PSN-L Email List Message

Subject: Re: Equipment: SG vs. Lehman...Hybrid
From: "Travis Farmer" travis5765@...........
Date: Fri, 25 May 2001 21:19:30 -0400

But doesn't a CCD have pixels?
i would think this would create kind of a stepping data output.
Though i have never actualy seen a CCD array so i may be compleatly wrong.
By chance have you got a schematic i can study?


>Hi Chris,
>You are almost there-forget the photocells and use a CCD
>linear array
>and a laser beam reflected off the vertical pendulum. The
>CCD array
>gives you a clean, robust output that is a direct analog of
>of the seismic mass. Hence it is not frequency-response
>limited. It is
>truly an absolute position sensor, rather than the classic
>sensor with all its' attendant problems. I am cobbling up a
>using the guts from an old HP Laser-Jet printer.  Another
>method is to monitor the relected laser beam with a simple
>interferometer and count the resulting fringe patterns. This
>is done in the
>USGS gravity observatory instrument here in Boulder. Now you
>measure displacements down to to wavelength of whatever
>color of
>light your laser is!!
>Best wishes-
>Dave Latsch
>ChrisAtUpw@....... wrote:
> > In a message dated 25/05/01, travis5765@...........
> > writes:
> >
> >
> >> Although I have not tried it, it seems like it should
> >> work. You would have
> >> to make sure NO excess light fell onto the sensors
> >> though.
> >> By the way, I missed the page in scanning that told that
> >> the output needs
> >> only minimal amplification though it varies with the
> >> rated output of the
> >> solar panels and the consistency of the light output.
> >> My idea for a modification would be to use a laser
> >> pointer as a light
> >> source. make sure to have a well regulated power supply
> >> for it.
> >
> >       The larger area silicon photocells as opposed to
> > 'solar cells' tend to
> > be better matched as to sensitivity, change with
> > temperature and reverse
> > leakage. Solid state Lasers are very noisy indeed. LED's
> > are also noisy and
> > their output is quite temperature dependant. A tungsten
> > bulb driven from a
> > voltage stabilised source at about 3/4 it's rated voltage
> > will give good
> > performance. You also benefit from the Infra Red
> > sensitivity of the Si cell.
> > You can get good performance by butting two cells end to
> > end and using a slit
> > which exposes about half each cell.
> >
> >       Regards,
> >
> >       Chris Chapman

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Larry Cochrane <cochrane@..............>