PSN-L Email List Message
Subject: Re: nonlinearities
From: Brett Nordgren brett3nt@.............
Date: Sat, 13 Aug 2011 18:38:41 -0400
Dave,
I took some data from one occasion when you had baked a spring
showing the noise before and after.
See: http://bnordgren.org/seismo/YumaBefore%26After.pdf
Brett
At 06:12 PM 8/13/2011, you wrote:
>All,
>
>The simple fact remains -- Feedback seismometers are the world
>standard. No other technology can come anywhere near their
>performance and operational flexibility.
>
>Their noise levels and bandwidth of the typical off the shelf
>instrument from several sources are such that the only area where
>significant improvement is desired relates to extremely long period
>performance for the study of whole earth modes at 1000 seconds and longer.
>
> Most of the development activity is related to making smaller and
> less expensive instruments and greater flexibility in
> installation. One significant exception is Metrozet where a new
> instrument to replace the STS-1 is under development.
>
>Non feedback instruments are a relic of the past or short period
>geophone or geophone-like instruments which have their niche in
>local event monitoring and the amateur community.
>
> The optical open loop instrument is unlikely to have any success
> (in my opinion) simply because it will never be stable. When I
> fist read the paper I concluded the project had no chance of
> becoming an operational instrument but it was an interesting a
> academic exercise. Others with the best credentials in the business
> have shared that sentiment.
>
>Regarding creep effects -- When a spring is first installed in an
>instrument there will be "pops" related to what is probably
>dislocation effects in the spring material . Their frequency will
>gradually reduce in time. The solution is too bake the assembly,
>with the spring at its operational stress, at ~ 160 C for several
>hours. This will essentially eliminate the effect.
>
>After the bake the spring can be removed and reinstalled as long as
>the stress is applied in the same direction upon
>reinstallation. The springs in my instruments are typically at a
>stress of 150,000 to 190,000 psi with a yield strength of ~300,000
>psi. (17-7 stainless treated to CH900 condition )
>
>
>Dave Nelson
>Rolling Hills Estates , California
>
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