PSN-L Email List Message

Subject: Re: Large earthquake near cost of Canada
From: John Lahr johnjan@........
Date: Mon, 07 Jan 2008 18:54:41 -0800

Hi Thomas,

How does your AS-1 record compare with those posted here:
What is the closest station to you that has a record showing?

When the AS-1 isn't working well the problem is often due to slight 
contact between the magnet and the coil, or between the damping 
washer and the oil container.  Be sure to check these areas.  The 
system will appear to work, as it will respond to your presence 
around the sensor, but it's will not record earthquakes well if there 
is any friction at these points.


At 05:28 PM 1/7/2008, you wrote:

>    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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