Hi Dave,
Looks good.
I notice from your picture the top pivot is a long way out from the bottom,
I feel that would give a short period.
The ball fitted to the mast with a polished lathe bit on the boom provides a
better pivot, not inclined to slip as easy.
Just a few thoughts
Regards
Dale
From: psnlist-request@.............. [mailto:psnlist-request@...............
On Behalf Of Dave Nelson
Sent: Monday, 25 July 2011 8:16 AM
To: psnlist@..............
Subject: Re: New Seismo
Thanks for your thoughts guys
hmmmm am a bit worried that there is something fundamentally wrong with
it. There was a M6.2 off Japan
overnite only 8000km away and nothing recorded. I would have
expected that even with underdampening that that event would
have showen up There is a screen dump gif image on my wwww
site http://www.sydneystormcity.com/untitled.gif
you will see that there is a pretty much steady low freq signal there,
varying in intensity, in winquake it has a
~ 3.5 sec period. The additional noise towards the end of
the display is the morning traffic becoming active with its
hi freq component.
Hey Pete R. yes thats the coil you sent me :) it is putting
out plenty of signal.
Steve H. the frame was propane gas aluminium welded. The
frame is made of 10mm thick, 50mm wide aluminium bar.
The boom is 16mm diam aluminium bar. The 2 lead weights are
2 pound diving belt weights, holes bored in them and then
slidden (<<-- horrible word haha) onto the end of the boom.
The pickup coil sits between 2 rare earth disc magnets
~ 1.5 cm diameter.
The dampening at the moment is just a cylindrical rare earth
magnet below the lower plate of the plates that support the
pickup magnets.
I am not totally happy with the lower pivot. I was going to have ball
bearings butted against each other. But they wont
sit together. Even just the signle ball bearing in the end
of the boom wont sit happily against the vertical bar.
There is just so much upwards force at that end of the boom caused by the
downwards force of the weight at the other end.
cheers
Dave
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 can't see that either!
See http://www.jclahr.com/science/psn/chapman/lehman/index.html
I stick a label with a vertical line on it onto the mass and view the line
with a magnifying glass through a transparent plastic ruler. I deflect the
mass 10 mm and release it. The mass moves back toward the balance point and
usually past it.
I observe how far it moves past the balance point. I increase / decrease the
damping until the mass goes 1/2 mm past the balance point and then moves
slowly back to zero without any oscillations. The arm is then set to 0.7
critical damping.
The amount of damping needed decreases as the set period is
increased.
I hope that this helps.
Regards,
Chris Chapman
Hi Dave,
Looks good.
I notice from your picture the top pivot is a long way =
out from
the bottom, I feel that would give a short =
period.
The ball fitted to the mast with a polished lathe bit on =
the
boom provides a better pivot, not inclined to slip as =
easy.
Just a few thoughts
Regards
Dale
From:=
psnlist-request@.............. [mailto:psnlist-request@............... =
On
Behalf Of Dave Nelson
Sent: Monday, 25 July 2011 8:16 AM
To: psnlist@..............
Subject: Re: New Seismo
Thanks for your thoughts guys
hmmmm am a bit worried that there is something =
fundamentally
wrong with it. There was a M6.2 off Japan
overnite only 8000km away and nothing recorded. I would =
have
expected that even with underdampening that that event would =
have showen up There is a screen dump gif image on my =
wwww
site http://www.sydneysto=
rmcity.com/untitled.gif
you will see that there is a pretty much steady low freq signal =
there,
varying in intensity, in winquake it has a
~ 3.5 sec period. The additional noise towards the end of =
the display is the morning traffic becoming active with its =
hi freq component.
Hey Pete R. yes thats the coil you sent me :) it =
is
putting
out plenty of signal.
Steve H. the frame was propane gas aluminium welded. =
The
frame is made of 10mm thick, 50mm wide aluminium bar.
The boom is 16mm diam aluminium bar. The 2 lead weights are =
2 pound diving belt weights, holes bored in them and then
slidden (<<-- horrible word haha) onto the end of the =
boom.
The pickup coil sits between 2 rare earth disc magnets
~ 1.5 cm diameter.
The dampening at the moment is just a cylindrical rare earth =
magnet below the lower plate of the plates that support the =
pickup magnets.
I am not totally happy with the lower pivot. I was going to =
have ball
bearings butted against each other. But they wont
sit together. Even just the signle ball bearing in the end =
of the boom wont sit happily against the vertical bar.
There is just so much upwards force at that end of the boom caused =
by the
downwards force of the weight at the other end.
cheers
Dave
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 can't see that either!
See http=
://www.jclahr.com/science/psn/chapman/lehman/index.html
I stick a label with a vertical =
line on it
onto the mass and view the line with a magnifying glass through a =
transparent
plastic ruler. I deflect the mass 10 mm and release it. The mass moves =
back
toward the balance point and usually past it.
I observe how far it moves =
past the
balance point. I increase / decrease the damping until the mass goes 1/2 =
mm
past the balance point and then moves slowly back to zero without any
oscillations. The arm is then set to 0.7 critical damping. =
The amount of damping needed
decreases as the set period is
increased.
I hope =
that this
helps.
=
Regards,
=
Chris
Chapman
![http://www.sydneysto= rmcity.com/untitled.gif](3D"http://www.sydneystormcity.com/untitled.gif"){kind=link}