PSN-L Email List Message

Subject: Re: Crossed wire mass pendulum signal extension/s
From: tchannel1@............
Date: Sat, 20 Sep 2008 10:12:20 -0600

Hi Brett,  I did try simple mockups and tested both the "Balance-Like" and 
the "Nearly Balanced".   Found both did work to produce long periods.
I completed the "Nearly Balanced" complete with coil and magnet.   After 
some testing I found it just did not respond to events as the Lehman or 
Vertical.  Can't say it did not respond at all, but it failed for me, so I 
rebuilt the sensor into something else.

Could you explain or give an example of  linear acceleration forces?  A 
Pendulum on a spring, can move up/down, left/right, front/back and twist. 
Let's say the pendulum is restrained, as in this device, so it can not move 
front to back.  Would this device not swing left/right in the same manner as 
a pendulum on a spring,  a clock pendulum?

Thanks, Ted

----- Original Message ----- 
From: "Brett Nordgren" 
Sent: Saturday, September 20, 2008 8:34 AM
Subject: Re: Crossed wire mass pendulum signal extension/s

> Ted,
> One comment on that paper, not related to the design you were discussing: 
> It also describes  the 'Balance-like physical pendulum' and the 
> 'Off-center or Nearly balanced physical pendulum'.  Both these designs can 
> have almost zero restoring force and hence very long periods.  However 
> they also have almost zero sensitivity to linear acceleration forces and 
> are therefore pretty much useless for sensing ground motion.  That 
> limitation wasn't made very clear in the paper.
> Though I guess in that respect they do act a bit like using feedback, in 
> that you trade reduced sensitivity for an extended lower corner frequency. 
> However, they would exhibit none of the response-flattening that you would 
> see when using feedback.
> Regards,
> Brett
> At 08:06 AM 9/20/2008 -0600, you wrote:
>>Hi Folks,  This is one approach I have not tried. 
>>Has anyone built one, as a mock up to see the results?
>>If someone would suggest some dimensions, I would like to try it, to see 
>>how it would work and the period possible.
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