PSN-L Email List Message

Subject: Re: Lehman help
From: JIm Hannon jmhannon@........
Date: Sun, 09 Jan 2000 19:49:53 -0600


> Gentlemen,
> I am experiencing rather frustrating problems in getting my Lehman set up.
> I just finished the construction,  and am now trying to get the boom to
> center.  The boom is setup so that it has a VERY slight downward slant from
> level.  I have leveled the base plate and it seems that no matter what I do
> to the leveling screws, the boom either performs a major swing to either the
> right or left. It takes almost NO turning of the leveling screw and the boom
> will go from a center of about 30 degrees to the right, to a center that is
> about the same except to the left.  It seems as though I just can't get the
> darn thing to center up.
> I know a lot of you out there have built the Lehman,  so I'm hoping that
> maybe someone can give me some assistance.
> Please help if you can....
> Jim D. Martin
> New Haven, Indiana

The important tilt is the position of the upper and lower pivot points with
respect to vertical. The action you describe is consistant with the upper pivot
point being further from the mass in the horizontal direction than the lower
pivot point. The angle of the boom itself is not particulary important. You
should be able to use the leveling screws to adjust out your problem by lowering
the mass end of the instrument. Then you can adjust the screws for tilt right or
left to center the mass. There are actually two different adjustments made with
the leveling screws. The centering which you are trying to do, and the period
adjustment which you now have set to somewhere beyond infinite. Lowering the
mass end of the instrument will decrease the period.
Jim Hannon


Public Seismic Network Mailing List (PSN-L)

[ Top ] [ Back ] [ Home Page ]

Larry Cochrane <cochrane@..............>