Myself, being new to the hobby, I would like more information about this 
"Volksmeter" devise described in this letter.  Where may I find more, photos 
and etc.

Regards,
Jerry

  ----- Original Message ----- 
  From: Larry Cochrane
  To: psn-l@..............
  Sent: Wednesday, December 06, 2006 3:50 AM
  Subject: Simple pendulum response


  Hi Everyone,

  Dr. Randall Peters asked me to forward the following message to the list.

  Regards,
  Larry Cochrane
  Redwood City, PSN

  I've been following with interest the discussions concerning instrument
  characteristics.  Now that my schedule is easing somewhat, I felt that I 
should get
  involved.  Should it happen that any of you respond to these comments and 
don't hear
  back from me for a while, it's because I will be away for about a week to 
the Amer.
  Geophys. Union Fall Conference in San Francisco (starting 11 Dec.). There 
I will give
  a 15 minute oral presentation titled "State of the art Digital 
Seismograph" .  The
  abstract is posted at
  http://www.agu.org/cgi-bin/sessions5?meeting=fm06&part=S14B&maxhits=400

  The instrument which will be described (and also demonstrated at one of 
the booths)
  uses a "simple" compound pendulum with a natural frequency of 0.92 Hz.  It 
employs my
  fully differential capacitive detector as a displacement sensor (array 
form), with
  electronics based in Analog Devices' new award winning capacitance to 
digital
  converter integrated circuit (AD7745).  Kudo's to our own Larry Cochrane 
as the
  brains behind all of (i) the electronics hardware necessary to do the I2C 
logic
  operations required of the chip, and (ii) the software operating system in 
the form
  of WinSDR and WinQuake.

       For those of you who have been monitoring Larry's instruments at
  http://seismicnet.com/quakes/images
    you may have noticed two real-time helicord records generated by the
  single-pendulum instrument (N-S orientation) that he placed online.  The
  raw-data-train is lctst.gif, which has been high-pass filtered (corner 
frequency of
  10 mHz) before display.  The unfiltered waveform is available via download 
upon
  request from Larry.  This lctst is best suited to the real-time display of
  earthquakes local to the Redwood City, CA site.

        For registering teleseismic earthquakes real-time, Larry has also 
provided
  lctst1.gif, which is the numerical integration of lctst after first doing 
a high-pass
  filter.  This operation on the VolksMeter's output provides a display 
similar to what
  is provided by 'bandwidth extension' using electronic means in other 
instruments such
  as geophones.

         I was pleased to see John Lahr provide links on his webpage 
describing (i)
  transfer function differences between velocity and position sensing, and 
(ii)
  discussion of the zero-length spring that was invented by physicist Lucien 
LaCoste in
  the early part of last century.

        There are some things that need seriously to be clarified concerning 
theory of
  seismometers, since there is so much confusion; not only among amateur 
seismologists,
  but also even many professional geoscientists.  Ultimately, the ONLY 
source of
  seismograph excitation (no matter the instrument design) is ENERGY. 
Additionally,
  the ONLY thing that delivers energy to the seismometer is Earth's 
ACCELERATION at the
  site of the instrument.  This is true not only for the instrument's 
response to
  earthquake waves whose periods are shorter than about 300 s, but also for 
earth 'hum'
  in which the instrument responds mainly to tilt, when the periods are 
greater than
  about 300 to 1000 s.

  Keep in mind that it is very difficult to see a 300 to 1000 s periodic 
signal with a
  velocity sensor.  It is equivalent to trying to look at a very low 
frequency signal
  with an oscilloscope using a.c. coupling.  Only d.c. coupling (position 
sensing) is
  appropriate in this case.

          There is a dramatic difference between the forcing functions of 
tilt as
  contrasted with horizontal ground acceleration. The tilt response is 
independent of
  frequency, whereas the response to earthquakes (horizontal acceleration 
devoid of
  significant eigenmode oscillatory components) is the classic response 
given by John
  Lahr at the following website:
  http://jclahr.com/science/psn/response/index.html

      If you look at John's six transfer function plots provided at
  http://jclahr.com/science/psn/response/plots.jpg
  it is the right-most pair (response to acceleration) that 'summarize the 
physics' of
  how a seismometer operates.  Yes, one can configure an instrument to plot 
data
  according to any one of the six possibilities John has indicated, but the 
response to
  acceleration is what 'tells the story' of performance.  For frequencies 
above the
  natural frequency of the pendulum, a velocity sensor will always 
outperform a
  velocity sensor.  On the other hand, for frequencies below the natural 
frequency, a
  position sensor will always outperform a velocity sensor (all things 
otherwise
  identical).

        I don't know about you, but I'm not particularly interested in 
frequencies
  above 1 Hz.  Our Volksmeter easily picks up dynamite blasts and other 
local
  disturbances that are nearly always manmade.  Because the earth is so 
large, motions
  it exhibits in response to dynamic changes (earthquakes, tidal forces, ..) 
are at low
  frequencies (not high).

         At low frequencies where everybody seems increasingly interested in 
going
  (reason for bandwidth extension) there is no question of the superiority 
of position
  sensing over velocity sensing.  Why this obvious fact is so muddled in the 
minds of
  so many is a great mystery to me.  Maybe it's because even classical 
physics is
  difficult for most everybody to understand.

        I have placed a paper on my webpage which speaks to this matter, 
titled
  'Seismometer design based on a simple theory of instrument-generated noise 
equivalent
  power:
  http://physics.mercer.edu/hpage/inep/inep.html

         For those of you who want to 'escape the rut' of velocity detection 
that has
  held folks captive for way too long-Larry and my other business partner, 
Les LaZar
  are positioned to provide you with reasonably-priced essential components 
to build
  your own version of the VolksMeter.  Probably most of you will prefer to 
do this
  rather than pay the present $1000 'turnkey' price for our single-pendulum 
instrument.

       I want to point out something that is the result of recently 
discovered
  physics-why small-mass instruments don't perform well.  Although 
conventional wisdom
  says that it's because of Brownian motion (larger for smaller masses), 
this is not
  really the culprit.  The performance limitation is really the result of 
internal
  friction problems that science is only beginning to understand.  The 
smaller the
  seismic mass, the smaller the spring that supports it.  The smaller the 
spring, the
  more significant is the internal friction associated with the 'snap, 
crackle, pop' of
  defect structural changes in the spring (processes that operate at the 
mesoscale).
  For decades we've recognized the all-important properties of defects in
  semiconductors (basis for p and n material of which devices are made), but 
until
  recently very little was understood concerning the importance of defects 
to internal
  friction that regulates the low-frequency performance of seismometers.

        The influence of defects is worse in instruments with springs than 
in those
  that use a pendulum, which is more inherently stable.  Until better 
electronics came
  along, we were stuck with trying to improve low-frequency performance by 
going to
  lower natural frequencies of the mechanical oscillator.  That is no longer 
the only
  viable solution.  Although the pendulum lost favor years ago, it is making 
a
  comeback.  The success of the Shackleford-Gunderson approach should have 
been a cue
  to many that the pendulum needed to be revisited.  With the digital 
electronics of
  the AD7745 there are some advantages that did not exist when the S-G 
instrument was
  developed around its analog circuitry.  For example, the noise of the 
Volksmeter
  electronics does not increase as rapidly with frequency-decrease as is 
true of analog
  circuitry (commercial standard in seismometry being synchronous 
detection).

  Dr. Randall Peters



  __________________________________________________________

  Public Seismic Network Mailing List (PSN-L)

  To leave this list email PSN-L-REQUEST@.............. with
  the body of the message (first line only): unsubscribe
  See http://www.seismicnet.com/maillist.html for more information.







Myself, being new to the hobby, I would like more information about =
this=20
"Volksmeter" devise described in this letter.  Where may I find =
more,=20
photos and etc.
 
Regards,
Jerry
 

  
----- Original Message ----- 
  From:=20
  Larry=20
  Cochrane 
  
To: psn-l@.............. 
  
Sent: Wednesday, December 06, =
2006 3:50=20
  AM
  
Subject: Simple pendulum =
response
  

Hi Everyone,

Dr. Randall Peters asked me to =
forward the=20
  following message to the list.

Regards,
Larry =
Cochrane
Redwood=20
  City, PSN

I've been following with interest the discussions =
concerning=20
  instrument 
characteristics.  Now that my schedule is easing =
somewhat,=20
  I felt that I should get 
involved.  Should it happen that any =
of you=20
  respond to these comments and don't hear 
back from me for a while, =
it's=20
  because I will be away for about a week to the Amer. 
Geophys. =
Union Fall=20
  Conference in San Francisco (starting 11 Dec.). There I will give =

a 15=20
  minute oral presentation titled "State of the art Digital Seismograph" =
.. =20
  The 
abstract is posted at
http://www.agu.org/cgi-bin/sessions5?meeting=3Dfm06=
&part=3DS14B&maxhits=3D400

The=20
  instrument which will be described (and also demonstrated at one of =
the=20
  booths) 
uses a "simple" compound pendulum with a natural frequency =
of 0.92=20
  Hz.  It employs my 
fully differential capacitive detector as =
a=20
  displacement sensor (array form), with 
electronics based in Analog =

  Devices' new award winning capacitance to digital 
converter =
integrated=20
  circuit (AD7745).  Kudo's to our own Larry Cochrane as the =

brains=20
  behind all of (i) the electronics hardware necessary to do the I2C =
logic=20
  
operations required of the chip, and (ii) the software operating =
system in=20
  the form 
of WinSDR and WinQuake.

     =
For those=20
  of you who have been monitoring Larry's instruments at
http://seismicnet.com/quakes=
/images
 =20
  you may have noticed two real-time helicord records generated by the=20
  
single-pendulum instrument (N-S orientation) that he placed =
online. =20
  The 
raw-data-train is lctst.gif, which has been high-pass filtered =
(corner=20
  frequency of 
10 mHz) before display.  The unfiltered waveform =
is=20
  available via download upon 
request from Larry.  This lctst =
is best=20
  suited to the real-time display of 
earthquakes local to the =
Redwood City,=20
  CA site.

      For registering =
teleseismic=20
  earthquakes real-time, Larry has also provided 
lctst1.gif, which =
is the=20
  numerical integration of lctst after first doing a high-pass =

filter. =20
  This operation on the VolksMeter's output provides a display similar =
to what=20
  
is provided by 'bandwidth extension' using electronic means in =
other=20
  instruments such 
as =
geophones.

      =20
  I was pleased to see John Lahr provide links on his webpage describing =
(i)=20
  
transfer function differences between velocity and position =
sensing, and=20
  (ii) 
discussion of the zero-length spring that was invented by =
physicist=20
  Lucien LaCoste in 
the early part of last=20
  century.

      There are some things =
that need=20
  seriously to be clarified concerning theory of 
seismometers, since =
there=20
  is so much confusion; not only among amateur seismologists, 
but =
also even=20
  many professional geoscientists.  Ultimately, the ONLY source of=20
  
seismograph excitation (no matter the instrument design) is =
ENERGY. =20
  Additionally, 
the ONLY thing that delivers energy to the =
seismometer is=20
  Earth's ACCELERATION at the 
site of the instrument.  This is =
true not=20
  only for the instrument's response to 
earthquake waves whose =
periods are=20
  shorter than about 300 s, but also for earth 'hum' 
in which the =
instrument=20
  responds mainly to tilt, when the periods are greater than 
about =
300 to=20
  1000 s.

Keep in mind that it is very difficult to see a 300 to =
1000 s=20
  periodic signal with a 
velocity sensor.  It is equivalent to =
trying=20
  to look at a very low frequency signal 
with an oscilloscope using =
a.c.=20
  coupling.  Only d.c. coupling (position sensing) is =

appropriate in=20
  this case.

        There is =
a=20
  dramatic difference between the forcing functions of tilt as =

contrasted=20
  with horizontal ground acceleration. The tilt response is independent =
of=20
  
frequency, whereas the response to earthquakes (horizontal =
acceleration=20
  devoid of 
significant eigenmode oscillatory components) is the =
classic=20
  response given by John 
Lahr at the following website:
http://jclahr.=
com/science/psn/response/index.html

   =20
  If you look at John's six transfer function plots provided at 
http://jclahr.c=
om/science/psn/response/plots.jpg
it=20
  is the right-most pair (response to acceleration) that 'summarize the =
physics'=20
  of 
how a seismometer operates.  Yes, one can configure an =
instrument=20
  to plot data 
according to any one of the six possibilities John =
has=20
  indicated, but the response to 
acceleration is what 'tells the =
story' of=20
  performance.  For frequencies above the 
natural frequency of =
the=20
  pendulum, a velocity sensor will always outperform a 
velocity=20
  sensor.  On the other hand, for frequencies below the natural =
frequency,=20
  a 
position sensor will always outperform a velocity sensor (all =
things=20
  otherwise 
identical).

      I =
don't know=20
  about you, but I'm not particularly interested in frequencies =

above 1=20
  Hz.  Our Volksmeter easily picks up dynamite blasts and other =
local=20
  
disturbances that are nearly always manmade.  Because the =
earth is so=20
  large, motions 
it exhibits in response to dynamic changes =
(earthquakes,=20
  tidal forces, ..) are at low 
frequencies (not=20
  high).

       At low frequencies =
where=20
  everybody seems increasingly interested in going 
(reason for =
bandwidth=20
  extension) there is no question of the superiority of position =

sensing=20
  over velocity sensing.  Why this obvious fact is so muddled in =
the minds=20
  of 
so many is a great mystery to me.  Maybe it's because even =

  classical physics is 
difficult for most everybody to=20
  understand.

      I have placed a =
paper on my=20
  webpage which speaks to this matter, titled 
'Seismometer design =
based on a=20
  simple theory of instrument-generated noise equivalent =

power:
http://physics.me=
rcer.edu/hpage/inep/inep.html

     &n=
bsp;=20
  For those of you who want to 'escape the rut' of velocity detection =
that has=20
  
held folks captive for way too long-Larry and my other business =
partner,=20
  Les LaZar 
are positioned to provide you with reasonably-priced =
essential=20
  components to build 
your own version of the VolksMeter.  =
Probably=20
  most of you will prefer to do this 
rather than pay the present =
$1000=20
  'turnkey' price for our single-pendulum=20
  instrument.

     I want to point out =
something that=20
  is the result of recently discovered 
physics-why small-mass =
instruments=20
  don't perform well.  Although conventional wisdom 
says that =
it's=20
  because of Brownian motion (larger for smaller masses), this is not =

really=20
  the culprit.  The performance limitation is really the result of =
internal=20
  
friction problems that science is only beginning to =
understand.  The=20
  smaller the 
seismic mass, the smaller the spring that supports =
it. =20
  The smaller the spring, the 
more significant is the internal =
friction=20
  associated with the 'snap, crackle, pop' of 
defect structural =
changes in=20
  the spring (processes that operate at the mesoscale). 
For decades =
we've=20
  recognized the all-important properties of defects in =

semiconductors=20
  (basis for p and n material of which devices are made), but until =

recently=20
  very little was understood concerning the importance of defects to =
internal=20
  
friction that regulates the low-frequency performance of=20
  seismometers.

      The influence of =
defects=20
  is worse in instruments with springs than in those 
that use a =
pendulum,=20
  which is more inherently stable.  Until better electronics came=20
  
along, we were stuck with trying to improve low-frequency =
performance by=20
  going to 
lower natural frequencies of the mechanical =
oscillator. =20
  That is no longer the only 
viable solution.  Although the =
pendulum=20
  lost favor years ago, it is making a 
comeback.  The success =
of the=20
  Shackleford-Gunderson approach should have been a cue 
to many that =
the=20
  pendulum needed to be revisited.  With the digital electronics of =

the=20
  AD7745 there are some advantages that did not exist when the S-G =
instrument=20
  was 
developed around its analog circuitry.  For example, the =
noise of=20
  the Volksmeter 
electronics does not increase as rapidly with=20
  frequency-decrease as is true of analog 
circuitry (commercial =
standard in=20
  seismometry being synchronous detection).

Dr. Randall=20
  =
Peters



___________________________________________________=
_______

Public=20
  Seismic Network Mailing List (PSN-L)

To leave this list email =
PSN-L-REQUEST@...............
=20
  with 
the body of the message (first line only): unsubscribe
See =
http://www.seismicnet.co=
m/maillist.html=20
  for more information.