PSN-L Message - Subject: RE: New Seismo

Chapman To: psnlist@.............. ; dave.nelson@............... Sent: Saturday, July 30, 2011 8:39 PM Subject: Re: New Seismo dave.nelson@............... Subject: Re: New Seismo hi Chris Am really at the end of the rope here ... just total frustration... spent all day yesterday improving the period got down to 11 sec. set up a magnetic dampening system with a strip of aluminium 1.5cm wide going in between the 2 magnets. The only thing that seems to achieve is dropping my period from 11 sec down to ~ 7 sec. It doesnt appear to do any actual dampening as the unit will just go on oscillating for ages and just slowly dying down on its own see... http://www.sydneystormcity.com/screen%20dump.bmp Hi Dave, I can't see from your photo how the magnet is mounted to interact with the Aluminium blade, or what sort of magnet it is. Can you explain further, please ? What thickness is the aluminium sheet and is it soft Aluminium or hard Aluminium Alloy, please ? I use 1/16" thick copper sheet, but you can use 1 mm thick sheet. Aluminium is weakly dia-magnetic. The damper should NOT reduce the period ! This suggests that the magnet is attracted to something on the arm ? Look at the drawings of my damper system. IT WORKS JUST FINE ! See http://www.jclahr.com/science/psn/chapman/lehman/index.html ****BTW I did take your bottom pivot advice. I have a flat steel plate on the end of the boom against the ball in the vertical Are the ball bearing AND the steel plate BOTH made of HARDENED Stainless Steel, please ? I use a medical Swann-Morton scalpel blade cut to a convenient length using a Dremmel silicon carbide cutting disk. Ordinary steel will rust and Austenitic stainless is too soft --- if you can file it, it is no good ! The reason that I am querying this, is that I can set the period of my Lehman to 25 seconds DEAD EASILY ! I have run it at a period of 60 seconds ! ****maybe you can help further ? :) Does this help ? Let me know. Regards, Chris Chapman Message

Hi=20 Ted, I remember hearing about another automotive seismograph some years = ago. The=20 story went; this guy hung a small block chevy engine = block from a hing=20 on the wall, with a big spring attached to the block and a rafter = above it.=20 Suposidley it worked remarkably well for recording local=20 events.

<<<GRIN>>> Steve Hammond PSN San Jose, Aptos, = CA

-----Original Message-----
From:=20 psnlist-request@.............. [mailto:psnlist-request@............... = On=20 Behalf Of Ted Channel
Sent: Saturday, July 30, 2011 9:18 = PM
To: psnlist@..............
Subject: Re: New=20 Seismo

Hello Folks at PSN,   A = good thing=20 about the group, is that you can ask about most any issue, and get=20 help.... Damping a large mass, which does not come up too often, = is one=20 problem I had recently.    Dave, it sounds like you are = getting=20 good advise.    I was using a 15 pound mass, and = had the=20 same problem. I used, the magnet sandwich like Chris suggested, = I just=20 needed to make the damper more powerful then usually........Dave if = you have=20 the damper plate and damper magnets in your hand.... can you feel the = eddy as=20 you move the plate? If you mass is large this eddy must feel = very=20 powerful to work......That is my two cents worth.    By = the way=20 this is the first and the last big mass for me....I saw no benefit, = but this=20 was a special project.

I have great fun designing different=20 sensors.   Not highly sophisticated, as some of the members, = but=20 simple things I can handle.   "The Big Lebowski" is my=20 latest.   Made from a car leaf spring and a bowling = ball.........as=20 a result, I also needed a powerful damper....  , I made this = vertical for Boise State University. It is a simple one second=20 vertical.........works just fine.

I have no way to post pictures, = but if you=20 are interested, and you email me I can send a picture and or a word = doc. with=20 several pictures and description.

Cheers, = Ted     =20 Tchannel@............

----- Original Message -----
From:=20 Christopher=20 Chapman

To: psnlist@.............. ; = dave.nelson@...............=20

Sent: Saturday, July 30, 2011 = 8:39=20 PM

Subject: Re: New Seismo

dave.nelson@...............
Subject:=20 Re: New Seismo

hi Chris        Am really = at the=20 end of the rope here ... just total frustration... spent all = day=20 yesterday improving the period got down to 11 sec. set up a = magnetic=20 dampening system with a strip of aluminium 1.5cm wide = going=20 in between the 2 magnets. The only thing that seems to = achieve is=20 dropping my period from 11 sec down to ~ 7 sec. It doesnt = appear=20 to do any actual dampening as the unit will just go on =

oscillating for ages and just slowly dying down on its = own =20 see... http://www.sydneystormcity.com/screen%20dump.bmp <= BR> Hi=20 Dave,

    I can't see from your photo how the = magnet is=20 mounted to interact with the Aluminium

blade, or what sort of magnet it is. Can you explain = further,=20 please ? What thickness is

the aluminium sheet and is it soft Aluminium or hard = Aluminium=20 Alloy, please ? I use 1/16"

thick copper sheet, but you can use 1 mm thick sheet. = Aluminium is=20 weakly dia-magnetic.

The damper should NOT reduce the period ! This suggests = that the=20 magnet is attracted to

something on the arm ?

    Look at the drawings of my damper = system. IT=20 WORKS JUST FINE !

    See http= ://www.jclahr.com/science/psn/chapman/lehman/index.html
****BTW =20 I did take your bottom pivot advice. I have a flat steel plate on = the end of=20 the boom against the ball in the vertical    =20 Are the ball bearing AND the steel plate BOTH made of HARDENED = Stainless=20 Steel, please ? I=20 use a medical Swann-Morton scalpel blade cut to a convenient = length=20 using a Dremmel silicon carbide=20 cutting disk. Ordinary steel will rust and Austenitic stainless is = too soft=20 --- if you=20 can file it, it is no good !   =20 The reason that I am querying this, is that I can set the period of = my=20 Lehman to 25 seconds DEAD=20 EASILY ! I have run it at a period of 60 seconds=20 ! ****maybe=20 you can help further ?   :)    =20 Does this help ? Let me know.    =20 Regards,    =20 Chris = Chapman

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