On Wed, 26 May 2004 06:35:16 -0400, "David J Windisch"
wrote:
(How) Is it possible with metrology (that I can afford, much less obtain use
thereof), for me to know without a reasonable doubt what the proportions of
plate-glow due to little-r-sub-little-p and "reflected power from the
mismatch" are?

Are there other sources of plate glow?

Hi David,

Two methods come to mind: Calorimetry and Optical Thermometry.

Both are ancient methods, which means with patience and care you can
achieve very good precision and decent accuracy.

For the Calorimetric approach, simply enclose the tube inside an air
plenum with a good steady stream of air whose temperature is measured
going in, and coming out. To increase efficiency and accuracy, you
would want to build a diffuser into the stream to reduce turbulence (a
4 in diameter honey comb of straws cut 3 or 4 inches long would do
nicely). It would also be nice to draw the air from a relatively
stable temperature source and vent it away (no mixing).

You would then need to research the formulas to convert the heat gain
into watts. I won't go into that at this time.

As for the Optical Pyrometer (the actual term), this consists of a
binocular where one eye looks at the plate surface, and the other eye
is looking at a heated wire. An alternative is a monocular where the
eye looks at both at the same time (more accurate) where the wire
overlays the target image. You adjust the heated wire to luminescence
and when its temperature is equal to the temperature of the target,
the monocular view will offer the wire disappearing! In other words,
you have a bridge circuit and when both heated elements are balanced
the eye registers a null.

You would need a stable source of repeatable current settings so that
you can make differential measurements (the most precision) and
perhaps another target that you can directly measure heat and power
applied (the most accurate). For a wire, go to a junk store and buy
an old toaster. Each element is roughly 50 Ohms (not suitable for
precision RF however). Such a method can with care map temperatures
to within degrees.

I commend your desire to sit down to the bench and sweep away the
cobwebs of musty philosophies traded here.

73's
Richard Clark, KB7QHC