On Fri, 07 Apr 2006 23:59:55 -0400, Jeff Wisnia
wrote:

Jeff Wisnia wrote:

Martin H. Eastburn wrote:

The one we had at home as a kid had a glass hub.

If you have a metal one - did the needle eat it up and finally cut it ?
Have you turned it upside down and such ?


The "hub" looks like an inverted subminiature glass test tube about 5/8"
long and 1/8" ID. A little stamped metal X shaped piece with an extruded
center hole is either press fitted or adhesively attached to its open
end. The paddles are attached to the legs of the X.

My radiometer only has two paddles which are attached to opposite legs
of the X. The other two legs are bare, maybe the manufacturer uses them
when they make four paddle models.

What I prolly should have done before I started this thread was to
slowly move a strong magnet towards the radiometer while it was stopped
to see if it caused any movement or tilting of the vane assembly. That
prolly would have told me whether my assumption that magnetization is
making the metal hub "stick" to the needle has any legs to it.

Dumb of me not to think of that, as right in the next room there's a
pretty strong suspension magnet on the little diamagnetic demo I built a
few years ago.

If you've never played with diamagnetics, it's free floating objects
right before your eyes, sort of counterintuitive to what we usually
think about magnets and/or gravity:

http://home.comcast.net/~jwisnia18/jeff/diamag.html

I'll run a magnet test first before I try demagnetizing with my 250 watt
Weller as suggested.

Report later.....

Thanks guys,

Jeff


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

Ah ****ing ha as we academophobes say now and then.

Static attraction can be a problem. My first job was working with
electrostatically suspended gyroscopes.

Try bombarding your radiometer with UV that might ionize the sparse
gas within enough to dissipate static charge.