PSN-L Email List Message

Subject: Re: Horizontal Pendulum]
From: "Connie and Jim Lehman" lehmancj@...........
Date: Sat, 22 Oct 2005 10:43:03 -0400

Geoffery--Thanks for your interest in seismology and the "Lehman horizontal"
design.  I am puzzled a bit by your use of "shims"-- my idea of shims has
been only in work demanding small changes in distance--like leveling a
table, or a piece of scientific apparatus.  The usual shims in precision
work are sheets of metal with so many l/1000ths of an inch in
thickness--otherwise known as mills} Since the seismo base is a tripod--
(for stability)  shim material can be used to balance and level the system.
  I am not sure what version of sensor plans you are following, but I
suggest that you keep construction simple with a wire hinge at the top, and
a knife edge on the boom end.  After you get that working with a 15-20 sec
free swing, properly damped, you can refine and modify your design as you
like.  To get a good "garden gate" swing the upper wire hinge (tensional)
should be about 1/4th inch off the vertical with the compressional knife
   Best wishes,   Jim

----- Original Message -----
From: "Larry Cochrane" 
Sent: Saturday, October 22, 2005 2:36 AM
Subject: [Fwd: Horizontal Pendulum]

> -------- Original Message --------
> Subject: Horizontal Pendulum
> Date: Fri, 21 Oct 2005 20:33:15 -0400
> To: Larry Cochrane 
> Larry, thank you for your reply. The PSN-L@............... did not work.
(i don't
> have good computer skills.) Would you post this on the list? i'm new to
the list and
> seismology. i've enjoying reading the posts and have been thinking about a
> pendulum Lehman type seismo using metal shims (what is the best material
for shims
> and best thickness?)    Anyway, the horizontal pendulum would be supported
by shims
> above and below the pendulum that are ninety degrees perpendicular to the
> axis of the pendulum.  The upper shim would be attached to the 'mast'  and
then to a
> tube or rod that is attached to the pendulum, again with the linear axis
will be
> perpendicular to the pendulum's horizontal plane.  This would place the
upper shim in
> tension. The lower shim is also placed in tension by attaching the end
away from the
> coil to the above mentioned tube or pipe that is attached to the pendulum.
The lower
> shim will run away from the mast towards the coil. One thing that will
have to be
> determined is the position were the upper and lower tubes join the
pendulum. The
> tubes' positions would determine the flex positon of the shims, hopefully
to be able
> to find the point of greatest flexion of the shims with the lowest torque
needed to
> cause the flex or bending of the shim. Have many people tried this? How
did it work?
> Thanks, geofffrey roberts, Crystal River, Florida
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