PSN-L Email List Message

Subject: RE: Springs again
From: "Paul Cianciolo" Paulc@........
Date: Thu, 19 Jul 2007 13:46:51 -0400


Hello Chris,

Thanks again as always for the help.

I have abandoned the geometry I was using (at least for the moment) in favor
of the the" AS-1 like" geometry you suggested.
A very quick couple of experiments on the bench showed with the same
pendulum length that I had been using,  period went from 1.1 secs to a bit
over 3 secs.

This was done using springs that I had in the junk drawer, but had
overlooked since the previous model used a much shorter spring.

                                Pivot
                                   I
MASS
               ----@----@---------------------------------------------------
MASS
                           S
MASS
                                              P
                                               R
                                                I
                                               N
                                               G
  __________________________________________________________________________
__________

Chris,

In the picture above the spring provides upward restoration.
The pivot is a hard steel rod with its axis horizontal and perpendicular
with the pendulum.

The springs was a valve spring several types from different engines.

My thought was if I could get a "clock" spring to work, place it at the
pivot point and then build lateral bearings.

The assumption was that the clock spring would appear as a very long spring
since it was wound on itself.

For the time being I will stick with the AS-1 architecture.

The purpose here is to log close in events.

Thank you

PauLC






iginal Message-----
From: psn-l-request@.............. [mailto:psn-l-request@.................
Behalf Of ChrisAtUpw@.......
Sent: Tuesday, July 17, 2007 10:26 PM
To: psn-l@..............
Subject: Re: Springs again


  In a message dated 2007/07/17, Paulc@........ writes:


    My vertical sensor is the type with a lever arm that is 26" long with a
mass
    at one end.
    The other end of the lever arm has a pivot point about 2" from the end,
and
    a spring on the end to a base plate.


  Hi Paul,

         This is a bit difficult to visualise. Can you make a rough drawing
using text characters?


    This arrangement certainly not a new idea, is new to me.,
    This arrangement yields a 1.1 approx. sec period.
    By careful adjustment of the pivot point and spring location, I can vary
the
    period and the mass needed to achieve balance.


         You can get out to 4 or 5 seconds, but beyond this you need NiSpanC
springs to keep the system stable with ambient temperature variations.
However, you can extend this period either electronically or using software
up to ~x10. See the Roberts circuit for geophones in psn references and on
John Lahr's website. It may be easier to make a system for 2.5 seconds and
then extend this to 25 seconds.
         The spring attachment point needs to be maybe 1/2" to 1" above the
horizontal arm.


    2 questions.

    1) What is the relationship between spring position, pivot location, and
    mass weight.
    As I would like to try to optimize this design , if indeed this is a
valid
    path to follow.


         How good is your applied maths? This is a fairly simple triangle of
forces problem. You usually start with a coil spring and adjust the arm,
mass etc to suit.

         See the spring calculator at
http://jclahr.com/science/psn/mcclure/springcalc/index.html and also
http://jclahr.com/science/psn/mcclure/vert1/vert2.html

         Is your seismometer design anything like
http://jclahr.com/science/psn/hill/index.html ? I would strongly advise you
to use electromagnetic damping as opposed to oil.

         Have a look at http://quake.eas.gatech.edu/Instruments/LPVERT0.htm


    2) If a rule of thumb....the longer the spring, the greater the period,
    within the obvious constraints applies.
    Has or why not has a vertical sensor been tried with a watch spring,
    mainspring,  arrangement been tried.


         This is just how long period verticals are designed, but using long
triangular shaped leaf springs. Clock type coil springs have too many
vibration modes. 'Mouse trap' type torsion coil springs have been used.

          For a simple spring, the extension E = g x T^2 / (2 x Pi)^2, where
T is the period. Thus to get a period of say 10 sec, you need an extension
of ~25 metres....


    Sort of a torsion spring, but one with many turns and greater length.
    Perhaps my assumption that the main spring arrangement equates to a
longer
    spring is faulty?


         No, but this cannot be extended very far, or you start to see the
spring vibration modes.

         You can also make a very good horizontal seismometer using a U tube
water manometer.

         Regards,

         Chris Chapman





Hello=20 Chris,
 
Thanks=20 again as always for the help.
 
I have=20 abandoned the geometry I was using (at least for the moment) in favor of = the=20 the" AS-1 like" geometry you suggested.
A very=20 quick couple of experiments on the bench showed with the = same pendulum=20 length that I had been using,  period went from 1.1 secs to a bit = over 3=20 secs.
 
This=20 was done using springs that I had in the junk drawer, but had overlooked = since=20 the previous model used a much shorter spring.
          &nbs= p;            = ;        
          &nbs= p;            = ;        =20 Pivot      
          &nbs= p;          =20             &= nbsp;I         &n= bsp;           &nb= sp;           &nbs= p;            = ;            =             &= nbsp;           &n= bsp;           &nb= sp;           &nbs= p;        =20   MASS
          &nbs= p;   =20 ----@----@---------------------------------------------------MASS<= /SPAN>
     =20             &= nbsp;       =20 S         &n= bsp;           &nb= sp;           &nbs= p;            = ;          =20    =20 MASS           &nb= sp;           &nbs= p; =20
           &nbs= p;            = ;            =          =20 P
          &nbs= p;            = ;        =20             &= nbsp; =20 R
          &nbs= p;            = ;            =        =20      I
          &nbs= p;            = ;            =          =20   N
          &nbs= p;            = ;            =        =20    G
 =20 _________________________________________________________________________= ___________
       &nbs= p;            = ;            =             &= nbsp;                 &nbs= p;            = ;            =                   &nbs= p;            = ;            =             &= nbsp;           &n= bsp;           &nb= sp;           
Chris,
 
In the picture above the spring = provides upward=20 restoration.
The pivot is a hard = steel rod with=20 its axis horizontal and perpendicular with the pendulum.
 
The springs was a valve = spring=20 several types from different engines.
 
My thought was if I = could get a=20 "clock" spring to work, place it at the pivot point and then build = lateral=20 bearings.
 
The assumption was that = the clock=20 spring would appear as a very long spring since it was wound on=20 itself.
 
For the time being I = will stick with=20 the AS-1 architecture.
 
The purpose here is to = log close in=20 events.
 
Thank you
 
PauLC
 
 
 
 
 
 
iginal Message-----
From:=20 psn-l-request@.............. [mailto:psn-l-request@...............On = Behalf=20 Of ChrisAtUpw@.......
Sent: Tuesday, July 17, 2007 10:26=20 PM
To: psn-l@..............
Subject: Re: Springs=20 again

In = a message=20 dated 2007/07/17, Paulc@........ writes:

My vertical sensor is the type with a lever arm that is = 26" long=20 with a mass
at one end.
The other end of the lever arm has a = pivot=20 point about 2" from the end, and
a spring on the end to a base=20 plate.


Hi=20 Paul,

       This is a bit = difficult to=20 visualise. Can you make a rough drawing using text = characters?


This arrangement certainly not a new idea, is new to=20 me.,
This arrangement yields a 1.1 approx. sec period.
By = careful=20 adjustment of the pivot point and spring location, I can vary = the
period=20 and the mass needed to achieve balance.


       You can=20 get out to 4 or 5 seconds, but beyond this you need NiSpanC springs to = keep=20 the system stable with ambient temperature variations. However, you = can extend=20 this period either electronically or using software up to ~x10. See = the=20 Roberts circuit for geophones in psn references and on John Lahr's = website. It=20 may be easier to make a system for 2.5 seconds and then extend this to = 25=20 seconds.
       The spring attachment = point=20 needs to be maybe 1/2" to 1" above the horizontal arm.


2 questions.

1) What is the relationship between = spring=20 position, pivot location, and
mass weight.
As I would like to = try to=20 optimize this design , if indeed this is a valid
path to=20 follow.


       How=20 good is your applied maths? This is a fairly simple triangle of forces = problem. You usually start with a coil spring and adjust the arm, mass = etc to=20 suit.

       See the spring = calculator at=20 http://jclahr.com/science/psn/mcclure/springcalc/index.html and also=20 = http://jclahr.com/science/psn/mcclure/vert1/vert2.html

  = ;    =20 Is your seismometer design anything like=20 http://jclahr.com/science/psn/hill/index.html ? I would strongly = advise you to=20 use electromagnetic damping as opposed to=20 oil.

       Have a look at=20 http://quake.eas.gatech.edu/Instruments/LPVERT0.htm


2) If a rule of thumb....the longer the spring, the = greater the=20 period,
within the obvious constraints applies.
Has or why not = has a=20 vertical sensor been tried with a watch spring,
mainspring,  = arrangement been tried.


       This is=20 just how long period verticals are designed, but using long triangular = shaped=20 leaf springs. Clock type coil springs have too many vibration modes. = 'Mouse=20 trap' type torsion coil springs have been used.

        For a = simple=20 spring, the extension E =3D g x T^2 / (2 x Pi)^2, where T is the = period. Thus to=20 get a period of say 10 sec, you need an extension of ~25 = metres....

Sort of a torsion spring, but one with many turns and = greater=20 length.
Perhaps my assumption that the main spring arrangement = equates to=20 a longer
spring is=20 faulty?

       No, = but this=20 cannot be extended very far, or you start to see the spring vibration = modes.=20

       You can also make a very = good=20 horizontal seismometer using a U tube water=20 manometer.

      =20 Regards,

       Chris = Chapman
=20

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