PSN-L Email List Message

Subject: Pivots Re: Incresing the period of a lehmans seismomter ?
From: "Robert O. Green" rog@..........
Date: Tue, 12 May 2009 20:13:11 -0700


Do you have any close up pictures of your upper and lower pivots?


ChrisAtUpw@....... wrote:
> 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 
> 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
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