Hi Chris,   A few questions:

1 Does your coil and damper assemblies just set on the aluminum base, =
free to move for adjustment, or are they fixed to the base?

2 You cleaned the plates, which hold the magnets, and then painted the =
exterior, but not the surface the magnets touch.  Would the paint =
interfere with something on that surface?

3 This is a hard question.  Assuming I have finished my sensor, and =
leveled it, what is the procedure for adjusting the period?  I know the =
target angle.
I would guess one would have to start at that point, with the base =
level, the pendulum level, and everything plumb.
You mentioned the formula for determining the angle of the hinge, I have =
that information.  Not knowing the correct procedure, and not being able =
to measure that small of an angle, I would have converted the angle into =
a decimal of inches, and measured the difference from the top hinge to =
the bottom hinge.  Maybe you could walk me through this procedure?

4 I get confused with many of these terms, so I hope you understand this =
question.  If the target period is say 10 seconds, would the arm move, =
when pulled 10mm, verrrrrrrrrry slowly, taking 10 seconds to complete =
one cycle?

5  After it is leveled and the period is set, Is it then that you can =
check the damp, by moving the arm 10mm and releasing it?
I know what an underdamped situation would look like.  But is there way =
to tell if it is over damped?

Thanks, Ted




  ----- Original Message -----=20
  From: ChrisAtUpw@..........
  To: psn-l@.................
  Sent: Tuesday, October 03, 2006 9:23 PM
  Subject: Re: Building a lehman seismometer


  In a message dated 2006/10/04, jonfr500@......... writes:


    I also plan to build a Lehman seismometer, if I can keep it small =
enough. But I need a suggestion for material and some mesurements and =
proper drawings before I can start. I also want to keep the frequency of =
the Lehman seismometer around 1Hz.


  Hi Jon,=20

         The  whole point about a Lehman type seismometer is that you =
take a pedulum which would have a period of about 1.3 to 1.5 sec if =
mounted vertically and extend the period to maybe 20 sec. The sensor =
will respond from 20 sec to the 10 Hz of your amplifier filter. I =
suspect that an arm of between 45 and 60 cm would be fine for you. Don't =
try to make it smaller. This should pick up your seismic signals very =
well.

         I make a T / L frame with U channel Al with 5 mm Al plate for =
the corner supports. I don't know what materials are available to you. =
You can use 50 x 25 mm, but I prefer 75 x 25 mm section.

         Regards,








Hi Chris,   A few =
questions:
 
1 Does your coil and damper =
assemblies just=20
set on the aluminum base, free to move for adjustment, or are they fixed =
to the=20
base?
 
2 You cleaned the plates, which =
hold the=20
magnets, and then painted the exterior, but not the surface the magnets=20
touch.  Would the paint interfere with something on that=20
surface?
 
3 This is a hard question.  =
Assuming I=20
have finished my sensor, and leveled it, what is the procedure for =
adjusting the=20
period?  I know the target angle.
I would guess one would have to start =
at that=20
point, with the base level, the pendulum level, and everything=20
plumb.
You mentioned the formula for =
determining the angle=20
of the hinge, I have that information.  Not knowing the correct =
procedure,=20
and not being able to measure that small of an angle, I would have =
converted the=20
angle into a decimal of inches, and measured the difference from the top =
hinge=20
to the bottom hinge.  Maybe you could walk me through this=20
procedure?
 
4 I =
get confused=20
with many of these terms, so I hope you understand this question.  =
If the=20
target period is say 10 seconds, would the arm move, when pulled 10mm,=20
verrrrrrrrrry slowly, taking 10 seconds to complete one =
cycle?
 
5  After it is leveled and the =
period is set,=20
Is it then that you can check the damp, by moving the arm 10mm and =
releasing=20
it?
I know what an underdamped situation =
would look=20
like.  But is there way to tell if it is over damped?
 
Thanks, Ted
 
 
 
 

  
----- Original Message ----- 
  From:=20
  ChrisAtUpw@....... 
  
To: psn-l@.............. 
  
Sent: Tuesday, October 03, 2006 =
9:23=20
  PM
  
Subject: Re: Building a lehman=20
  seismometer
  

In a=20
  message dated 2006/10/04, jonfr500@......... =
writes:


  I also plan to build a Lehman seismometer, if I can keep =
it=20
    small enough. But I need a suggestion for material and some =
mesurements and=20
    proper drawings before I can start. I also want to keep the =
frequency of the=20
    Lehman seismometer around 1Hz.

Hi Jon,=20
  

       The  whole point =
about a=20
  Lehman type seismometer is that you take a pedulum which would have a =
period=20
  of about 1.3 to 1.5 sec if mounted vertically and extend the period to =
maybe=20
  20 sec. The sensor will respond from 20 sec to the 10 Hz of your =
amplifier=20
  filter. I suspect that an arm of between 45 and 60 cm would be fine =
for you.=20
  Don't try to make it smaller. This should pick up your seismic signals =
very=20
  well.

       I make a T / L frame =
with U=20
  channel Al with 5 mm Al plate for the corner supports. I don't know =
what=20
  materials are available to you. You can use 50 x 25 mm, but I prefer =
75 x 25=20
  mm section.

      =20
  Regards,

       Chris Chapman=20