Lew Hartswick wrote:
Jeff Wisnia wrote:


Well, when I got home tonight the first thing I did was take a high
energy magnet and move it toward the radiometer, which was in dim
light and not turning.

The magnet had no effect on the vane assembly, it didn't tilt, wiggle
or twitch even when the magnet was right against the glass bulb.

So much for my thinking it was magnetism causing the metal X piece of
the hub to stick to the needle.

Looking at the hub assembly under magnification, the metal X piece
looks like it's likely made of aluminum.

But, the "sticking" effect was still there, With the rotor well
centered on the needle, if I tilt the bulb slightly so the hole in the
metal X piece stars moving off center with respect to the needle it
soon reaches a point where the rotor will suddenly "jump" the rest of
the way so the hole in the X piece hits the needle with an audible
click and sticks there even when I return the unit to an upright
position. I have to jiggle it until the rotor ends up centered asgain.

I'm thinking now it's probably an electrostatic effect, but I don't
know what may have happened to make it to start happening now. I'm
pretty sure It didn't do that a dozen or so years ago when it was new.

I tried wiping the outside of the bulb with some antistatic fluid we
use on the glass of our photocopier, but that didn't help.

I guess nothing lasts forever.....

Jeff


Hey! Has anyone suggested that it may be a result of "deforming" the
tip of the needle or the bearing that rests on it???? Some sort of a
"ring" worn in the bearing or some "unspecified" deformation of the
needle.
Some more examination please.
...lew...

Doubt it lew, read on....

First, after I posted last night I tried a three turn coil of #12 wire
in my 250 watt Weller gun carefully moved over the bulb while it was on
and removed several feet away before I released the gun's trigger. It
did squat about removing the "sticking" effect.

So, the radiometer and I went to sleep for the night and when we woke up
early this morning we were BOTH back to normal. It was overcast outside
at dawn and there wasn't enough sunlight coming in through the window to
move the radiometer.

But, to my angst and amazement it no longer displayed that "sticking"
effect. I could slowly tilt it to from side to side and the rotor stayed
horizontal until the needle reached the limits of the hole in the X
shaped metal piece. No sudden "jumping" effect anymore.

Poiting a flashlight at it made it start turning.

I'm now strongly leaning toward it being an electrostatic effect and the
charge(s) must have leaked off in the dark overnight.

Maybe there's a photoelectric effect from the coatings on the vanes
which makes the rotor assembly charge up after light hits them for a
while. The "light" sides of the vanes look like they're covered with a
light yellow paint and the "dark" sides look like they're matte black paint.

'Tis interesting to say the least. I've posted to sci.physics to see if
the effect my radiometer displayed is perhaps known and understood by
some of the cognicenti there. Thus far all I've received on that
newsgroup are a couple of useless remarks made by people who sound like
their entire alimentary tracts have somehow become reversed.

Jeff
--
Jeffry Wisnia

(W1BSV + Brass Rat '57 EE)

"Truth exists; only falsehood has to be invented."