PSN-L Email List Message

Subject: Re: Spring Damping.
From: Mark Robinson mark.robinson@...............
Date: Wed, 25 Jul 2007 15:24:50 +1200

Geoffrey wrote:
> I understand that no matter what the setup
> you want the whatever to achive a damping
> where after relese the object attains an
> amplitude on the backswing of about 0.1
> of the relese height.
> It would be nice to understand how this
> translates to Q which is simply the inverse of damping.
> I have found it best to use as little damping as possible
> with a geophone that already has internal damping
> related to construction. especially if you are
> looking below the F0 point.
> If you are only looking for first time of arrival you want
> the greatest sensitivity possible.
> I get the best pictures when my geophone is damped
> the least so i do not understand why everyone
> wants so much damping. But I was told by Mr.Willis Jacobs
> of the USGS that they wanted a 10:1 damping ratio.
> Release at 10 and on each half cycle it will be
> only 10% the previous amplitude.
> Does anyone know the proper formula to
> translate swing amplitude to Q or its inverse
> called damping ?
> 10:1 = _____Q ????

Hi Geoffrey,

A tuned radio frequency circuit and a seismometer have opposite goals, 
especially if you are interested in the spectrum of the signal per your 
discussion of FFT techniques.

In order for the FFT to have any meaning you need a dataset produced by a 
broadband sensor with as near as possible a flat frequency response. This is 
what you get with a critically damped system and is precisely not what you get 
with a high Q tuned system.

I am unfamiliar with WinXP, but on Win98 getting a full screen MS-DOS type 
window by holding down Alt and pressing Enter while in an MS-DOS command prompt 
window seems to dispose of much of the Windows overhead.

I assume that QuickBasic is a compiled Basic and not an interpreted one. A 
compiled language usually runs at least ten times faster than an interpreted one.
Mark Robinson
24 Jul 1952 Democrats choose Adali Stevenson and Alabama Senator John Sparkman
             to run for the White House.
24 Jul 1982 Anna Pacquin, actress, born.

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