Good work Chris on the approximation of tilt in the garden gate style =
seismometers.  I attempted this calculation once upon a time by =
installing a turnbuckle in the support wire--raising the mass till it =
was unstable, then a half turn or more backwards would bring the period =
to 18 sec. and stability.
   I achieved better results from using .005 and.010 in. sheet metal =
shims under the "front" single support of the tripod base.  I started at =
10 sec, added shims carefully till instability, and then removed shims =
to the desired period.  The thickness of the shims removed gave an idea =
of tilt, which I converted to approximately 0.5 degree.
        Keep up the good work in amateur seismology-- Jim Lehman
  ----- Original Message -----=20
  From: ChrisAtUpw@..........
  To: psn-l@.................
  Sent: Sunday, May 31, 2009 9:13 PM
  Subject: Re: Level of garden gate style horizontal seismometers


  In a message dated 30/05/2009, gmvoeth@........... writes:
    Just out of curiosity has any of you guys with those garden gate =
seismometers ever put one of these little plastic levels on the lever to =
see just how far off level it is at 10 or 20 seconds. I mean ere like =
1/2, 1/4 or so a bubble across the line if you understand what I mean =
here ?
  Hi Geoff,

      My 9" spirit level shows ~1.5 deg change when the bubble moves by =
it's own length.=20
      The tilt angle of a 1.5 second arm extended to 20 seconds is 0.32 =
Degrees.

      Regards,

      Chris Chapman









Good work Chris on the approximation of tilt in the garden gate =
style=20
seismometers.  I attempted this calculation once upon a time by =
installing=20
a turnbuckle in the support wire--raising the mass till it was unstable, =
then a=20
half turn or more backwards would bring the period to 18 sec. =
and=20
stability.
   I achieved better results from using .005 and.010 =
in.=20
sheet metal shims under the "front" single support of the tripod =
base.  I=20
started at 10 sec, added shims carefully till instability, and then =
removed=20
shims to the desired period.  The thickness of the shims removed =
gave an=20
idea of tilt, which I converted to approximately 0.5 degree.
        Keep up the good work in =
amateur=20
seismology-- Jim Lehman

  
----- Original Message ----- 
  From:=20
  ChrisAtUpw@....... 
  
To: psn-l@.............. 
  
Sent: Sunday, May 31, 2009 9:13 =
PM
  
Subject: Re: Level of garden =
gate style=20
  horizontal seismometers
  


  
In a message dated 30/05/2009, gmvoeth@........... =
writes:
  Just=20
    out of curiosity has any of you guys with those garden gate =
seismometers=20
    ever put one of these little plastic levels on the lever to see just =
how far=20
    off level it is at 10 or 20 seconds. I mean ere like 1/2, 1/4 or so =
a bubble=20
    across the line if you understand what I mean here =
?
  
Hi Geoff,
  
 
  
    My 9" spirit level shows ~1.5 deg =
change when=20
  the bubble moves by it's own length. 
  
    The tilt angle of a 1.5 second arm =
extended to=20
  20 seconds is 0.32 Degrees.
  
 
  
    Regards,
  
 
  
    Chris Chapman