Jon,

          As I told you
several weeks ago and Bob McClure said within the last 

couple of days .....

"DO SOMETHING ABOUT THE WIRE LEAD TO THE COIL!!! You cannot
just 

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 ..... 
www.sydneystormcity.com/990605-013a.jpg


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.

J=F3n Fr=EDmann.