Hi Chris,  I did double check everything, and the sensor seems to be =
working just fine.

The reason I know it is missing earthquakes is that I am running three =
channels, One vertical spring, one tiltmeter, and one =
Lehman..........The Lehman misses a lot of events the other two record.

Yes I think part of it is directional.

Would you think this could account for it..............The Lehman is set =
for twenty seconds, but at twenty seconds, I think it is maxed out, that =
is to say,  I don't think I could get 21 seconds.
Even 20 seconds, for this unit, may be too much.   I say that because it =
drifts, sometimes falling 1/2" per week to the left or to the right.  I =
adjust it back to  center and it stays only for a few days.

Might it simply be this unit is not capable of working at 20 seconds.   =
The sticking you mentioned.........could this be because it is =
overextended, perhaps this machine is only capable of a WORKING PERIOD =
of 15 seconds????

When I set it to 20, and move the boom, it does go to center, but =
because of the drift issue, it may not be capable of HOLDING CENTER. and =
perhaps this is stopping its sensitivity to all but the larger =
earthquakes????

On the good side the events it does record, 6.2 Alaska and 7.8 China, =
look really good.    Thanks for your help.
Ted
  ----- Original Message -----=20
  From: ChrisAtUpw@..........
  To: psn-l@.................
  Sent: Monday, May 26, 2008 12:51 PM
  Subject: Re: Adjusting the period


  In a message dated 2008/05/26, tchannel1@............ writes:


    I plan on changing the period from 20 seconds to another number, not =
sure what that number will be.   What I want to see, is how it records =
at different period settings.
    I know the advantages of the 20 seconds.  The disadvantage is it =
misses many other smaller earthquakes.
    My question:  Before I try other period numbers..........Have you =
tried this, and what were the results?
    I really don't know what the result would be.


  Hi Ted,

         If your Lehman is working properly, it should see all signals =
between the natural resonant period, at say 20 seconds and the low pass =
fiolter of your amplifier at 10 Hz.

         If you set the period to 10 seconds, it will only record =
signals between 10 seconds and 10 Hz. It will have about 1/4 theprevious =
sensitivity to 20 second Love waves.=20

         You WILL NOT see any more Earthquakes this way.

         Remember that Lehmans are directional? Could this be why you =
are missing some quakes? What quakes have you missed and why do you =
think you should have recorded them?
         An alternative is that your suspension may be sticking and =
preventing the arm from moving freely. You may then only see larger =
quakes.
         Can you remind me what suspensions, top and bottom, you are =
using, please?
         Do you see the normal 4 to 8 second microseisms OK?

         Regards,








Hi Chris,  I did double check =
everything, and=20
the sensor seems to be working just fine.
 
The reason I know it is missing =
earthquakes is that=20
I am running three channels, One vertical spring, one tiltmeter, and one =

Lehman..........The Lehman misses a lot of events the other two=20
record.
 
Yes I think part of it is =
directional.
 
Would you think this could account for=20
it..............The Lehman is set for twenty seconds, but at twenty =
seconds, I=20
think it is maxed out, that is to say,  I don't think I could get =
21=20
seconds.
Even 20 seconds, for this unit, may be =
too=20
much.   I say that because it drifts, sometimes falling 1/2" =
per week=20
to the left or to the right.  I adjust it back to  center and =
it stays=20
only for a few days.
 
Might it simply be this unit is not =
capable of=20
working at 20 seconds.   The sticking you =
mentioned.........could this=20
be because it is overextended, perhaps this machine is only capable of a =
WORKING=20
PERIOD of 15 seconds????
 
When I set it to 20, and move the boom, =
it does go=20
to center, but because of the drift issue, it may not be capable of =
HOLDING=20
CENTER. and perhaps this is stopping its sensitivity to all but the =
larger=20
earthquakes????
 
On the good side the events it does =
record, 6.2=20
Alaska and 7.8 China, look really good.    Thanks for =
your=20
help.
Ted

  
----- Original Message ----- 
  From:=20
  ChrisAtUpw@....... 
  
To: psn-l@.............. 
  
Sent: Monday, May 26, 2008 =
12:51 PM
  
Subject: Re: Adjusting the =
period
  

In a=20
  message dated 2008/05/26, tchannel1@............=20
writes:


  I plan on changing the period from 20 seconds to another =
number,=20
    not sure what that number will be.   What I want to see, =
is how it=20
    records at different period settings.
I know the =
advantages of the=20
    20 seconds.  The disadvantage is it misses many other smaller=20
    earthquakes.
My question:  Before I try other period=20
    numbers..........Have you tried this, and what were the =
results?
I really don't =
know what the=20
    result would be.

Hi=20
  Ted,

       If your Lehman is =
working=20
  properly, it should see all signals between the natural resonant =
period, at=20
  say 20 seconds and the low pass fiolter of your amplifier at 10=20
  Hz.

       If you set the period =
to 10=20
  seconds, it will only record signals between 10 seconds and 10 Hz. It =
will=20
  have about 1/4 theprevious sensitivity to 20 second Love waves.=20
  

       You WILL NOT see any more =

  Earthquakes this way.

       =
Remember=20
  that Lehmans are directional? Could this be why you are missing some =
quakes?=20
  What quakes have you missed and why do you think you should have =
recorded=20
  them?
       An alternative is that =
your=20
  suspension may be sticking and preventing the arm from moving freely. =
You may=20
  then only see larger quakes.
       =
Can you=20
  remind me what suspensions, top and bottom, you are using,=20
  please?
       Do you see the normal =
4 to 8=20
  second microseisms OK?

      =20
  Regards,

       Chris =
Chapman=20