Hi Chris,=20
Q   By V HAIRPINS, do you mean a piece of wire which forms a single "V" =
shape?  One for each wire, with no twist or turns?

Q  Just curious, about the magnet layout.  Why are they arranged N,S on =
the top and S,N on the bottom?
If one used a horseshoe magnet it would be Just N,S

Pictures tomorrow, I think.   Thanks, Ted
  ----- Original Message -----=20
  From: ChrisAtUpw@..........
  To: psn-l@.................
  Sent: Wednesday, October 11, 2006 12:52 PM
  Subject: Re: Building a lehman seismometer


  In a message dated 2006/10/11, tchannel@.............. writes:


    Hi Chris,    The sensor is coming along nicely. =20
    Q.   The coil is done, is it a good idea to coat the coil with glue =
or something like that just to keep the wires from getting damaged, or =
is it best just to leave it?


  Hi Ted,

         While it should be possible to varnish the coil, I have had =
nothing but trouble with this due to turns shorting out. I suggest that =
you leave it plain, but maybe wrap a length of 'self amalgamating' =
rubber tape around the outside. This rubber just sticks to itself, =
nothing else. Alternatively use paper or a cloth tape and a water based =
glue (no aromatic solvents). PVC tape tends to 'go sticky' and peel off =
after a few months. You may also be able to get large diameter heat =
shrink tube, but it tends to be expensive.  =20


    Q.  As the wires leave the coil and travel down the shaft to the =
lower pivot, what is the best way to make the transition off the shaft =
to the base?  I have seen coiled wires to form a spring, to reduce drag =
on the movement of the shaft.  I have seen large loops and small coils.  =
I don't know if they should be hanging down or left and right. You must =
have tried several different methods?


         I mount a couple of solder pins on the coil former and then use =
thin shielded microphone cable from the coil to the hinge (and from the =
upright to the amplifier). Tie / tape it to the arm every 6" or so. =
Preferably look for the cable variety that has a black conducting =
plastic shield inside the braided copper screen. This gives the best =
performance / lowest noise - otherwise just use thin microphone cable.=20

         I use two bits of pinboard, each with 2 pins, one glued to the =
arm and one to the vertical. I use a V WIRE HAIRPINS about 2" long =
standing ~vertically of 36 / 38 gauge wire. I have not tried any thicker =
wire.=20
         You can use short coils, but you have to ensure that there are =
no turns touching.
         I use a polyurethane insulated magnet wire like Beldsol. I wrap =
a turn around the pin and then solder with a hot iron - or just solder =
the end 1/8" of wire, whichever is easier. The polyurethane insulation =
melts. It is easy to replace the wires.
         The apparatus / frame should be earthed.=20

         Regards,








Hi Chris, 
Q   By V HAIRPINS, do you =
mean a piece of=20
wire which forms a single "V" shape?  One for each wire, with no =
twist or=20
turns?
 
Q  Just curious, about the magnet=20
layout.  Why are they arranged N,S on the top and S,N on the=20
bottom?
If one used a horseshoe magnet it would =
be Just=20
N,S
 
Pictures tomorrow, I think.   =
Thanks,=20
Ted

  
----- Original Message ----- 
  From:=20
  ChrisAtUpw@....... 
  
To: psn-l@.............. 
  
Sent: Wednesday, October 11, =
2006 12:52=20
  PM
  
Subject: Re: Building a lehman=20
  seismometer
  

In a=20
  message dated 2006/10/11, tchannel@..............=20
  writes:


  Hi Chris,    The sensor is coming along=20
    nicely.  
Q.   The coil is done, is it a good idea =
to coat=20
    the coil with glue or something like that just to keep the wires =
from=20
    getting damaged, or is it best just to leave it?

Hi=20
  Ted,

       While it should be =
possible=20
  to varnish the coil, I have had nothing but trouble with this due to =
turns=20
  shorting out. I suggest that you leave it plain, but maybe wrap a =
length of=20
  'self amalgamating' rubber tape around the outside. This rubber just =
sticks to=20
  itself, nothing else. Alternatively use paper or a cloth tape and a =
water=20
  based glue (no aromatic solvents). PVC tape tends to 'go sticky' and =
peel off=20
  after a few months. You may also be able to get large diameter heat =
shrink=20
  tube, but it tends to be expensive.   


  Q.  As the wires leave the coil and travel down the =
shaft=20
    to the lower pivot, what is the best way to make the transition off =
the=20
    shaft to the base?  I have seen coiled wires to form a spring, =
to=20
    reduce drag on the movement of the shaft.  I have seen large =
loops and=20
    small coils.  I don't know if they should be hanging down or =
left and=20
    right. You must have tried several different methods?

       I mount a =
couple of=20
  solder pins on the coil former and then use thin shielded microphone =
cable=20
  from the coil to the hinge (and from the upright to the amplifier). =
Tie / tape=20
  it to the arm every 6" or so. Preferably look for the cable variety =
that has a=20
  black conducting plastic shield inside the braided copper screen. This =
gives=20
  the best performance / lowest noise - otherwise just use thin =
microphone=20
  cable. 

       I use two bits of=20
  pinboard, each with 2 pins, one glued to the arm and one to the =
vertical. I=20
  use a V WIRE HAIRPINS about 2" long standing ~vertically of 36 / 38 =
gauge=20
  wire. I have not tried any thicker wire.=20
  
       You can use short coils, but =
you have=20
  to ensure that there are no turns=20
  touching.
       I use a polyurethane =

  insulated magnet wire like Beldsol. I wrap a turn around the pin and =
then=20
  solder with a hot iron - or just solder the end 1/8" of wire, =
whichever is=20
  easier. The polyurethane insulation melts. It is easy to replace the=20
  wires.
       The apparatus / frame =
should be=20
  earthed. 

      =20
  Regards,

       Chris =
Chapman=20