Dave Nelson dave.nelson@...............
Subject: New Seismo

ok got around to taking a pic of the new Lehman
ttp://www.sydneystormcity.com/IMGP2023a.jpg
still waiting for the first decent quake M6+ to see its response
ill then I am guessing at the amount of dampening I need for it.
Hi Dave,
    It looks nice! What period have you set it to, please?
I suggest that you aim for 25 seconds.
I can't quite see how you have attached the mass plates to=20
the arm. Are they crimped / punched in place?=20
How does the variable damping work ? I can't see that either!=20
See http://www.jclahr.com/science/psn/chapman/lehman/index.html=20
I stick a label with a vertical line on it onto the mass and=20
view the line with a magnifying glass through a transparent=20
plastic ruler. I deflect the mass 10 mm and release it. The=20
mass moves back toward the balance point and usually past it.=20
I observe how far it moves past the balance point. I increase=20
/ decrease the damping until the mass goes 1/2 mm past the=20
balance point and then moves slowly back to zero without any=20
oscillations. The arm is then set to 0.7 critical damping.=20
The amount of damping needed decreases as the set period is=20
increased.
    I hope that this helps.
     Regards,
     Chris Chapman





=
Dave Nelson dave.nelson@optu=
snet.com.au

Subject: New Seismo



ok got=
 around to taking a pic of the new Lehman
ht=
tp://www.sydneystormcity.com/IMGP2023a.jpg

still waiting for the first decent quake M6+ to see its response
Till then I am guessing at the amount of dampening I need for it.

Hi Dave,
=
    It looks nice! What period have you set it to, please?
I suggest =
that you aim for 25 seconds.
I can't quite see how you have attached the mass plates=
 to 
the =
arm. Are they crimped / punched in place? 
How does the variable damping work ? I ca=
n't see that either! 
See http://www.jclahr.com/science/psn/chapman/lehman/index.html 
I sti=
ck a label with a vertical line on it onto the mass and 
<=
PRE style=3D"FONT-SIZE: 9pt">view the line with a magnif=
ying glass through a transparent 

plastic ruler. I deflect the mass 10 mm and releas=
e it. The 

mass moves back toward the balance point and usually past it. 

I observe how far i=
t moves past the balance point. I increase 

/ decrease the damping until the mass go=
es 1/2 mm past the 

balance point and then m=
oves slowly back to zero without any 

oscillations. The arm is then set to =
0.7 critical damping. 

<=
FONT size=3D3>The amount of damping needed decreases as the set period is <=
/FONT>

increased=
..

    I h=
ope that this helps.

     Regards,

     Chris Chapman