Re: [ATM] Temperature sensing and adaptive optics=mirror control

[Ric Rokosz <radicell2@yahoo.com>]

--- Dominic-Luc Webb <dlwebb@canit.se> wrote:

> 
> 
> > control it, not sure if I would use a AC
> diac/triac type design or just
> > batteries and trim pot and/or frequency modulation
>  from 555 or some such.
> > I would need some advice here.

The articles you need are in the SPIE series Vol 4003
Munich 2000 pp406 -416 that details the work done on
the KPNO 4 meter,and pp426 to 435 that details the
work done in France by Lardiere,Arnold and Dejonghe on
a 1.5 meter f/1.7 25mm thick plate glass menicus
mirror,back in 1999.The Arnold article goes into
details of the heating hardware.They used 42
electrodes of different voltages around the edge.

They also mention the work done on the 8 meter Gemini
scope. B.Perona,et al.: SPIE v. 3352 pp868-878 1998).

You can get these articles from the SPIE.org site.Not
cheap.

You might like to check out the software at :
  http://www.fieldp.com
which is finite element software for electromagnetics.

An interesting statement in the Arnold article states
that they found the optical surface of the
mirror(plate glass) is always up to 1 deg C colder
than the rear.Under such a thermal load,plate glass
presents a large amount of defocus and spherical
aberration."Defous can be corrected by a
focuser(manual or automatic) while the s.a.can be
corrected by a surface heating system using common and
simple components>" end of quote.

The most interesting portion of the Arnold article
(for the atm)  is the detail of the edge clip that
transfers the current to the face of the coated
mirror.
They used an elastic metal srtip in a shallow " ]"
shape that has inside it a piece of foam.On top of the
elastic strip they have a piece of conductive copper
adhesive tape.The current wire is attached to the
elastic metal strip.They then use  what seems to be a
sprung type clip that goes over the top of the copper
tape and then under the 25mm piece of glass.

Of course the whole thing is controlled by computer to
regulate the voltage vs the need for correction given
the ambient air temp. 

Ric


		
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