PSN-L Email List Message

Subject: Re: Lehman construction
From: twleiper@........
Date: Thu, 13 Jan 2000 04:18:38 -0500

On Wed, 12 Jan 2000 22:22:23 +0000 n0cwr@......... writes:
>Our Lehman is in a room off the garage.
>Two cars in the garage great...
>Fine with one car in the garage but, 
>if I attain too high of a period (16 sec plus) with both cars
>out of the garage the boom rolls over to the side - flatline till
>ones back! 12 - 16 second period = no problems. 

My daughter's Lehman is on a pier cast atop what is either an immovable
huge bolder or exposed bedrock in the root / wine cellar. It is a very
stable environment with natural temperature control and the seismo is
made from thermally stable materials, such as a granite tool and die
makers slab for a base. With a natural period of 50 seconds it only needs
seasonal centering adjustment for what I theorize is increased weight of
the frame house (the foundation rests on said bolder about 15 feet away)
due to higher relative humidity in the summer, or the presence of leaves
on a rather large beach tree about 30 feet away. My wife will not let us
cut the tree down to see... 

With this level of sensitivity I can not only tell when the oil truck
backs into the driveway (about 75 ft away), but I can also tell whether I
am at the beginning or the end of his run based on the weight of the
truck. When the truck is empty I have to know he is there to pick out the
offset in the six second noise level, but full is a clear LP tilt event
of about 8 times the background amplitude. He is a friend of mine and I
have verified it. 

So is the insanity worth it? Not really. Only in the case of the most
distant surface waves have we been able to see higher performance than
with her original unit
( running end to end,
and in no case did it detect anything that was not discernable on the
"science fair unit". That first unit is no slouch and can be adjusted to
about a 40 second period, but dimensional instability and perhaps
magnetometry effects of the suspended magnet design limit the "seasonally
adjusted" period to about 15 to 18 seconds. It can only see the oil truck
when it is full.

So here is the challenge question: 

Assuming identical detector,gain and filtration (they are) and only the
difference in period, can you calculate the capacity of the oil truck?
(ST, Give everybody else a day before posting the correct answer,


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