PSN-L Email List Message

Subject: Re: Seismograph noise problem
From: Roger Sparks rsparks@..........
Date: Mon, 11 Feb 2008 06:35:25 -0800

Hi Larry,

The description of your seismometer seems very similar to mine, except
for the mount of the sensor cover.

I drilled three holes in the concrete floor, then put expansion bolts
in.   The result is three 1/4 inch bolts extending about 2 inches above
the rug.

On top of these three bolts I laid a 3/4 inch thick particle board large
enough to support the seismometer cover.  I stepped on the board both to
seat it and to ensure that the supporting bolts were solid.  As I
recall, I re tightened  the bolts after the first  step-on,  and
repeated the procedure.

I took the precaution of supporting the seismometer cover with three
support points, to prevent rocking of the cover.  It sounds like you
accomplished the same thing with flexible/soft cover supports.   My
seismometer goes inside of the cover.

I am very satisfied with the mounting now.  You can see my occasional
postings from Ellensburg, Wash. on the PSN web site.

Good luck,

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> Subject: Re: Seismograph noise problem
> From:    Larry Conklin 
> Date:    Sun, 10 Feb 2008 10:39:43 -0500
> Hi Roger,
> I it very interesting that you have had a similar problem, and I 
> appreciate your suggestions.  I my case, the sensor in in the basement, 
> sitting on a concrete floor.  Several years ago I epoxied three small 
> aluminum plates to the floor for the settling screws to sit on.  My 
> concern at the time was that turning the leveling screw against the 
> concrete was grinding into the floor, leaving concrete dust under the 
> screw.  One of the probable flaws in my construction is that the 
> leveling screw is very small (#4) and more than likely not really firm 
> enough.  But, when I'm not being "haunted" the thing performs pretty 
> well.  Seems like problems stemming from the mechanical design shouldn't 
> be episodic the way I have having them.  I am using a 3 point mount, and 
> the other two feet (base of the triangle) are sturdier.
> One thing that your comments encourage me to revisit is the way the 
> cover over the sensor is made.  It is made of 1/4/inch particle board 
> and a little heavy on the heavy side.  I is just sitting on the base 
> frame of the sensor, held down by it's own weight.  There are soft 
> plastic feet attached where the contact is made to the frame.   I don't 
> normally make a point of pressing everything down to reseat things after 
> i adjust it.  Never occurred to me to do that.  One thing I did try 
> since this last episode started was to put a little piece of tape under 
> each foot, to introduce a little "sqisshyness" to prevent the kind of 
> "micro-rocking" that you apparently had.  I didn't see any obvious 
> difference.
> Guess I'm going to have to embark on a real science project.
> Larry


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