IR thermometers

The cheap ones are pretty terrible. Not very accurate, and the laser pointer basically lies about the field of view and what it's really pointed at.

Emissivity and ambient reflections can fool even a good IR thermometer, but a pot of soup will have an emissivity near 1 so that's not bad.

A thermally reflective surface reflects the temperature of the ceiling or something, and the IR thermometer doesn't know how to handle that.

That's a cool demo. Didn't know about the emissivity vs reflection details other than the ones that just show a temperature can be very wrong at times. Are liquids in general highly emissive?

Water and ice are almost 100%... almost black at thermal IR wavelengths. Most organics are too.

Aim your IR toy into a bucket of ice and water and see what it says.

Oh, they've been around for a decade or two.

Probably a small black thermistor bead. You can do ratio measure from a resistance, so that's a stingy battery-saving solution; it doesn't take regulated power.

They may not be totally accurate due to surface albedo, but for keeping recipes consistent, they're MUCH more convenient than stick-a-probe systems, and this one

Some of the pistol types are... slow, erratic, and kill batteries soon.

With transparent materials, depth or thickness matter. If it's optically thick enough, it is a black body.

Joe Gwinn

Cheap thin black lawn bags are essentially transparent to thermal IR. To see inside a box, replace one side with the plastic to block convection.

Water has the issue of surface reflectivity depending on the angle as do other substances like plastic. I was attempting to measure the temperature of my freezer and it varied a lot until I realized the plastic packaging would reflect the room temperature and even shiny printed cardboard would do the same thing. I had to point the gadget into a corner behind other packages to get a true reading. The freezer itself is not so reflective.

I sometimes point an IR thermometer at the sky on clear nights. I've seen some pretty low temperatures that are most likely from space with some interference from moisture in the air. One night it was so clear and dry the device didn't give a number. It was something that reminded me of the IEEE floating point format of NaN.

The question was why an IR thermometer could be used to work with a pile of ice or a large pot of soup.

Joe Gwinn

RichD <r snipped-for-privacy@yahoo.com wrote in news:16551ea5-433e-4ba3- snipped-for-privacy@googlegroups.com:

Anything above absolute zero exhibits IR (Planck's Law?)

Transducer accuracy is spot on. The overall device, however consists of a physical optical system getting the target image to the transducer, and then the circuitry that tallies the output and reports it to the user.

Most of the cheap units are fed by a small fresnel front window so the focal 'spot' may be fairly wide and diffuse quickly once past the specified focal length. They are not as accurate as the optical lens fed units, but those have more exact measuring procedure requirements and are typically for longer focal lengths. So the little guys are usually good circuits and a good resistor bolometer transducer and a fresnel and many have a laser pointer.

The fact is that everybody (in industry at least) is now using thermal imagers. When I worked in IR back in the early '80s the first thermal imagers required LN2 bath in a cup behind the sensor and only had like 8 colors and a 480 x 320 array at 4 frames per second and was priced at $35k and came from Japan IIRC. And getting it off onto a VHS tape or onto a 386 was a true pain in the ass.

Most likely a resistor bolometer. Likely a TO-39 package with a

Any of the exotic stuff costs a lost more and the final product would not be the cheap priced ones we see from so many 'players' Klien Tools, Pittsburgh, Milwaukee... etc. A lot of the tool folks have small IR "guns". I bought one at Menard's last week for $12.

It reads 91 on my skin, which is right. And damn! 98.6 on the back of my tongue! I'm sold on its accuracy.