PSN-L Email List Message

Subject: RE: Microseism filter
From: Bob Hancock Bob.Hancock@............
Date: Thu, 24 Feb 2005 07:24:38 -0700


I purchased a CME 4111 (previously called a CME 2123) Russian MET
seismometer back in the spring of 2002.  The unit had an advertised pass
band of 60 seconds to 50 hz.  I have experienced some problems with the
instrument over the time that I have owned it.  However, these problems have
all been overcome and have not detracted from the overall usefulness of the
instrument, and my pleasure with it.  I particularly like the fact that it
is a plug and play instrument and does not require a mass lock.  The
instrument also required the use of a differential receiver which Larry
Cochrane was kind enough to put together.

 

While checking with other folks, including some professional seismologists,
I found they had reviewed the MET instruments and that there are some
problems in maintaining the accurate calibration required of professional
instruments.  I have had to adjust the advertised sensitivity numbers to
bring the instrument more in line with its current sensitivity.  However for
the overall study of seismic waves on all three channels, and seismology in
general, it's a great instrument, and is virtually maintenance free.

 

Overall, I have been impressed with the instrument.  It is great as it does
not require the periodic leveling adjustments of Lehman type instruments.  I
dug a hole in the front yard, and set a 12 inch square, 2 inch thick cement
block in the ground. I covered the instrument with a plastic bag and covered
that with dirt.   The instrument is currently resting on the cement block
doing its thing.  It is an extremely sensitive instrument and I like it.  I
periodically have compared the wave forms received with nearby professional
instruments and believe the instrument does a good job.

 

Bob Hancock

Tucson, AZ

 

  _____  

From: psn-l-request@.............. [mailto:psn-l-request@............... On
Behalf Of Dave Nelson
Sent: Thursday, February 24, 2005 00:53
To: PSN-L@..............
Subject: Microseism filter

 

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 cutoff.

 

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)
















I purchased a CME 4111 (previously called a CME 2123) Russian MET seismometer back in the spring of 2002.  The unit had an advertised pass band of 60 seconds to 50 hz.  I have experienced some problems with the instrument over the time that I have owned it.  However, these problems have all been overcome and have not detracted from the overall usefulness of the instrument, and my pleasure with it.  I particularly like the fact that it is a plug and play instrument and does not require a mass lock.  The instrument also required the use of a differential receiver which Larry Cochrane was kind enough to put together.

 

While checking with other folks, including some professional seismologists, I found they had reviewed the MET instruments and that there are some problems in maintaining the accurate calibration required of professional instruments.  I have had to adjust the advertised sensitivity numbers to bring the instrument more in line with its current sensitivity.  However for the overall study of seismic waves on all three channels, and seismology in general, it’s a great instrument, and is virtually maintenance free.

 

Overall, I have been impressed with the instrument.  It is great as it does not require the periodic leveling adjustments of Lehman type instruments.  I dug a hole in the front yard, and set a 12 inch square, 2 inch thick cement block in the ground. I covered the instrument with a plastic bag and covered that with dirt.   The instrument is currently resting on the cement block doing its thing.  It is an extremely sensitive instrument and I like it.  I periodically have compared the wave forms received with nearby professional instruments and believe the instrument does a good job.

 

Bob Hancock

Tucson, AZ

 


From: psn-l-request@.............. [mailto:psn-l-request@............... On Behalf Of Dave Nelson
Sent: Thursday, February 24, 2005 00:53
To: PSN-L@..............
Subject: Microseism filter

 

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 cutoff.

 

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)


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