PSN-L Email List Message
Subject: Re: Crossed wire mass pendulum signal extension/s
From: Charles Patton charles.r.patton@........
Date: Fri, 19 Sep 2008 11:43:44 -0700
Meredith,
We're (Brett, Chris and I) putting the finishing touches on a white
paper on pivots with spreadsheet calculations of actual locus points,
errors, etc. that shortly I'll put up on a web site. It includes your
pivot that I'm calling the X-roll. It's problem is that it doesn't have
an easy way of obtaining long periods except the use of force feedback
at which point I would argue that the lever arm extension probably
doesn't add much. I toss out an alternate idea. The paper will include
the equations for something I'm calling the X-suspension that comes from
work on LIGO. It's essentially two flat plates suspended with crossed
wires and a mass attached to the lower plate and adjusted in height
between the the plates. This can be set for any period. It would have
the property you mention, so a lever arm attached to the bottom plate
and extended away from the bottom would magnify the movement. I haven't
done it yet, but it seems to me that although for the LIGO work they
used flat flexures with traditional clamps, the scheme is very amenable
to use of rolls and wire or bands for very low friction. I think it
could be accomplished with 3 bands minimum, but 4 equal width bands
would make construction easier and very high Q.
Regards,
Charles Patton
meredith lamb wrote:
>
> Hi all,
>
> If one considers that a suspended gravity centered and reasonably
> balanced mass on a pair of
> crossed wire pivots, actually slightly enertia rolls in horizontal
> response to a seismic signal;
> would it be enticing to attach to the mass, a light weight mechanical
> arm/flag to amplify
> such rolling offset signals? The natural period will of course be
> short, but displacement sensors
> can elongate the periods recorded.
>
> I would think the flag/arm extension could best be put/directed
> vertically up from the mass to
> limit the physical seismometer horizontal size; and it could literally
> be of any reasonable length
> that hopefully doesn't upset the mass balance position.
>
> Of course; a light signal mirror on the mass could do the same thing
> with ~ effort, and not
> influence the balance position.
>
> One could entertain a variety of mass attached velocity or displacement
> sensors or feedback
> from such.
>
> Has anyone tried a resemblance of this? Results? Problem/s? Missed
> points?
>
> Take care, Meredith
>
>
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