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

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.

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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