PSN-L Email List Message

Subject: Re: Large earthquake near cost of Canada
From: "Thomas Dick" dickthomas01@.............
Date: Mon, 7 Jan 2008 19:28:31 -0600

    One setup instruction seems to be missing from the current AS1 manual.

    When you have added load washers to the vertical bolt to level the arm 
for your particular spring / mass combination, you should then dismount the 
arm and hang it ~vertically (without the spring) by a strip of adhesive tape 
from the knife edge / hinge line. You then compare this to a vertical thread 
on a nut / a plumb line. You adjust the arm to hang vertically by moving the 
position of the mass balance washers held between the two clamp nuts. This 
offsets the mass of the red Alnico U magnet on the lower side of the arm.

    If you don't do this, the C of G will not be level with the hinge and 
you can get an appreciable sensitivity to horizontal Love waves.

    As far as I am aware, there is NO comparable method for setting up an 
EQ1 properly.

  Hi Chris, hope you are doing OK with the New Year. The above seems hard... 
at least, to understand why. I didn't have to add any washers.I have been 
disappointed with my AS-1.  It was the first instrument I had commerically 
built. The Lehmans are doing fine; sometimes a little noisier than I'd like. 
The performance of the AS-1 seems to vary---- I got better results from my 
4.5 Hz geophone than on the AS-1 from yesterday's 1.4 mg on the New Madrid 
fault and yet the AS-1 did OK on the Greek quake. During the 2nd Queen 
Charlotte quake, the AS-1 showed little P while more LQ & LR than I 
expected. That is what precipitated my queries to John. I expected P to be 
higher in amplitude in Oregon -- even on the 1.4 mg on the New Madrid, the P 
was larger than the S . His comment about using something other than a razor 
blade edge didn't fall on deft ears...been wondering about that. Got a new 
billfold for have to find some money to put into it...JoAnn has 
reduced my allowance! 

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