PSN-L Email List Message

Subject: Re: New Lehman seismometer pivots
From: "Robert O. Green" rog@..........
Date: Sat, 02 May 2009 06:17:07 -0700


Is there are reason to have the coil on the boom?  Wouldn't these issues 
be eliminated if the coil was on the base plate and the magnet was on 
the boom?


Dave Nelson wrote:
> Jon,
>           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.
> cheers
> Dave Nelson
> Sydney
> Australia
> At 01:58 PM 5/1/2009 +0000, you wrote:
>> Hi
>> 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.
>> Regards.
>> Jón Frímann.
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