Hi Chris, =20
>So why not chop a few turns off the spring? ! Maybe make two, with half =
length springs?...........I could have, but gathering the loops aloud me =
to add and subtract to adj the length.


>Have you tried putting thermal insulation around the tube?  ..........I =
could, but the room is temperature stable, so I have not.

Thanks, Ted




  ----- Original Message -----=20
  From: ChrisAtUpw@..........
  To: psn-l@.................
  Sent: Thursday, July 26, 2007 2:42 PM
  Subject: Re: "P" ky "Slinky"


  In a message dated 2007/07/26, tchannel1@............ writes:


    With the rod+magnets+nuts there was no more room for a mass.  I =
tried addition mass and it pulled the spring too long.  I wanted to =
limit the total height to 7', but cut it down to 5'....I think at 7' the =
period was 2.4, and at 5' it was 2.2?


  Hi Ted,

         So why not chop a few turns off the spring? ! Maybe make two, =
with half length springs?


    Paul C. suggested I use two ring magnets, one entering the top of =
the coil, and the other exiting the bottom of the coil.
    I started with one magnet 1/2 (deep inside the coil), but I did not =
like the results. =20


         This would give ~zero output at the centre of the coil.
        =20
  I then moved the magnet to the top of the coil, just entering, that =
worked better.  I=20

    then added another magnet, two together, 1 and 1/2 magnets inside =
the top of the coil. This worked well. To try Paul's idea, I would just =
need to open it up and move the spacing nuts and magnets.


         You would probably need the magnets mounted in opposition, but =
this arrangement should reduce environmental magnetic forces on the =
seismometer.=20

               For the sensor you would probably do to better to make an =
analogue if a LVDT. Wind two coils end to end and connect them in =
opposition. Then place the magnet(s) in the centre. The output can be =
made nearly independent of the vertical position over the length of the =
magnet(s) / length of the coils, whichever is shorter.

         You could make an anti rotation, anti pendulum swing damper =
with two pairs of bar magnets in a cross inside a copper tube, or four =
copper plates. You could also try square Al tube, or bent sheet? You =
could probably adjust this to supply the vertical damping as well?

         You might find that about a 2 second period is optimal? This =
should bring in the P waves nicely, but reduce thermal and microseism =
disturbances. Have you tried putting thermal insulation around the tube?

         Regards,

         Chris Chapman







Hi Chris,  
>So why not chop a few turns off the =
spring? !=20
Maybe make two, with half length springs?...........I could have, but =
gathering=20
the loops aloud me to add and subtract to adj the length.
 
 

>Have you tried putting thermal insulation around the=20
tube?  ..........I could, but the room is temperature stable, =
so I=20
have not.
 
Thanks, Ted





  
----- Original Message ----- 
  From:=20
  ChrisAtUpw@....... 
  
To: psn-l@.............. 
  
Sent: Thursday, July 26, 2007 =
2:42=20
  PM
  
Subject: Re: "P" ky =
"Slinky"
  

In a=20
  message dated 2007/07/26, tchannel1@............=20
writes:


  With the rod+magnets+nuts there was no more room for a=20
    mass.  I tried addition mass and it pulled the spring too =
long.  I=20
    wanted to limit the total height to 7', but cut it down to 5'....I =
think at=20
    7' the period was 2.4, and at 5' it was 2.2?

Hi=20
  Ted,

       So why not chop a few =
turns=20
  off the spring? ! Maybe make two, with half length springs?


  Paul C. suggested I use two ring magnets, one entering =
the top=20
    of the coil, and the other exiting the bottom of the =
coil.
I started with =
one magnet 1/2=20
    (deep inside the coil), but I did not like the results.  =


       This=20
  would give ~zero output at the centre of the=20
  coil.
       
I then moved the =
magnet to=20
  the top of the coil, just entering, that worked better.  I =


  then added another magnet, two together, 1 and 1/2 =
magnets=20
    inside the top of the coil. This worked well. To try Paul's idea, I =
would=20
    just need to open it up and move the spacing nuts and=20
  magnets.

       You =
would=20
  probably need the magnets mounted in opposition, but this arrangement =
should=20
  reduce environmental magnetic forces on the seismometer.=20
  =


           =
; =20
  For the sensor you would probably do to better to make an analogue if =
a LVDT.=20
  Wind two coils end to end and connect them in opposition. Then place =
the=20
  magnet(s) in the centre. The output can be made nearly independent of =
the=20
  vertical position over the length of the magnet(s) / length of the =
coils,=20
  whichever is shorter.

       You =
could=20
  make an anti rotation, anti pendulum swing damper with two pairs of =
bar=20
  magnets in a cross inside a copper tube, or four copper plates. You =
could also=20
  try square Al tube, or bent sheet? You could probably adjust this to =
supply=20
  the vertical damping as =
well?

       You=20
  might find that about a 2 second period is optimal? This should bring =
in the P=20
  waves nicely, but reduce thermal and microseism disturbances. Have you =
tried=20
  putting thermal insulation around the=20
  tube?

      =20
  Regards,

       Chris=20
Chapman