## PSN-L Email List Message

Subject: Re: more horizontal seis boom angle
From: Jim Hannon jmhannon@........
Date: Thu, 17 Feb 2000 05:58:11 -0600

```At 10:03 PM 2/16/00 -0800, you wrote:
>Sean-Thomas, BTW, I take great interest in your formulas, I find them very
>informative. But I keep coming up with more questions as I think more about
>the problem. For example, where is the end of the boom? In my case, the boom
>is 38 1/4-in long tip to tip. I use a 1/4-copper plate for damping and it
>hang on a L-bracket at the at the end. At the 32-inch point, the upper wire
>intersects the boom. The coil and magnet are mounted at the 24 3/4-inch
>point. So in your equation, L=which point? The end of the boom or the
>intersection point where the guide wire is mounted?
>Regards, Steve Hammond  PSN  Aptos, California
>
Steve,
The description of the "end of the boom" make the assumption that there is
a right angle between the line formed by the upper and lower pivot points
and the boom. This mainly just simplifies talking aout the arrangment. The
important parameter is the vertical alignment of upper and lower pivot
points. The line formed by the upper and lower pivot points must tip
slightly toward the end of the boom or the mass. Then if there is a right
angle between the pivot line and the line defined by the boom you can say
that the boom has to be tipped down slightly. How the mass is distributed
at the end of the boom really doesn't make a lot of difference. Talking
about the position of the end of the boom causes some confusion in that it
leads you to think (for example) that by adjusting the length of the
supporting wire you can adjust the period. It may have some effect but the
real adjustment is the angle of the line formed by the pivot points. That
is why the period is adjusted by the leveling screws in the base of the
insrument.
Jim Hannon
http://soli.inav.net/~jmhannon/
42,11.90N,91,39.26W
WB0TXL

_____________________________________________________________________

Public Seismic Network Mailing List (PSN-L)

```