PSN-L Email List Message

Subject: Re: New Lehman seismometer pivots
From: Dave Nelson dave.nelson@...............
Date: Sat, 02 May 2009 16:02:47 +1000

          As I told you several weeks ago and Bob McClure said within the last
couple of days .....
leave it hanging loose from the boom. Cut it near the lower pivot,
secure it to the boom, and join it with coils of fine copper wire to
terminals on the frame. The terminals should be located as near to the
lower pivot as possible."

Jon.... You MUST do this you, will NEVER achieve long period, free motion of the
arm until you get this sorted out.  It is absolutely essential to get rid of that huge
thick cable coming off the pivot end of the boom, it will be totally destroying any
attempt you make to try to get any decent sort of period from the seismometer.
Until you change that, almost anything else you do to the unit will be worthless.
see how it is done on this commercial long period seismo that I and others are/have used .....

you can see that in this case there are 2 pair of cables coming along the boom
( there are 2 pickup coils on this seismo)  they are terminated then VERY fine wire connects them to terminals on the vertical part of the frame.  Use 26 - 30 swg enamelled wire ( the finer the better).  and also use finer cable between the pickup coil and the terminal point  that that thick cable you are currently using.

Dave Nelson

At 01:58 PM 5/1/2009 +0000, you wrote:
I am still unable to get the sensor frequancy below 0.4Hz. But this
design is a lot more flexable then the last one I used.

After the weekend I am going to do one more change. I plan to change the
setting of the arm. So it has not such sharp angle, but I belive that is
hampering my effort in getting the frequancy below 0.4Hz, as sharp angle
means faster movement of the arm.

J=F3n Fr=EDmann.

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