Cheap thermometer calibration technique?

Water and ice have thermal IR emissivity of around 98%, about as black as things get. So mix crushed ice into cold water in a glass or cup, preferably a thermos, stir, and aim your IR thermometer straignt down into that. Or swish a thermocouple around in it. Even yukky tap water, well stirred with ice, will be within 15 mK of 0C.

The high end, boiling, is a little trickier.

John

I used to 'calibrate' thermocouples by putting them in boiling water.

Graham

Simply apply a millivoltage equivalent to the thermocouple thermometer and see if it reads right (use a known-good DMM with a 200mV range). You'll need to know the ambient temperature accurately. When you short the input it should read the temperature at the jack. When you apply the mV (calculate from desired reading and ambient, given the type-- usually "K" = Chromel-Alumel) it should read that temperature.

The thermocouple itself will either work well enough or not at all, barring the most extreme circumstances.

Best regards, Spehro Pefhany

The classic method, taught to me for checking/calibrating the lab thermometers in HS chemistry class:

Might not have been *PERFECT*, but it was at least reasonably close enough for the stuff we were doing.

And that's normally good enough ! Best ignore the change in boiling point vs atm pressure. ;~)

Graham

IR

compare

A bit of knowledge can be dangerous...

Best regards, Spehro Pefhany

atm

Which is why I reccomended condensing steam on a metal block. Avoids all sorts of problems with superheat. Once you've done that, might as well use the same block in melting ice for consistancy.

On a sunny day (Sat, 15 Nov 2008 14:42:56 +0000) it happened IanM wrote in :

atm

I JUST USED TO HOLD THE SENSOR IN MY HAND AND SET FOR 37.5°C.

Since my HS (and the county it was in) was only about 200 feet above sea level, the error at the high end was generally small enough to be ignored. YMMV if you went to school in Denver... :)

This was high school science, fergawdsake, not the LHC! :)

atm

Got a fever? Hands tend to be pretty cool compared to internal body temperature, more so on some people than others.

You'd do much better by sticking it umm.. somewhere more ummm.. consistent in temperature...

Best regards, Spehro Pefhany

On a sunny day (Sat, 15 Nov 2008 11:24:45 -0500) it happened Spehro Pefhany wrote in :

If you are working a lot then hands are not so cold. Some people always have cold hands ...

Oh, yes, in mouth or up .... But it works very well.

On a sunny day (Sat, 15 Nov 2008 16:19:32 GMT) it happened Rich Grise wrote in :

I AM GLAD YOU ASKED THAT. SIMPLE: CAPS HAVE ONE BIT LESS SET, SO IT SAVES ON ENERGY.

atm

Skin temp is typically significantly lower than actual internal body temp.

When body temp is normal 98.6 F, your hand will be at like 91 F

NO, it does not "save" anything. Particularly energy.

If you published ten GB of data as all caps ASCII text, THEN you MIGHT save a few milliwatts.

Since we merely write a few lines, the amount of energy used is quite large, comparatively, and quite wasteful in all cases where one has only written a few lines.

The less data that a computer actually processes per unit time, the more wasteful they are, and below a certain point, the computer is at an "idle state" from a consumption POV for all tasks performed that are not heavy CPU intensive tasks..

In other words, the GUI and overhead for your machine means that unless you are actually crunching numbers furiously in a process that actually taxes the machine, the little petty bits of "work" you perform all use the same amount of energy per unit of machine time.

In your most comfortable, fuzzy, warm feeling day, your hands are several degrees cooler than your actual body temp. PERIOD.

IR medical thermometers get pointed into the back of your ear canal for a reason. If your hands matched you body in temperature, they would be pointing such instruments at much more accessible locations. They do not.

If boiling point goes up with reduced atmospheric pressure, then why does water boil as one approaches a vacuum at room temp?

Cooking time, not boiling point, goes up. How long would eggs take to cook at room temperature?

Best regards, Spehro Pefhany

LOL !

I've heard that the UK has had as low as 945 mbar during storms. Now, since aircraft barometric altimeters only adjust down to 942 mbar IIRC, that's awfully close to getting a heavy landing or an unwanted float ( mind needs to think which way it would go if it went below 942 local ) unexpectedly. Good thing that commercials have radio altimeters.

Graham

I expect that's simply liberation of dissolved air.

Graham