thermal imagers

On a sunny day (Sun, 15 Jan 2012 08:53:35 -0800) it happened John Larkin wrote in :

No, 'camera obscura' should also work for IR.

Except that the cardboard is also incandescent in the IR, unlike the visible. "Camera obscura" means "dark room", and there ain't no such animal in the thermal IR, unless you use your cryocooler!

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058

hobbs at electrooptical dot net
http://electrooptical.net

The other reason it does not work is because an IR thermometer is calibrated for the entire fov. If you obscure it, you can only go down to the detection limit, such as "a one inch spot on a ten inch circle at ten feet away" (or whatever yields say a 1 degree fov), and even then, the actually heat source target has to be right behind the aperture. If you concatenate the target down below that "one inch spot", the same temperature will not register the same energy in the instrument and an errant reading will result.

One degree is a serious IR thermometer. The cheap ones are more like

30 degrees, fine for measuring the average temperature of a wall. Some have laser pointers, which is downright deceptive.

That's why the imagers are so much better.

John

I was searching for that !!!!!!!!

Greg

I just wanted to mention, the laser model I use goes out of calibration if you take it outside in the cold. It slowly cools down and becomes useless measuring actual temperature.

Greg

film.

Anyway, it worked for me. I forget the exact configuration, but there were some opamps that got uncomfortably warm to the touch. I think I actually used a tube, now that I think about it.

Greg

The particular fluke model I use, regardless of the number of degrees, which I'm not sure of the spec, but the hot spot is easy to show intersection from a few feet away within a couple inches. The near field I used for the board was a little HF button model.

Greg

film.

Then you'll measure mostly the temperature of the wall of the tube. There's a reason people pay $1000 for a germanium lens.

John

On a sunny day (Sun, 15 Jan 2012 14:28:36 -0500) it happened Phil Hobbs wrote in :

Sure, you are right. But is not this temperature difference way above thermal background? I mean if you look at a component 30°C above ambient?

Seems a lot cheaper than a geranium plant lens... Sort of like the idea.

John Larkin:

You are wrong, Jim is right, he just published a beautiful design. :-)

If you hold the camera and cardboard still, and wave the board around in front of it till you get the largest signal, you've found the hot spot. Of course you can do the same with your upper lip or the back of your hand.

The sensitivity of a pinhole camera goes down as the projected solid angle of the source, so if your hole subtends 1 degree out of a 30 degree FOV, your sensitivity goes down by a factor of

(sin(1 deg)/sin(30 deg))**2 = 0.0012.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058

hobbs at electrooptical dot net
http://electrooptical.net

And it only took him a week to do it!

John

Greg,

From memory...I was searching Harbor Freight for a Nail Locator [not a stud finder] and the same page that showed an electronic 5 in 1 product from CenTec showed a section of 'what others bought who bought this' or such

I 'think' one item was a thermal imager and the price was incredible. Somewhere also listed was a miniature fibre optic camera with some 6 to 8 foot run-length.at incredible price, too.

So, check Harbor Freight.

On a sunny day (Mon, 16 Jan 2012 10:30:31 -0500) it happened Phil Hobbs wrote in :

Yes that does not leave much now does it....

On a sunny day (Mon, 16 Jan 2012 07:48:39 -0800) it happened John Larkin wrote in :

But Jim has other things top do, he is working on a chip IIRC.