From: Randall Pratt rpratt@.............
Subject: RE: Seismograph Photo



Hi Chris,
=20
****I am using strips of steel from a steel measuring tape for the pivot.  =
I cut strips about 1/8=E2=80=9D wide across the tape and I use 2 pieces spa=
ced about an inch to give side to side stiffness in boom motion.  A regular=
 scissor will cut the tape and may also work to trim a double edge blade.  =
You are correct the boom is a bit high in the picture.  Before mounting the=
 boom it can be hung from a thread in the pivot clamp and the line of the t=
hread will point to the cg.=20
=20
    Thanks!
=20
****I think in most AS-1 types the cg is actually below the boom and the bo=
om should be up and not level. =20
=20
    The AS-1 should have it's boom level, as set by the spirit level. This =
also sets the position of the U magnet relative to the sensor coil.=20
    See http://www.jclahr.com/science/psn/as1/as1_dim.jpg=20

    There is a bolt mounted vertically on top of the arm close to the magne=
t, usually with two nuts and some load washers on it. You remove the arm an=
d suspend it near vertical using PVC tape over the knife edge. You then adj=
ust the positions of the nuts and washers on the bolt to set the arm vertic=
al. I don't think that this is mentioned in the manual by Tammy and Anne, s=
ince the AS-1 should be set up correctly as sold. Having said this, my AS-1=
 had a huge stack of washers and I had to fit some in between the magnet an=
d the arm and also lower the coil an equivalent amount.=20
 =20
****With my adjustable spring mounts I played with angles down to 30 degree=
s while I had the optical sensor.  Without temperature control it is to muc=
h of a struggle to maintain stability at lower angles and longer periods.  =
 The spring I have is negative length -0.191 inch.  I measured 6 weights be=
tween 7000 and 14500 grains and used linear regression on the measurements.=
  An easy way to do this is to hang a small plastic or paper cup from the s=
pring and add lead bullets to the cup. After assembly, period measurement c=
an then confirm the total boom mass since it is harder to weigh beyond the =
scale capacity. =20
=20
    I have LCD digital kitchen scales working up to 2 kgm in 2 gm intervals=
.. I also have a 200 gm scale working at 0.1 gm intervals. For anything heav=
ier, I take it to the local Post Office and use their digital parcel scales=
! This is one of the few advantages of the metric system - the small size o=
f basic unit - 28.35 gm =3D 1 oz !
 =20
****There is a hidden advantage to brazing the frame. When the garage is 10=
 degrees F the torch is warmer than a drill press!!!
=20
    Umm? I tend to think laterally - I move from the garage to the kitchen =
- which IS heated!

    Regards,

    Chris
=20










=
From: Randall Pratt rpratt@.........
o.net

Subject: RE: Seismograph Photo











Hi Chris,


 


****I am using strips of steel from a steel mea=
suring tape for the pivot.  I cut strips about 1/8=E2=80=9D wide acros=
s the tape and I use 2 pieces spaced about an inch to give side to side sti=
ffness in boom motion.  A regular scissor will cut the tape and may al=
so work to trim a double edge blade.  You are correct the boom is a bi=
t high in the picture.  Before mounting the boom it can be hung from a=
 thread in the pivot clamp and the line of the thread will point to the cg.=
 


 


    Thanks!


 


****I think in most AS-1 types the cg is actual=
ly below the boom and the boom should be up and not level.  


 


    The AS-1 should have it's bo=
om level, as set by the spirit level. This also sets the position of the U =
magnet relative to the sensor coil. 


    See http://www.jclahr.com/science/psn/as1=
/as1_dim.jpg 


 


    There is a bolt mounted vert=
ically on top of the arm close to the magnet, usually with two nuts and som=
e load washers on it. You remove the arm and suspend it near vertical using=
 PVC tape over the knife edge. You then adjust the positions of t=
he nuts and washers on the bolt to set the arm vertical. I don't think=
 that this is mentioned in the manual by Tammy and Anne, since the AS-1&nbs=
p;should be set up correctly as sold. Having said this, my AS-1 h=
ad a huge stack of washers and I had to fit some in between the magnet and =
the arm and also lower the coil an equivalent amount. 


  


****With my adjustable spring mounts I played w=
ith angles down to 30 degrees while I had the optical sensor.  Without=
 temperature control it is to much of a struggle to maintain stability at l=
ower angles and longer periods.   The spring I have is negative l=
ength -0.191 inch.  I measured 6 weights between 7000 and 14500 grains=
 and used linear regression on the measurements.  An easy way to do th=
is is to hang a small plastic or paper cup from the spring and add lead bul=
lets to the cup. After assembly, period measurement can then confirm t=
he total boom mass since it is harder to weigh beyond the scale capacity.&n=
bsp; 


 


    I have LCD digital kitchen s=
cales working up to 2 kgm in 2 gm intervals. I also have a 200 gm scale wor=
king at 0.1 gm intervals. For anything heavier, I take it to the local Post=
 Office and use their digital parcel scales! This is one of the few ad=
vantages of the metric system - the small size of basic unit - 28.35 gm&nbs=
p;=3D 1 oz !


  


****There is a hidden advantage to brazing the =
frame. When the garage is 10 degrees F the torch is warmer than a drill pre=
ss!!!


 


    Umm? I tend to think lateral=
ly - I move from the garage to the kitchen - which IS heated!=



 


    Regards,


 


    Chris