PSN-L Email List Message

Subject: Re: New Seismo
From: Christopher Chapman chrisatupw@.......
Date: Sun, 24 Jul 2011 12:28:38 -0400 (EDT)




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

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