the salt comes from this balance and is constantly being copied. So the equilibrium and ice, slowly disappears. (This effect one
uses by the way to provide in Winter ice on footpath and streets to fight.) In this operation comes to solving the salt is still the melting of ice.
Whose been together with heat of a solution of salt from the surrounding area taken. This also reduces the temperature of the mix ice/salt
characteristics.
Recipes for freezing mixture
In the literature are very many Mischungsangaben to find. But soft information about the composition and reached temperatures in various tables often
widely. In our table will give you some Mischungsbeispiele you can even check. The cheapest is the suitable cooling liquid with salt, at the du -21,3
°C can reach you can (try 3). Instead of mineral salts, you also non-ionic compounds as additions to production of freezing mixture.
This is a translation of the important text on the page and the charts can be found by following the link provided.
Knowledge is useless to useless people...
"I see a lot of patterns in our behavior as a nation that parallel a lot of other historical processes. The fall of Rome, the fall of Germany — the
fall of the ruling country, the people who think they can do whatever they want without anybody else's consent. I've seen this story
before."~Maynard James Keenan
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Lambda-Eyde
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Have you considered using a thermocouple? Sounds to me like you've been using standard glass thermometers.
A common K-type thermocouple would fit your use.
BTW: That's quite an interesting project.  -94*C, that's amazing!
[Edited on 4-3-2009 by Lambda-Eyde]
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Sedit
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Iv thought about the thermocouple but the only one I have at the moment is pyrometer for use in a kiln,this is designed to reach 2500 degrees C, well
away from what I need  . Does any one know how I could rigg one of these up to
test the ultra low temperatures, possibly with an amp prob or something? I have many sitting around that where designed for heaters but I dont think
it would be to much of a stretch to alter there function.
I am quite interested in the fact that they stated Sulfuric acid can reach temperatures of -90 degrees C but when I attemted to reproduce this with
shaved ice I only reached as low as -15C way higher then the HCl reached repeatedly. This is the reason I want to make sure it isnt some kind of
thermometer malfunction and just get something desinged to work at these levels. My problem I have is I was using a cheap ass digital thermometer and
just dont feel these are sufficiantly accurate for such a project.
Knowledge is useless to useless people...
"I see a lot of patterns in our behavior as a nation that parallel a lot of other historical processes. The fall of Rome, the fall of Germany — the
fall of the ruling country, the people who think they can do whatever they want without anybody else's consent. I've seen this story
before."~Maynard James Keenan
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bfesser
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I know they make glass (probably kerosene filled) thermometers that go down to at least -100°C, as I own one. They're not exactly easy to come by
for amateur chemists, but they're out there. Try contacting the eBay seller, papamed4, to see if he currently has any.
If you want a simple way to achieve low temperatures, try dry ice/acetone slush (~-78°C is achievable). Beware of the flammability and volatility of
acetone. Also, it can cause severe tissue damage (frostbite) if it splashes on you. Immerse objects in it slowly, with great care--in my experience
they tend to cause 'boiling' and splashing.
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Sedit
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Im sure they have ones that can gadge that low the problem I am running into is one of time. For future experiments I will definitly get one but
because there is a 'heat wave' comming and I wanted to perform these while there way still 6 inches of snow on the ground because I have found shaved
ice to not reach temperatures any ware near what snow can.
Yes dry ice/acetone is a well documented way of lowering temperature but this is not my goal. My goal is to achieve the temperatures spoke of in the
document I provided. Prelimanary results for the sulfuric acid does not seem to stack up with what is documented.
Knowledge is useless to useless people...
"I see a lot of patterns in our behavior as a nation that parallel a lot of other historical processes. The fall of Rome, the fall of Germany — the
fall of the ruling country, the people who think they can do whatever they want without anybody else's consent. I've seen this story
before."~Maynard James Keenan
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not_important
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alcohol ( 'spirit' ) and toluene are two common liquids used for low temperatures.
http://hbinstrument.thomasnet.com/viewitems/thermometers-spe...
http://www.psawcatalogue.com/low-temperature-thermometers-ps...
http://www.fishersci.com/wps/portal/PRODUCTDETAIL?LBCID=8270...
http://www.microscopes.com/ms-vw-lb-20785.html
some digital ones good to -50
http://www.thermoworks.com/products/low_cost/index.html
the silicon temperature sensing ICs generally are limited to -55 to +150 C
Platinum RTDs are good down to LH2 temperatures, even general purpose ones are useful down to -100C to -200C
http://www.omega.com/rtd.html
http://www.rdfcorp.com/products/surface_rtds/r-stk_01.shtml
And there's nothing wrong with thermocouples, already mentioned, except that you'll want to understand their accuracy and precision in the range of
interest. You may need to do a low temperature calibration, not to the accuracy of true calibration but to check and get within a degree or two. The
freezing/melting point of pure mercury, sublimation temperature of solid CO2, melting point of m-xylene, mp of n-pentane, and boiling point of propane
are all reasonably easy to use.
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chief
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I would use some standart Pt100, Pt500 or Pt1000 thermoresistor. The Pt says: Platinum, and the number says: Resistance at 0 Celsius. This means: A
Pt500 has a resistance of 500 Ohm @ 0 Celsius.
Only thing then necessary: Look up the temperature dependence of platinum-resistance (highly linear above 0, thats why its used), and there you have a
thermometer, that is as good as your ohmmeter.
For temps below 0 Cels. I don't know if it's as good as above 0 ... ; such a thing cost's only a few bucks (5 or 10), and you just can look up the
resistance at any temperature, quite precisely without calibration.
The lowest temp I measured with such a one was -34.5 Cels ; in this range it was OK.
The choice of which one (100, 500 or 1000 Ohm) depends on the accuracy of the ohmmeter ; also through a 1000-Ohm there flows less current, so less
heat introduced by the measuring-current, which might affect the accuracy ... ; therefore also: Only measure for a short moment of time, then shut of
the ohmmeter ... ; this gives precision to maybe 1/100 Degree or more, if the Ohmmeter is accurate enough ...
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Sedit
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Ok that is a damn good idea chief and gives me some also.
What about other metals would they be able to produce the same sort of data?
If fine copper wire of known lenght was wound around something one should be able to use such a thing to predict the temperature of the substance it
was submerged in correct or is the resistance curve not hold at temperatures that low?
Well off to the books fellows because I got some quick getto rigging to learn about 
Knowledge is useless to useless people...
"I see a lot of patterns in our behavior as a nation that parallel a lot of other historical processes. The fall of Rome, the fall of Germany — the
fall of the ruling country, the people who think they can do whatever they want without anybody else's consent. I've seen this story
before."~Maynard James Keenan
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not_important
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Platinum RTDs are the same think Chief was talking about. Nickel and copper can be used, but the higher conductivity of copper makes the resistance
change more difficult to measure.
A problem in DIY RTDs is avoiding putting stress on the resistance element from changing temperature, the strain can cause resistance changes that in
some cases are greater than the changes from temperature. The stress can also lead to breakage of the conductor, especially true when using tungsten
as the resistance element.
Nickel is cheap, but its R vs T curve is quite nonlinear and tends to change as it ages. Copper is distinctly better in that aspect, but requires
long lengths of thin wire, the support and winding of such can be a challenge.
http://www.omega.com/temperature/Z/TheRTD.html
http://www.sensortecinc.com/docs/technical_resources/RTD_The...
http://web.phys.ntu.edu.tw/asc/FunPhysExp/ModernPhys/exp/The...
Omega offers some low cost models, around $20US for better ones, $10US each in 5 packs for some class B units, on down to a 100 pack for $100US for
class B that are rated to -70C but would be usable down to LN2 temperatures with a bit of loss in accuracy.
http://www.omega.com/toc_asp/subsectionSC.asp?subsection=C13...
[Edited on 4-3-2009 by not_important]
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Sedit
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| Quote: | | A problem in DIY RTDs is avoiding putting stress on the resistance element from changing temperature, the strain can cause resistance changes that in
some cases are greater than the changes from temperature. The stress can also lead to breakage of the conductor, especially true when using tungsten
as the resistance element. |
Ok... cool,
Out of curiosity I have some hot surface igniters which are used for lighting gas heaters and they are highly resistance and can handle huge changes
in temperature in very short time frames(something like 0-2500degrees in a matter of seconds). They can also be wired with ease to one of my
multimeters.
At first glance these would seem ideal as a quick DYI low temperature sensor but im not sure if the resistance of one of these temperature probes can
be to high to be useful either. Calibration with a few known temperatures should prove sufficiant as a temperature graph.
Knowledge is useless to useless people...
"I see a lot of patterns in our behavior as a nation that parallel a lot of other historical processes. The fall of Rome, the fall of Germany — the
fall of the ruling country, the people who think they can do whatever they want without anybody else's consent. I've seen this story
before."~Maynard James Keenan
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Formatik
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| Quote: | | Originally posted by Sedit I am quite interested in the fact that they stated Sulfuric acid can reach temperatures of -90 degrees C but when
I attemted to reproduce this with shaved ice I only reached as low as -15C way higher then the HCl reached repeatedly. This is the reason I want to
make sure it isnt some kind of thermometer malfunction and just get something desinged to work at these levels. My problem I have is I was using a
cheap ass digital thermometer and just dont feel these are sufficiantly accurate for such a project. |
I've tried some of those also (in this thread, if you haven't seen it). Although I was more optimistic before, I now highly doubt the last three concerning KOH, H2SO4, MgCl2
since:
1) They fail at producing any references and experimentation for those values.
2) The lowest reported for H2SO4+H2O and snow by all references I've found is about -50ºC. The claimed lowest value referenced I found (not using dry
ice or LN2) was -56ºC using 1 pt 60% HNO3 and 1 pt to 2pts snow or ice.
[Edited on 3-3-2009 by Formatik]
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not_important
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| Quote: | Originally posted by Sedit... I have some hot surface igniters which are used for lighting gas heaters and they are highly resistance and can
handle huge changes in temperature in very short time frames...
At first glance these would seem ideal as a quick DYI low temperature sensor but im not sure if the resistance of one of these temperature probes can
be to high to be useful either. Calibration with a few known temperatures should prove sufficiant as a temperature graph. |
I suspect that they will prove to be too unstable to be useful as measurement devices, as per nickel RTDs, if you are after much accuracy.
Resistances in the 100 ohm to 10 kohm range should be usable; too low and it becomes difficult to measure the changes with temperature, too high and
self-heating & noise pickup can be a problem.
Other problems with DIY are resistance changes in the leads with changing temperature, and thermocouple effects in connections causing errors. They
can partially compensated for with bridge or other 4-wire arrangements, AC excitation with synchronous detection solves the 2nd while reducing
sensitivity to noise pickup (there are high resolution A/D converters that directly support such applications).
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Sedit
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Very nice Formatik, I thank you for that, and im pretty sure that sometime in the near future I will be bringing your threed back to life atlest for a
little while.
I produced lower temperatures using HCl(muratic acid) and ice many many times by first mixing the HCl the snow(nothing else works not even finest of
shaved ice hence the urgency of the experiment) then stiring to a slush which droped the temperature to -37/-38 which is along the lines of what was
posted but after toping it off with more snow it would with ease reach -42 degrees. This would hold below 0 for atlest 3-4 hours slowly raising in the
time in between.
I would like to post more but I cant get any results with out a better thermometer
Knowledge is useless to useless people...
"I see a lot of patterns in our behavior as a nation that parallel a lot of other historical processes. The fall of Rome, the fall of Germany — the
fall of the ruling country, the people who think they can do whatever they want without anybody else's consent. I've seen this story
before."~Maynard James Keenan
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densest
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There are a couple of things you could try:
The high temperature thermocouple has to be a type K (unless it's one containing Pt, which would be too expensive for a ceramic kiln). Type K is good
to -200C according to the CRC. I have seen a type K jack on many very inexpensive digital multimeters ($30 or so, e30? maybe) available for
electricians etc. It will have an error band of about + or - 5C at the extreme ends and +- 1 or 2 C near 0. These thermocouples are quite stable over
time as long as the actual junction is not bent or corroded, so calibrating it once or twice should suffice. The multimeters I saw came with a single
thermocouple.
Iron-constantan (type J) are not recommended for use under 0C because of nonlinearity.
Copper-constantan (type T) have higher output than type K and usually have less error than type K because the alloys are better defined and more
consistent (Cu electrical wire is usually as pure as it can be made without extraordinary cost because its resistance goes up markedly with very small
amounts of impurities, whereas "type K" thermocouples are often made of proprietary alloys which have better mechanical characteristics but slight
differences in output from the standard). The biggest problem with type T is that the copper conducts heat very well which at low temperatures can be
a big heat leak.
Some bimetal thermometers (round dial with a pointer) used in laboratory freezers are reasonably accurate and go below -40 at low cost.
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