Owen Duffy wrote:
On 4 Dec 2006 06:07:44 -0800, "Denny" wrote:

...
So I purchased an Infrared measurement gun...

fascinating little instrument - did you know that on a clear day with
the air temperature +12.1 F and zero wind, that a 5 foot diameter
black rubber tractor tire facing the clear sky to the North can have a
surface temp of -2.6 to -3.0 F? I didn't but that is what I found...
OK, I digress again

It is not such a digression.

You should do make measurements of the temperature of different
materials that you know are at the same temperature, and see what
results you get from your non-contact thermometer.

The emissivity of the surface is an important factor that limits the
absolute accuracy of these things.

It is an interesting experiment that you have described, though I am
not sure that surface temperature (if it is accurate) alone is a good
indicator of the power flow to the air. For example, would you expect
that the temperatures of natural coloured and black aluminium heatsink
to be the same if dissipating the same (non zero) power in the same
environment? Extending that to your experiment, is dark enamelled
copper wire (as may be used in a coil) a better black body radiator
than bright aluminium (as may be used in a capacitor).

Owen
--

Actually, unless the heat sink gets pretty hot relative to its
surroundings, a large percentage of the heat loss is convective, not
radiative, assuming we're operating in air at normal atmospheric
pressures. It all gets much more interesting in a good vacuum.

If I got the numbers right, for example, blackbody radiation at 280K is
about 35 milliwatts/cm^2, and at 300K it's about 46 milliwatts/cm^2.
So 20C above roughly room temperature ambient gets you a whopping net
11 milliwatts/cm^2 to radiation. (Fins facing each other don't help
radiation, but do help convection.)

Cheers,
Tom

Owen Duffy wrote:
On 4 Dec 2006 06:07:44 -0800, "Denny" wrote:

...
So I purchased an Infrared measurement gun...

fascinating little instrument - did you know that on a clear day with
the air temperature +12.1 F and zero wind, that a 5 foot diameter
black rubber tractor tire facing the clear sky to the North can have a
surface temp of -2.6 to -3.0 F? I didn't but that is what I found...
OK, I digress again

It is not such a digression.

You should do make measurements of the temperature of different
materials that you know are at the same temperature, and see what
results you get from your non-contact thermometer.

The emissivity of the surface is an important factor that limits the
absolute accuracy of these things.

It is an interesting experiment that you have described, though I am
not sure that surface temperature (if it is accurate) alone is a good
indicator of the power flow to the air. For example, would you expect
that the temperatures of natural coloured and black aluminium heatsink
to be the same if dissipating the same (non zero) power in the same
environment? Extending that to your experiment, is dark enamelled
copper wire (as may be used in a coil) a better black body radiator
than bright aluminium (as may be used in a capacitor).

Owen
--
(I apologize for not thinking of this in time to include it in my
previous posting...)

Remember, too, that what looks "black" to us in the visible spectrum
may be quite different over the spectrum including most of the
radiation, especially when the object is only about 250K to 350K. At
300K, the peak of black body radiation occurs at about 10 microns, less
than 1/10000th the frequency of visible light. I suppose heat sinks
are dyed black more because we think they should look black than
because it does any good thermally. And avoid buying heat sinks that
are PAINTED black; the paint just adds to the thermal resistance.

Cheers,
Tom

K7ITM wrote:
Owen Duffy wrote:
On 4 Dec 2006 06:07:44 -0800, "Denny" wrote:

...
So I purchased an Infrared measurement gun...

fascinating little instrument - did you know that on a clear day with
the air temperature +12.1 F and zero wind, that a 5 foot diameter
black rubber tractor tire facing the clear sky to the North can have a
surface temp of -2.6 to -3.0 F? I didn't but that is what I found...
OK, I digress again

It is not such a digression.

You should do make measurements of the temperature of different
materials that you know are at the same temperature, and see what
results you get from your non-contact thermometer.

The emissivity of the surface is an important factor that limits the
absolute accuracy of these things.

It is an interesting experiment that you have described, though I am
not sure that surface temperature (if it is accurate) alone is a good
indicator of the power flow to the air. For example, would you expect
that the temperatures of natural coloured and black aluminium heatsink
to be the same if dissipating the same (non zero) power in the same
environment? Extending that to your experiment, is dark enamelled
copper wire (as may be used in a coil) a better black body radiator
than bright aluminium (as may be used in a capacitor).

Owen
--
(I apologize for not thinking of this in time to include it in my
previous posting...)

Remember, too, that what looks "black" to us in the visible spectrum
may be quite different over the spectrum including most of the
radiation, especially when the object is only about 250K to 350K. At
300K, the peak of black body radiation occurs at about 10 microns, less
than 1/10000th the frequency of visible light. I suppose heat sinks
are dyed black more because we think they should look black than
because it does any good thermally. And avoid buying heat sinks that
are PAINTED black; the paint just adds to the thermal resistance.

Cheers,
Tom

Shoot, make that "less than 1/10th the frequency of visible light," but
still darned little radiated in the visible region.

There's cool 'speriment using a spherical flask of visibly opaque
liquid to focus IR radiation to a point where you can feel it very
easily. What you see in the visible spectrum isn't what IR "sees."

Cheers,
Tom

K8DO writted: :-)

So I purchased an Infrared measurement gun...

So what kind and price?

73 Yuri

On 4 Dec 2006 06:07:44 -0800, "Denny" wrote:

fascinating little instrument - did you know that on a clear day with
the air temperature +12.1 F and zero wind, that a 5 foot diameter
black rubber tractor tire facing the clear sky to the North can have a
surface temp of -2.6 to -3.0 F? I didn't but that is what I found...
OK, I digress again

Hi Denny,

More fascinating was that everyone missed the significance of the
reported temperature.

The coil was found to be +12.9 to +13.1 F and the condenser plates were
+31.5 to +32.3 F... A result which sent me away mumbling to myself...
Not what I expected...

OK, another surprise.

we all know that condensers are 100%
efficient and coils are lossy - right?...

Of course, and then the conversation went towards power factors and
such. Didn't Georg Simon Ohm die for all your sins, folks?

You need another specialized piece of test gear - in tribute to our
departed Reggie's folk-hero: a Kelvin Bridge Ohm Meter. Don't ask for
one at Radio Shack. When (and if) you get one, try measuring the
resistance of your home made cap (and I don't mean lead-to-lead, but
lead-to-plate, and for each plate, and for each lead connection).

For those who would press a Radio Shack Ohm Meter into this service, a
gratuitous -Chuckle-

73's
Richard Clark, KB7QHC

Richard, I doubt many of us have to go buy a Kelvin Bridge Ohmmeter
from eBay to get what you're after.

I've got a Radio Shack meter with a 300mV scale; I've got a hefty power
supply with current limit, and I've got a 55 watt, 12V fog lamp. I'll
admit, I had to think pretty hard to figure out where I had a load
resistor to keep my power supply from going into overcurrent shutdown,
but it's on the premises, so it counts ;-)

I think I can do milliohm measurements of no more dubious accuracy than
the voltage and current accuracy of my Radio Shack meter in the
vicinity of 4.5A and 4.5mV

Long live four wire resistance measurements! Denny, I'd be interested
in whether or not lead resistance was a major loss component if you
want run a few amps DC through your cap lead / plate connection and
measure the voltage drop.

73,
Dan

On 4 Dec 2006 22:20:34 -0800, "
wrote:

Long live four wire resistance measurements!

Hi Dan,

A Cigar to the man who knows how to parlay Radio Shack into a winner!

73's
Richard Clark, KB7QHC

In my usual habit I'll reply off the bottom of the que... Lots of good
comments and suggestions...
In no particular order:
I suspect the surface of the black tire had cooled below ambient by
convective radiation... Happens to my windshield on mornings above
freezing ambient whilst the windshield will be a skim of ice...
Though the thought of what the tire might read under non-convective
conditions occurred and was duly filed away in that great container in
my head for further inspection... Actually I use the Rubble Method for
filing information.. That is everything in my head is tossed on a
great heap of rubble, and as I stir through the pile looking for one
item, interesting bits of flotsam and jetsam flow back to the top of
the heap for inspection, "oooh ya, I remember that!"

Yes, the thought that there might be unwanted resistance in the
connections to the condenser plates occurred and remains to be
investigated... The connecting wire is the #10 magnet wire forming the
coil and is firmly bolted with #8 brass hardware and flat washers to a
1"x1" tab formed on the edge of the plate when I cut the plates from a
sheet...

For Yuri, congratulations on the CQ160 win(s), nice job my friend...
Drop me a description of his antenna setup... Wanna be's like me are
always looking for an edge...
On the IR gun, it was in the ~$65 range on sale, as their economy
model, I don't remember who the internet vendor is, I can get you the
make and model if you need it... But just do a search, lots of sources
and prices... The little bit I have used it I have been satisfied with
the readings - nothing rings my 'no-way, Jose!' meter, so far... The
35' long radiant tube heater in my shop shows ~375-385 F at the mid
point from 8 feet away, which is about right as it will not ignite
paper on contact I tried though it makes it brown - paper has an
ignition temp of ~454 F per Ray Bradbury at least... The gun has a
laser spot so you can see where the detector is aimed and the size of
the spot is proportional to the area being measured at that distance...

I suspect that dielectric loss in the soda glass is the prime
contributor to the temperature rise on the plates... There is a
significant amount of joules passing through the glass as strain in the
dielectric..

Oh yeah, the question on the type of glass... Bad habits as an old lab
rat surfaced when I wrote that... Common window glass is float formed
on molten tin, and that is what my old chemical stained brain popped
out as 'stannous'...

On differential IR readings from the surface of various materials -
well I can't say for sure as my credentials in thermodynamics are shaky
at best (picture me shuddering in pain at the memories of Schrodinger
equations and those IBM punch cards we used to program the computer in
the physics lab 40 years ago - 'the horror, the horror'..... But, all
the materials in the tuner were within a few tenths when at ambient, so
I have no reason to suspect a gotcha when midly warmed...

denny / k8do - often confused but never in doubt...

Brain fart - substitute "radiation cooling" for 'convective cooling' in
my last post..
The thought struck me as I was wandering down the hallway that I had a
senior moment when I used the term convective for cooling to the sky by
radiation, duh...

denny - hey, even Einstein had his moments see Cosmological Constant

K8DO wrote:

For Yuri, congratulations on the CQ160 win(s), nice job my friend...
Drop me a description of his antenna setup... Wanna be's like me are
always looking for an edge...
On the IR gun, it was in the ~$65 range on sale, as their economy
model, I don't remember who the internet vendor is, I can get you the
make and model if you need it... But just do a search, lots of sources
and prices... The little bit I have used it I have been satisfied with
the readings - nothing rings my 'no-way, Jose!' meter, so far...

Any info on the IR gun would be appreciated, sounds, like right one for what
I want to use it (check the loading coils etc.)

Thanks! Wal's station rocks, even with this rusty OF. I put some pictures on
our Tesla web site www.TeslaRadio.org, click on PHOTOS and W8LRL. It will be
our goal to beat it from N2EE. We just came back from some slave labor of
love, clearing more brush in freezing windy WX, leveling the field for RF
:-) Waitng for the swamp to freeze so we can walk around and fix the
antennas.

73 Yuri, K3BU