PSN-L Email List Message

Subject: Re: Did I get 12 second period ?
From: ChrisAtUpw@.......
Date: Mon, 25 May 2009 18:23:27 EDT


In a message dated 25/05/2009, gmvoeth@........... writes:

The  floor is level, this is the same floor where I keep my geophone, with 
any  issues.

However, the lehman sensor appears to be this high so I can get  12 to 20
second period. I am not sure why that is.
Hi Jon,
 
    It is the angle between the local vertical and the  line joining the 
centres of rotation of the top and bottom bearings which  determines the 
period.
    _http://www.jonfr.com/myndir/v/geology/lehman/p5100003.jpg.html_ 
(http://www.jonfr.com/myndir/v/geology/lehman/p5100003.jpg.html)  shows  the 
bottom bearing. You need to loosen the nuts and unscrew them so that the  head of 
the bolt is a few mm or more further AWAY from the bottom cross bar,  
towards the mass. The tighten the nuts again. You will also have to adjust  the 
top suspension. Maybe adjust the top suspension so that the bolt head is  
further away from the mass end?

The only  problem that I am dealing with now is that once I have setup the 
correct  period. I sometimes find that the coil slides to the magnets and 
gets stuck  there. I do not know why that movment happens. 
    _http://www.jonfr.com/myndir/v/geology/lehman/p5100005.jpg.html_ 
(http://www.jonfr.com/myndir/v/geology/lehman/p5100005.jpg.html) 



You have a bolt through the centre of the coil and  another one suspending 
it from the arm. Are these bolts, nuts,  washers completely NON MAGNETIC? 
eg.Brass and not nickel plated? Can you  replace the metal bolt through the 
coil with a nylon bolt? Maybe bolt or stick  the coil to a sheet of fibreglass 
/ plastic and attach this to the arm?
    What metal is the plate supporting the  magnet?
 
    Regards,
 
    Chris Chapman





In a message dated 25/05/2009, gmvoeth@........... writes:
The floor is level, this is the same floor where I keep my geophone, with an= y issues.

However, the lehman sensor appears to be this high so I= can get 12 to 20
second period. I am not sure why that is.
Hi Jon,
 
    It is the angle between the local vertical an= d the line joining the centres of rotation of the top and bottom bearings which= determines the period.
    ht= tp://www.jonfr.com/myndir/v/geology/lehman/p5100003.jpg.html show= s the bottom bearing. You need to loosen the nuts and unscrew them so that= the head of the bolt is a few mm or more further AWAY from the bottom cross ba= r, towards the mass. The tighten the nuts again. You will also have to= adjust the top suspension. Maybe adjust the top suspension so that the bolt head= is further away from the mass end?
The only problem that I am dealing with now is that once I have setup the correct= period. I sometimes find that the coil slides to the magnets and gets st= uck there. I do not know why that movment happens.
    ht= tp://www.jonfr.com/myndir/v/geology/lehman/p5100005.jpg.html

 
    You have a bolt through the centre of the coi= l and another one suspending it from the arm. Are these bolts, nuts, washers completely NON MAGNETIC? eg.Brass and not nickel plated? Can= you replace the metal bolt through the coil with a nylon bolt? Maybe bolt or= stick the coil to a sheet of fibreglass / plastic and attach this to the arm?
    What metal is the plate supporting the magnet?
 
    Regards,
 
    Chris Chapman

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