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

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

An IR thermometer will not be very accurate on lower as body temps due to the radiation measured.

An IR is good for above 50 F or 25 C Calibration is best done close to the temps really measured. And yes boiling and freezing water is very accurate and the method with the black body is best.

I noticed that my typical Fluke IR thermometer only works at room temperature. I took it outside last winter, and after the unit starts to cool, forget it.

greg

Have I got really rubbish thermometers? I've tried measuring body temperature both in my mouth and under my arm, and it's never more than about 30C.

both in my mouth and under my arm, and it's never more than about 30C.

I never thought that I would ever get to say this to anyone and really mean it.

STICK IT UP YER ASS! :-] Hehehehe!

both in my mouth and under my arm, and it's never more than about 30C.

And if next time I forgot I'd done that, and stuck it in my mouth?

Have you ever heard the term, "wash"? And a healthy ass shouldn't have anything harmful in it - it's inside your own body, right?

I think you could survive your own fecal remnant attack. Sheesh. Wash it off already!

But some parts of the body aren't supposed to come into contact with other parts.

Try feeding the exhaust pipe into the air intake in your car and see if you can drive it a fair distance.

drive it a fair distance.

Bannana in the tailpipe fails as well...

Bwuahahahaha!

Probably. I just tried a couple of inexpensive IR thermometers, and both read between 36 and 37 degrees C while looking into my mouth. Sounds about right (though I'm not about to check it using a bare thermocouple).

Dave

Was it inaccurate only while cooling down, or did it remain inaccurate once fully cooled to outside temperature? The sensor's own temperature matters, and there should be a thermistor or something to measure the sensor temperature and compensate for it, but this can be screwed up if temperature is changing rapidly.

Dave

can drive it a fair distance.

Not as much backpressure as a spud.

Never had the use of an IR one.

... Well, it is true that you can't touch your ear with your elbow; are you talking about the "naughty bits"? That's just the body shame that got programmed into you by strict religious parents.

This makes no sense whatsoever.

Cheers! Rich

can drive it a fair distance.

That should have said "Try to feed the exhaust pipe into the passenger compartment, and see if you can drive it a fair distance."

Hehehehehhee! Reminds me of Slaughterhouse Five...

My parents aren't religious, luckily. Or I'd have been thrown out of home for making fun probably.

Are you seriously suggesting that excrement is safe to eat?

Those two lines together made me laugh. It reminded me of a drunk person.

My point was the exhaust is not compatible with the air intake. It would choke. Same as if you inhaled farts.

can drive it a fair distance.

Am I allowed to use scuba gear?