PSN-L Email List Message

Subject: Re: Strong motion sensor design
From: Arie Verveer ajbv@............
Date: Mon, 18 Oct 1999 14:31:36 +0800


Hi, How about this for an idea. We substitute "Salt Water" or a similar conductive
viscous  liquid in a "Mercury tilt meter".

I did a little math's and came out with this startling result. If  we had two containers
3 inches in diameter placed 2 foot apart that is connected with a 1/8 inch diameter
tube and then,  use "salt water" as a conducting fluid.  The  tilt meter would have
a natural frequency of 26 seconds with a dampening factor of 0.89.

Cup's  3 inches       separation 2 foot     period -> 26sec  dampening 0.89
           2  "                              3  "
22sec                   0.73

As regards the electronics, Larry's  "Shackleford-Gundersen" electronics board
is basically all you need.

One thing that should be taken into account, as the water temperature
changes the dampening factor changes. The devices period stays nearly
the same. We may need to substitute the water or add anti freeze in some
cold climates. My seismometer froze !!  Or boiled away !!

I'm sure there is a few problems that have been missed.

Just an Idea.

Arie


>
> Only covering the strong motion range say +/- 2 g it is not hard to come up with a
> lot of different ideas for sensor. The real challenge as I see it is in the
> details of the design. That is picking a design that is easy to manufacture the
> parts or using a design that can be build from common parts such as the STM-8.
>
> The very first sensor I built consisted of a small weight glued to the cones of
> two speakers. It easily detected footsteps across the basement on a concrete
> floor.
>
> We should try and nail down a few specifications so that the discussion don't get
> too far out in left field. How about +/- 2 g max acceleration with 16 bits of
> dynamic range. (How does this match the low end of a geophone sensitivity?) What
> about frequency response? ( 0.01 to 10.0 Hz).
>


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Larry Cochrane <cochrane@..............>