Infrared detectors

directional and some parts be very broad (180 degrees even?) or does it all depend on the type of lens you might use?

able to point it "directly" at the stove. (I can get close though).

Where can they be purchased, Jim?

IR remote controls are NIR (near infrared) and operate in the 0.75 µm to 1 µm region. Thermal imagers run between 8 - 15 um. Heat goes on to 1,000 µm. I couldn't find a full data sheet on the TIL100 but if it's undoped silicon, it will only work between about 0.7 and 1.0 µm and will not detect stove heat. (That's why you can see an IR remote control with a digital camera, but not the heat from a stove).

I like the sunlight chopper trick. Veddy clever.

Defensive. In 1980 I got pulled over on I10 at Beaumont by a CHiP who literally pranced up to my car (1977 280Z), and proclaimed, "I've got to hand it to you, every time you saw a black & white you dropped down to the speed limit, so we brought out the airplane" (I was doing about

Once I got back to GenRad I did some experimenting and found that the prop chop was a very narrow range of frequencies, so I made a little magnet mount that I used anytime I was in Californica... they don't (or at least didn't back then) use speed radar. AZ did and still does, but not much enforcement on the open road. ...Jim Thompson

I'm unclear on how that works -- what if the plane never crosses in front of the sun?

Re: stove heat detection, I've seen people mount old Ge transistors at the focus of a flashlight reflector. It might make a pretty sensitive detector if you created a diffamp with one in the reflector and the other behind it, facing the other direction. Not tried personally...

-- john

Correct on the NIR vs. thermal. You can detect thermal radiation in the NIR -- just before you start detecting it with your very own eyeballs. When you see sunlight, flames, incandescent lights, or glowing-hot metal, you are detecting thermal radiation. But that's not what you meant.

Different thermal imagers run in different bands. 8-12um and 3-5um are both popular for imagers operating in the Earth's atmosphere, as those are "windows" with little atmospheric absorption, have useful detector technology, and have manageable optics requirements. Current technology "uncooled" detectors (many of which are temperature controlled at around

I remember seeing an article about 20 years ago about using mm-wave detectors to do thermal imaging -- basically the authors were building phased-array receivers operating at something like 100GHz. The pictures they had of their images were impressive, but I have no idea how practical such imaging would be (other than your antenna arrays would have to be really big -- diffraction is already starting to bite when you're trying to image over kilometers with 3-5um: things just get worse as the wavelength goes up).

The propellors are curved, reflective and twisted. You will probably get flashes of reflected sunlight modulated at the a frequency that is the number of blades multiplied by the rotation frequency, though Jim's scheme might not work on a heavily overcast day. Then again, it might be difficult to persuade the cop plane to take off into heavy overcast.

Exactly. On an overcast or rainy day, the average speed jumped 20MPH ;-) ...Jim Thompson

Ah, the cigarette lighter doubles as a make-up mirror for the ladies. Well, I suppose with some caution, but it isn't exactly a mirror. Oh, and I tend to build my camp fires when the sun isn't shining.

But this does seem like a good product to cut your smoking in half.

The deal with thermal sensing is your hot object is emitting black body radiation, which has long spectrum (spectral?) tails. That is why you can view a soldering iron in with some CCD black and white cameras, even though the CCD is blind beyond a micron.

Color cameras have filters over the CCD elements, and they reduce the detected IR.

Turboprops maintain a steady RPM and vary their prop blade pitch to adjust thrust, so I could see a turboprop having a distinct frequency. Less so for regular piston aircraft.

Prior to LED lighting being used outdoors, I think it would be safe to assume any flickering light faster than a few hundred Hz would be prop reflection. Nowadays it may be more complicated. Even street lights these days are LED based.

Most LEDs are flashed, though the arguments seem endless if DC or flashed LEDs are better. Supposedly the eye detects the peak intensity, so you can PWM the LED for better effective illumination. But I have seen arguments that DC is better.

So, you've never camped out at -40°?

The annoying thing about cigarettes is that they kill so slowly.

The long tail of blackbody radiation is on the long-wavelength side of the curve. The reason you can sometimes see a soldering in the near infrared is because it's so hot, it's almost visible. Some are just visible in the dark.

Hey, fun... Re soldering iron. I've got a little ccd I use to image a ~800nm laser. (So no IR filter.) And a weller soldering iron with the temperature 'programmed' tips. The CCD can't see the 700 F tip. But the 800 F tip stands out clearly. (And my big 200W Weller soldering gun is like a torch!)

George H.

the brain detects peak intensity, the eye average intensity, if it's flashing too fast to see you don't see the peak intensity.

I have an ancient floppy-disk Sony Mavica that can see 1040 nm. If it still works, I'll try it on a soldering iron.

I tested a number of LEDs to answer that. Basically, pulsing mostly just increases i^2*r losses, with few exceptions.

I have camped out at negative degrees..well in C. I use a lighter and have matches as a backup. Contrary to what people say, you can use butane lighters over 10kft. I use a trick I got off the internet. You get the all season Primus stove gas and a Brunton fuel tool to fill the lighter. People call it my crack lighter. It makes quite a stream with the stove gas.

But the tail does go in both directions.

When you say visible, if you aren't talking the tail, then you are talking the peak of the black body radiation. That is mighty hot.

I will admit I don't compute this stuff on a regular basis, but I found a black body calculator.

Plug in 700nm (edge of the visible spectrum). Way more than you need to melt solder.