PSN-L Email List Message

Subject: Re: more seis feet
From: Mark Robinson other@...............
Date: Tue, 02 Jan 2001 12:19:06 +1300

Hi all

In optical mounts, such as those for the mirrors in an ion laser, there
are some refinements which may be of some use in this application. The
laser application has similar or greater requirements for accuracy and

The principle difference is that the levelling is done between two
pieces that are structural to the instrument, and that these two pieces
are held in tight coupling to each other. At each of the three mounting
points the two plates are held together by suitably strong springs, and
pulled apart by the adjusting screws. In general one point is more or
less fixed, while the other two points provide adjustment in the x and y
dimensions. It would seem natural to put the fixed point under the mast
of a lehman. 

An arrangement of this type would allow the bottom plate to the screwed
firmly to whatever surface the instrument is meant to be measuring, and
the rest of the instrument adjusted relative to this.

a further refinement observable on laser mirror mounts are physical
restraints preventing the moveable plate from being displaced by gross
shocks. a screw with a waskher and a spacer under it's head through a
clearance hole in the adjustable plate, screwed firmly into the base
plate is common.

The springs are usually mounted to bars set in grooves across holes in
both plates. The bearing points are usually ball headed. The fixed point
is commonly a ball bearing set over holes in each plate.

A well engineered arrangement such as this provides excellent coupling
between the instrument and the substrate, as well as fine and repeatable
adjustments. and it should stay very firmly put in even a very large

I hope this is understandable and helpful.

Happy New Year everyone


Public Seismic Network Mailing List (PSN-L)

[ Top ] [ Back ] [ Home Page ]

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