Hi Chris,  Thanks for the reply, =20
1   What sort of period have you selected for the pendulum?    I think =
it is 5 to 15 seconds, I am still trying to fine tune it. =20
=20
2  Have you set up the damping to near 0.7 critical?    No damp made =
yet, but hope to use magnets  I know the importance of this but was =
hoping to prove the amp and filter first.

3  2.5 Hz lowpass is on the low side.
  The amp/filter is still on the breadboard so I can change the values,  =
Do you think I should use 10Hz instead of 2.5Hz?
Sorry I don't know how many poles,  It goes from a op amp "the filter" =
into another op amp "the amp" with a gain of 100 I think.
and the output voltage is min. 1.4v and max 7.5 volts. I adjust it to =
2vs Into a A/D Converter DATAQ 194 which requires 0 to 10v.

4  Sorry I don't understand this part.  I am in Idaho hundreds of miles =
from the ocean, could I still see these?
 You get a microseism background from the ocean between 4 and 8 sec, so =
you may want to filter above and below this. Can you take an unfiltered =
trace of background and call up an FFT plot of amplitude versus =
frequency? The ocean background peak should show up clearly. The period =
is a bit different for the west and east coasts. In the middle of the =
USA, you may see two peaks.

Many Thanks, Ted
  ----- Original Message -----=20
  From: ChrisAtUpw@..........
  To: psn-l@.................
  Sent: Wednesday, September 20, 2006 10:26 PM
  Subject: Re: My first Sensor


  In a message dated 21/09/2006, tchannel@.............. writes:
    Hi, I am building a horizontal pendulum sensor, my first attempt.  I =
built my own amp and filter.  I configured the Low pass filter to Low =
pass 2.5Hz.  Before I installed the filter, the sensor would pick up =
footsteps or stomps on the concrete floor, now nothing creates a trace, =
except If I blow on the beam it develops a nice trace.   No earthquakes =
since I installed the filter so I don't know if its going to work.
  Hi Ted,

      I always pays to ask!=20

      What sort of period have you selected for the pendulum? Have you =
set up the damping to near 0.7 critical? Are you using oil or magnetic =
damping?

      1 I could use some advise, if the amp and filter seem to be okay =
or if I have over done something.

       2.5 Hz lowpass is on the low side. It is more common to use 10 Hz =
for quiet locations and maybe 5 Hz for urban sites. The filter actually =
delays the signal passing through it and you want to keep this to less =
than 0.2 sec.=20
      What type of filter are you using and how many poles?

      Teleseismic quakes usually have P waves of about 1 Hz and S waves =
fo about 0.5 Hz. Regional quakes usually have P waves less than 3 Hz, =
but local quakes may have components over 20 Hz. The earth absorbs the =
higher frequencies preferentially. =20
    2  Another issue is, I am overwhelmed with confusion about "Seconds =
vs Hz"  I understand how to work with them and what they mean.  But the =
more I read the more confused I get.  The events come in low =
frequencies, 10 to 20seconds  is that  0.1Hz. and .05Hz?   Does that =
make everything above those Hz, or should I say, below those  periods =
unwanted?   You can see I need help.
      Correct. It is just easier to use 10 sec as opposed to 0.1 Hz.
    3  Using AmaSies, what values do I set the Low pass filter, and what =
values do I set the high pass filter, for enhancing an enlarged detail =
trace?  Do I use both a low and high together.........Some examples =
would be helpful.   The little I have use them has just been trial and =
error, to get the best picture.
      Since you have a real filter at 2.5 Hz, there isn't much point =
setting the lowpass filter above this.You may wish to leave the high =
pass filter unselected. The P and S waves may have quite low amplitudes. =
It is common to pick up the large amplitude Love waves over 10 sec and =
then search back for the P and S waves.=20
      You get a microseism background from the ocean between 4 and 8 =
sec, so you may want to filter above and below this. Can you take an =
unfiltered trace of background and call up an FFT plot of amplitude =
versus frequency? The ocean background peak should show up clearly. The =
period is a bit different for the west and east coasts. In the middle of =
the USA, you may see two peaks.

      Regards,








Hi Chris,  Thanks for the reply,  
1   What sort of period have you selected for the=20
pendulum?    I think it is 5 to 15 seconds, I am still =
trying to=20
fine tune it.  
 
2  Have you set up the damping to near 0.7 =
critical?   =20
No damp made yet, but hope to use magnets  I know the importance of =
this=20
but was hoping to prove the amp and filter first.
 
3  2.5 Hz lowpass is on the low side.
  The amp/filter is still on the breadboard so I can change =
the=20
values,  Do you think I should use 10Hz instead of 2.5Hz?
Sorry I don't know how many poles,  It goes from a op amp "the =
filter"=20
into another op amp "the amp" with a gain of 100 I think.
and the output voltage is min. 1.4v and max 7.5 volts. I =
adjust it to=20
2vs Into a A/D Converter DATAQ 194 which requires 0 to =
10v.
 
4  Sorry I don't understand this part.  I am in Idaho =
hundreds of=20
miles from the ocean, could I still see these?
 You get a microseism background from the ocean between 4 and =
8 sec,=20
so you may want to filter above and below this. Can you take an =
unfiltered trace=20
of background and call up an FFT plot of amplitude versus frequency? The =
ocean=20
background peak should show up clearly. The period is a bit different =
for the=20
west and east coasts. In the middle of the USA, you may see two =
peaks.
 
Many Thanks, Ted

  
----- Original Message ----- 
  From:=20
  ChrisAtUpw@....... 
  
To: psn-l@.............. 
  
Sent: Wednesday, September 20, =
2006 10:26=20
  PM
  
Subject: Re: My first =
Sensor
  


  
In a message dated 21/09/2006, tchannel@..............=20
writes:
  
    
Hi, I am building a horizontal =
pendulum sensor,=20
    my first attempt.  I built my own amp and filter.  I =
configured=20
    the Low pass filter to Low pass 2.5Hz.  Before I installed the =
filter,=20
    the sensor would pick up footsteps or stomps on the concrete floor, =
now=20
    nothing creates a trace, except =
If I blow on=20
    the beam it develops a nice trace.   No earthquakes since =
I=20
    installed the filter so I don't know if its going to=20
    work.
  
Hi Ted,
  
 
  
    I always pays to ask! 
  
 
  
    What sort of period have you selected for =
the=20
  pendulum? Have you set up the damping to near 0.7 critical? Are you =
using oil=20
  or magnetic damping?
  
 
  
    1 I could =
use some advise,=20
  if the amp and filter seem to be okay or if I have over done=20
  something.
  
 
  
     2.5 Hz lowpass is on the low =
side. It=20
  is more common to use 10 Hz for quiet locations and maybe 5 Hz for =
urban=20
  sites. The filter actually delays the signal passing through it =
and you=20
  want to keep this to less than 0.2 sec.=20
  
    What type of filter are you using and how =
many=20
  poles?
  
 
  
    Teleseismic quakes usually have P waves =
of about=20
  1 Hz and S waves fo about 0.5 Hz. Regional quakes usually have P waves =
less=20
  than 3 Hz, but local quakes may have components over 20 Hz. The earth=20
  absorbs the higher frequencies =
preferentially.  
  
    
2  Another issue is, I am =
overwhelmed with=20
    confusion about "Seconds vs Hz"  I understand how to work with =
them and=20
    what they mean.  But the =
more I read the=20
    more confused I get.  The events come in low frequencies, 10 to =

    20seconds  is that  0.1Hz. and .05Hz?   Does =
that make=20
    everything above those Hz, or should I say, below those =
 periods=20
    unwanted?   You can see I need=20
help.
  
    Correct. It is just easier to use 10 sec =
as=20
  opposed to 0.1 Hz.
  
    
3  Using AmaSies, what values =
do I set the=20
    Low pass filter, and what values do I set the high pass filter, for=20
    enhancing an enlarged detail trace?  Do I use both a low and =
high=20
    together.........Some examples would be helpful.   The =
little I=20
    have use them has just been trial and error, to get the best=20
    picture.
  

  
    Since you have a real filter at 2.5 Hz, =
there=20
  isn't much point setting the lowpass filter above this.You may wish to =
leave=20
  the high pass filter unselected. The P and S waves may have quite low=20
  amplitudes. It is common to pick up the large amplitude Love =
waves over=20
  10 sec and then search back for the P and S waves. 
  
    You get a microseism background from the =
ocean=20
  between 4 and 8 sec, so you may want to filter above and below this. =
Can you=20
  take an unfiltered trace of background and call up an FFT plot of =
amplitude=20
  versus frequency? The ocean background peak should show up clearly. =
The period=20
  is a bit different for the west and east coasts. In the middle of the =
USA, you=20
  may see two peaks.
  
 
  
    Regards,
  
 
  
    Chris=20
Chapman