PSN-L Email List Message

Subject: Re: Incresing the period of a lehmans seismomter ?
From: Mark Robinson mark.robinson@...............
Date: Sun, 10 May 2009 11:59:06 +1200

Jón Frímann wrote:
> Hi all
> Thanks for the help of the weeks. I could not have fixed the issues with
> out you all.
> I am still having minor issues adjusting the period of my lehman sensor.
> I am not sure if I have to move the boom up or down to increase the
> period of my sensor.
> Regards.
> Jón Frímann.

Hi Jón,

It's not a matter of moving the boom up or down but of moving the axis closer 
to vertical. The axis being the line through the two bearing points.

You are faced with the tradeoff of period versus stability

Looking at the pictures of your seismograph I see a few things I'd work on.

I'd like to see some triangulation between the vertical and horizontal parts of 
the frame. Rigidity of the frame is critical for stability.

The turnbuckle looks a bit rough. Some dabs of weld on the hooked joins should 
improve stability. I'd probably replace the whole arrangement with a single 
piece of (at least partially threaded) rod.

All the best

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