## PSN-L Email List Message

Subject: Re: Incresing the period of a lehmans seismomter ?
From: ChrisAtUpw@.......
Date: Sat, 9 May 2009 23:44:13 EDT

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In a message dated 10/05/2009, shammon1@............. writes:

Try  using a bubble level to know when the boom is level. Then tilt the end
of the  boom down, never up. I normally start by using a level to make sure
the  vertical upright is at zero degrees and then I level the boom. I then
add  about 1-5 degree of tilt in the upper most point of the upright in the
direction of the boom. I have three level screws the base plate and a
machine  screw in the end of the boom to make the adjustment.
Regards, Stve Hammond

Hi Steve,

The period is not effected by the angle of the boom  itself. It is the
angle between the local vertical and the line joining the two  centres of
rotation which is critical for determining the period.

In
_http://jclahr.com/science/psn/chapman/2008%20lehman/lehman_prototype.jpg_
(http://jclahr.com/science/psn/chapman/2008%20lehman/lehman_prototype.jpg)  this  line joins the centre of the 1/2" ball bearing on the upright
with  the fine wire at the top where it is clamped by the edges of the brass
variable rotating clamp washers. The horizontal arm is set up parallel to
the  base bar just for convenience.

Regards,

Chris Chapman

In a message dated 10/05/2009, shammon1@............. writes:
Try
using a bubble level to know when the boom is level. Then tilt the end=
of the
boom down, never up. I normally start by using a level to make sure the=

vertical upright is at zero degrees and then I level the boom. I then ad=
d
about 1-5 degree of tilt in the upper most point of the upright in=
the
direction of the boom. I have three level screws the base plate and a ma=
chine
screw in the end of the boom to make the adjustment. Regards, Stve=
Hammond

Hi Steve,

The period is not effected by the angle of th=
e boom
itself. It is the angle between the local vertical and the line joining th=
e two
centres of rotation which is critical for determining the period.

In http://jclahr.com/science/psn/chapman/2008%20lehman/lehman_prototy=
pe.jpg this
line joins the centre of the 1/2" ball bearing on the upright with
the fine wire at the top where it is clamped by the edges of the=
brass
variable rotating clamp washers. The horizontal arm is set up parallel to=
the
base bar just for convenience.

Regards,

Chris Chapman
```