PSN-L Email List Message

Subject: Re: Another horizontal boom/mast pivot to consider
From: Bobhelenmcclure@.......
Date: Thu, 28 Nov 2002 23:01:58 EST


Hi Charles and Chris,

  If you want to float your horizontal seismometer in Silly Putty or 
whatever, you must have flotation stability.  If you have a 20 second period, 
the effective length of the pendulum is 100 meters.  You have to assume the 
mass of the pendulum is 100 meters above the deck, so far as tipping moment 
in the sensing direction is concerned, and design your "barge" to be stable 
with such a top-heavy load.  This is another reason to use a lightweight 
pendulum.  The "barge" is going to have to be very long in the sensing 
direction otherwise.  It is still worth considering for those who suffer from 
instability from the ground or pier, but you might need to consult a naval 
architect.

  My idea is to mount the sensor on the pivot end of a gimbal-supported 
hanging pendulum, and have the bob end sitting in viscous liquid, but then 
the pier would have to be hollow, like maybe an unused chimney.

Regards,

Bob McClure
Hi Charles and Chris,

  If you want to float your horizontal seismometer in Silly Putty or whatever, you must have flotation stability.  If you have a 20 second period, the effective length of the pendulum is 100 meters.  You have to assume the mass of the pendulum is 100 meters above the deck, so far as tipping moment in the sensing direction is concerned, and design your "barge" to be stable with such a top-heavy load.  This is another reason to use a lightweight pendulum.  The "barge" is going to have to be very long in the sensing direction otherwise.  It is still worth considering for those who suffer from instability from the ground or pier, but you might need to consult a naval architect.

  My idea is to mount the sensor on the pivot end of a gimbal-supported hanging pendulum, and have the bob end sitting in viscous liquid, but then the pier would have to be hollow, like maybe an unused chimney.

Regards,

Bob McClure

[ Top ] [ Back ] [ Home Page ]