PSN-L Email List Message
Subject: Re: Microseism filter
From: "David H. Youden" dyouden@.............
Date: Thu, 24 Feb 2005 07:07:13 -0500
Tell me more about your filter. I live on the East coast, and am
troubled by the level of microseisms. I have messed a bit with switched
capacitor circuits in the past, but for different purposes. Could you
send a circuit diagram directly to me? Or point me to the chip you used
so I can puzzle out my own filter.
Dave Nelson wrote:
> I have recently added a Russian ASMET -1V MET broadband seismometer to
> my setup. As I live near the coast the microseism level was dominating
> the noise backgrond to the extent that earthquakes of interest were
> being lost in the " noise". The microseism spectrum is very distinct
> and I felt its elimination would not seriously effect the earthquake
> detection capability .
> I have developed a simple filter based on switched capacitor
> technology that virtualy eliminates the microseism background. The
> filter has no critical componants or capacitors and is tuned by a
> clock frequency. The Q is 0.5 which gives roughly an octave bandwidth
> centered at 0.015 hz or 6.6 seconds . Since the center frequncy is
> clock dependant it can be shifted arbitarily but 6.6 seconds seems to
> work very well. The filter is placed directly ahead of the A/D at the
> highest voltage swing level in the system to avoid adding noise.
> Just two wires -- in and out (plus power of course).
> The results are very good, the harmonic like signal from microseism is
> gone and the effective signal to noise ratio of eathquakes is
> significantly better. The spectrum has a deep null at 6.6 seconds
> instead of a dominant peak .
> I know this kind of spectrum shaping can be easily done in software
> but that is usually beyond the scope of an amateur or computer dum-
> dum like me. The whole thing is two IC's and a 15 hz clock generator.
> ( 100 times the center frequency)
> The Russian seismometer is truely amazing. Virtually plug and play --
> four wires ,no adjustments or critical setup. The respose is
> advertised to 20 seconds but seems to respond well to over 100 seconds
> on the low end and too well to be useful ,given the urban background
> noise ,at the high frequency end. I have another swiched capacitor low
> pass filter switchable to 5, 2.5 and 1.25 hz. to control the high end
> My setup also includes 3 axes of short period based on HS-10-1 1 hz
> seismometers that I found in a surplus store. I am using Amaseis and
> experimenting with Seismowin for analysis and display.
> I am a retired aerospace engineer who spent too much of my career in
> management and I am having a ball doing the seismology thing.Good to
> be back doing some development and putting the old brain to work. I
> intend to do some seismometer development as my next project -- I have
> some ideas for some different ,but not outrageous, concepts which
> may ( or may not ) work.
> I would be glad to correspond with anyone interested in or commenting
> on what I am doing.
> Dave Nelson ( California not New Zealand)
Public Seismic Network Mailing List (PSN-L)
[ Top ]
[ Back ]
[ Home Page ]