Thought a brake was hanging up. Got out, and dig the laser aimed
IR thermometer out of my tool box. Go around and check the temps
of the brakes, to find the one running hot.
Other use -- read a thermostat on top of the motor. Find what
temp the thermostat maintains.
Christopher A. Young
You can\'t shout down a troll.
ayup, they are very nice when you have a car with an uncalibrated
temperature gauge. Turns out 3/4 scale on a '55 Studebaker converted to
12V with the gauges running off a 6V "Runtz" voltage dropper (probably
not a configuration the factory anticipated <G>) is about 180 degrees -
a little warm for the stock 160 degree thermostat, but not so bad for a
'63 Avanti engine with a factory 170 degree 'stat, actually running a
180 stat because you can't get a 170 anymore.
Had I not had the IR thermometer, I might have ASSumed that I had an
overheating problem when in fact it was a gauge calibration issue.
replace "fly" with "com" to reply.
On Thu, 18 Jan 2007 17:46:27 -0500, "Stormin Mormon"
Does it work for finding cold leaks into the house, or heat leaks out
of the house? I mean, can you point it at the edges of the door or
window or pipe and get a temp reading off of air that is blowing in or
out, or do only solid things radiate IR?
Gases don't radiate, generally, but you might sense lower-temp wood trim.
Or feel around the door with your hands on a cold day, with a large window
exhaust fan running. You can find which rooms have the largest air leaks
and measure airsealing progress with a $70 Kestrel 1000 wind velocity meter
in another partially open window. When you open a door to a leaky room,
the air velocity will decrease. As you airseal, it will increase.
Inexpensive IR thermometers ignore water vapor (so people can use them in
boiler rooms full of steam), so this might also work on a warm summer day.
Don't misunderstand. You're reading the near-absolute-zero temperature of
outer space, through a thin veil of warmer air. The integrated temperature
is still below zero even on a warm night. The clear night sky is a cold
"Ignore water vapor" is fantasy. Blackbody radiation is the same whether
it's a gas, liquid, or solid radiator.
What the radiation thermometer reads, looking at the background of outer
space, overlaid with a transparent but blackbody-radiating layer of
atmosphere. This type of thermometer is performing a digital numerical
integration as part of its analysis of the blackbody spectrum of the
No, your understanding is naive. Ceramics emit radiation like anything
else. Nothing absorbs IR from the darkness of outer space, because there's
no IR to absorb. A room temperature skylight window is emitting IR, not
absorbing it, on a clear night.
Actually, it's doing *both*, isn't it? I think Nick's point was that window
glass isn't nearly as transparent to IR as it is to visible light. Emissions
from an IR source inside the building will be mostly absorbed by the skylight,
instead of passing through, no? Meanwhile, the skylight will radiate IR as
Doug Miller (alphageek at milmac dot com)
I think so, for wavelengths longer than 3 microns.
Sure, but we were talking about sky vs skylights, no? A cheap IR thermometer,
eg Raytek's $99 version, will ignore water vapor absorption and read a lower
sky temp than an expensive one, eg a $1000 Exeltech, which will read a lower
sky temp on a cloudy or humid day.
Yes and no. Yes, it absorbs some incident radiation instead of directly
transmitting it (depending on wavelength). But it re-radiates much of what
it absorbs, which is an indirect transmission.
There is a mythical version of "glass blocks IR" that some people think
makes cars hot on a sunny day. In fact it is the *transmission* of shorter
IR sunlight (many 1000s deg K blackbody) via the glass into the car
interior, where it is absorbed on the interior surfaces, and re-radiated at
longer IR spectra (several 100s deg K blackbody) that is blocked by the
A pane of glass transmits about 90% of the terrestrial solar spectrum
(which has very little power at wavelengths longer than 2.5 microns)
and blocks almost all of the IR spectrum longer than 3 microns. Wien's
displacement law says an 80 F (282K) black body has a spectral peak
at 2897.8/282 = 10 microns... 966K (1279 F) has a 3 micron peak.
Windows transmit a lot more beam sun power than the IR they reradiate,
since houses scatter and absorb incoming sun over a large interior
surface and do not contain IR beam suns of their own.
Glass blocking IR makes cars hot in the sense that without glass, they
would be cooler. Polycarbonate also blocks IR. Polyethylene doesn't.
My sunspace with 256 ft^2 of poly film glazing seldom reaches 100 F
on sunny winter days.
No, like all matter, the atmosphere both emits and absorbs radiation. At
night it emits more than it absorbs (thus cooling itself while keeping us
warm down here, happily), so it is a net emitter, not an absorber. When
you point your Raytek at the clear night sky, you are measuring that
emission. If the atmosphere (net) absorbed IR, the sky would feel
cryogenic like outer space, instead of just somewhat cooler than the
surface, on a warm, clear night.
There is this mythology of the atmosphere (glass, etc.) being nothing but a
sink for radiation. Just enough physics to get it wrong. Typical of
global warming advocates.
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