Cheap thermometer calibration technique?



Color isn't the issue. The surface of water is VERY reflective, so any IR the medium generates get reflect BACK into the medium. This is why water has such a poor emissivity.
A matte finish Aluminum block/box filled with a known temp water (circulating) would likely be only a couple tenths of a degree off the water temp, and would allow the IR gun to be calibrated very well.
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On Tue, 08 May 2007 17:39:39 -0700, The Great Attractor

Take a look here for some really good facts:
http://www.mikroninfrared.com/App_Notes/Principles_of_IR.pdf
Water = 0.98
Aluminum varies from 0.04 to 0.3 depending on finish, absolutely useless for IR temperature measurement.
AlwaysWrong.
John
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www.icess.ucsb.edu/modis/EMIS/html/em.html
It shows ice/water having a very high emissivity.
--
Tony Williams.

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On Tue, 08 May 2007 22:42:31 -0700, John Larkin

No, it wouldn't because it is four times more expensive, and it's electrical conductivity and its thermal conductivity are not the same, asswipe.
Alumininum is he right medium conduction wise, AND it is the right medium cost wise. The coating on eother would yield the same result so any point you thought you were making is moot.
You need to get off you "fuck with dark matter" high horse, and get back to reality, boy.
The KeithTard, and the Grisetard can't fuck with me, so what makes you think you can, dipshit?
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On Wed, 09 May 2007 02:23:33 -0700, The Great Attractor

Both are about 2:1 better than aluminum. The factor is even higher compared to common aluminum alloys; hardly anybody wants to machine pure aluminum, and the alloying wrecks both the electrical and thermal conductivity.

You fuck with yourself. Or job is to laugh.
John
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On May 9, 7:56 am, John Larkin [......]

In all metals, the thermal and electrical conductivity track each other quite nicely. Copper alloys such as brass are way less conductive. The atomic clock folks use a copper alloy that is very resistive to make heaters.

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Most pure metals run right around 150,000 k/w per ohm. Brass seems to be higher, something like 250,000.
John
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On Wed, 09 May 2007 07:56:39 -0700, John Larkin

You don't get it. If the surface (read that word carefully, idiot) is prepared correctly, a 0.98 emissivity is achieved, and AL makes an EXCELLENT black body source, and it is used in the industry EVERY DAY.
So fuck off, you goddamned retard.
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On Tue, 08 May 2007 22:42:31 -0700, John Larkin
absolutely the wrong choice though. It is unstable, and gives off vapors, throwing off surface conditions, which is what an imager MUST focus on to get reliable calibration data.
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maybe put it in a black matte metal vessel, (eg a stainless bowl that's been blackened by heat.)
Bye. Jasen
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Both ice and water have IR emissivities of about 0.98... they are already as 'black' as things get. So crushed ice in water, freshly stirred, is a near-perfect 0 degree C IR target in any vessel. A thermos is ideal to keep it very close to 0 C.
John
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Ice mixed with distilled (or for your purposes, tap will be fine) water and allowed to rest for a few minutes will give you 32F within millidegrees. Be sure to stir it every half minute or so to get the thermoclines well distributed.
Boiling water at sea level will give you 212F fairly accurately, less 1F (for your stated accuracy) for every thousand feet of altitude you are above sea level up to a few thousand feet.
Jim

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On Tue, 8 May 2007 09:10:23 -0700, the renowned "RST Engineering

It's possible to get a couple of degrees F error (high) from boiling water, particularly if you use a smooth vessel, such as a glass beaker, to boil the water. Maybe put something like an airstone in the bottom of the vessel.
Best regards, Spehro Pefhany
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On Tue, 8 May 2007 09:10:23 -0700, "RST Engineering \(jw\)"

For the thermocouple, sure. Add some salt even. Not good for the IR tho.

Boiling water is nebulous as one has to decide what "boiling" is, and a hearty boil can well be far above the boiling start point was/is.

Top posting is utterly retarded, boy.
You're a TOFU retard.
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Not sure what you mean by "cheap", but you can get a YSI thermilinear network, which consists of a composite of three thermistors and some precision resistors for about $27. The one that goes from 0-100C claims +/- 0.15C accuracy (+/- 0.27F). That might be expensive for one calibration, but you might use it in the future. Then, you could get a black anodized heat sink with one side smooth, and drill little holes in the side, close to the flat surface, and insert the YSI thermistor and your thermocouple, maybe with some heat sink glop. Then point the IR detector at it. Let it go through some temperature changes slow enough that the whole thing has time to equlibrate, and collect some calibration data for both devices. -- John
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Talk about measuring with a micrometer, marking with chalk, and cutting with an axe!!!
The fellow is looking for a couple of F accuracy.
Jim

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wrote:

True. But this may not be the last temperature measurement he'll ever make. -- John
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Similar to imagery. One should always take the highest resolution shot possible, so that it can be used in any circumstance form a low res paste to a hi res utilization.
Calibrating an instrument should always involve a known source that is of a HIGHER resolution that the instrument itself is.
If a source that equals the instrument's accuracy is used the error level in the two can chain together. In fact, it is termed as "chaining error".
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Pointing at the finned side would yield better emissivity than the "smooth" side would.
Anodized, extruded Al usually has a fairly shiny surface quality.
The ideal black body source is a MATTE finish, so grit blasted Al with some matte black paint (very thin coat) would be best/better.
Yields about a .97 Emissivity. The anodized Al (regardless of color) yields about ten full points lower, if not worse.
Surface quality is a VERY important factor here.
Have a look here for a bit more info. Even though you seem very knowledgeable about it, this should help.
The ideal source, of course, is a cavity.
http://www.mikroninfrared.com/App_Notes/Principles_of_IR.pdf
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On May 8, 6:36 pm, The Great Attractor

I mentioned the flat side because I wanted the sensors to be close to, and so at the same temperature, as the surface. The fins could easily be at a different average temperature.

Thanks for the interesting link. I note that it shows a very common, inexpensive material, black cloth, with an uncommonly high emissivity: 0.98. With this information, I'd change my suggestion to using a flattish copper block (highest possible thermal conductivity) of a size to take up the viewing area of the IR meter, holes and sensors as before, and with a piece of black cloth glued to the surface. I think the whole thing would be inexpensive and fairly accurate. -- John
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