## PSN-L Email List Message

Subject: Re: Level of garden gate style horizontal seismometers
From: "Jim and Connie Lehman" lehmancj@...........
Date: Mon, 1 Jun 2009 11:06:10 -0400

```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

```

[ Top ] [ Back ] [ Home Page ]