Hi Randy,  As a great tool, have you seen Bob's "springcalc.exe"?   Ted
  ----- Original Message -----=20
  From: ChrisAtUpw@..........
  To: psn-l@.................
  Sent: Thursday, December 21, 2006 3:13 AM
  Subject: Re: Zero length spring discusion


  In a message dated 2006/12/21, rpratt@............. writes:


    Continuing the spring discussion, what are the practical =
implications of a non-zero length?  Suppose one wants a 1.5 - 2.0 second =
vertical similar to an AS-1. It isn't difficult to get there with a =
variety of springs. =20


  Hi Randy,

         I suggest that you look up the LaCoste papers at =
http://psn.quake.net/bibliography.html=20
         As you say it is not too difficult to get about a 1 sec period, =
maybe a bit longer. However if you want to get longer periods, you do =
need the right geometry / spring load vs extension relationship. You =
won't get much above 5 secs period with a steel spring anyway. The large =
temperature coefficient of the steel eventually makes the compensation =
point highly unstable. You are trying to balance a gravitational load =
with a spring force. Professional equipment used Ni-SpanC springs which =
have a ~zero temperature coefficient.=20

         Also go to http://quake.eas.gatech.edu/Instruments/LPVERT0.htm

  If the chosen spring has zero force at say mid length how will that =
influence the=20

    operation over a zero length spring? Isn't it period that matters =
and the zero length is important only for getting the longest possible =
length in period?


         A zero length spring has a plot of physical length versus load =
which goes through zero. It is very tightly wound and it takes an =
appreciable force to extend it at all. You ''don't count'' any load =
which simply does not extend the tension spring.
         If your spring has a zero force at some mid length, you just =
won't be able to satisfy the balance conditions - even approximately - =
and you won't be able to use it to give long periods. The maths is not =
very complicated, BUT IT IS IMMUTABLE! It sets out the conditions =
required to get A STABLE BALANCE POINT.

         Regards,








Hi Randy,  As a great tool, have =
you seen=20
Bob's "springcalc.exe"?   Ted

  
----- Original Message ----- 
  From:=20
  ChrisAtUpw@....... 
  
To: psn-l@.............. 
  
Sent: Thursday, December 21, =
2006 3:13=20
  AM
  
Subject: Re: Zero length spring =

  discusion
  

In a=20
  message dated 2006/12/21, rpratt@............. =
writes:


  Continuing the spring discussion, what are the practical =

    implications of a non-zero length?  Suppose one wants a 1.5 - =
2.0=20
    second vertical similar to an AS-1. It isn't difficult to get there =
with a=20
    variety of springs.  

Hi=20
  Randy,

       I suggest that you =
look up=20
  the LaCoste papers at http://psn.quake.net/bibliography.html=20
  
       As you say it is not too =
difficult to=20
  get about a 1 sec period, maybe a bit longer. However if you want to =
get=20
  longer periods, you do need the right geometry / spring load vs =
extension=20
  relationship. You won't get much above 5 secs period with a steel =
spring=20
  anyway. The large temperature coefficient of the steel eventually =
makes the=20
  compensation point highly unstable. You are trying to balance a =
gravitational=20
  load with a spring force. Professional equipment used Ni-SpanC springs =
which=20
  have a ~zero temperature coefficient.=20
  

       Also go to=20
  http://quake.eas.gatech.edu/Instruments/LPVERT0.htm

If the =
chosen=20
  spring has zero force at say mid length how will that influence the=20
  

  operation over a zero length spring? Isn't it period =
that=20
    matters and the zero length is important only for getting the =
longest=20
    possible length in period?

       A zero =
length spring=20
  has a plot of physical length versus load which goes through zero. It =
is very=20
  tightly wound and it takes an appreciable force to extend it at all. =
You=20
  ''don't count'' any load which simply does not extend the tension=20
  spring.
       If your spring has a =
zero=20
  force at some mid length, you just won't be able to satisfy the =
balance=20
  conditions - even approximately - and you won't be able to use it to =
give long=20
  periods. The maths is not very complicated, BUT IT IS IMMUTABLE! It =
sets out=20
  the conditions required to get A STABLE BALANCE=20
  POINT.

      =20
  Regards,

       Chris =
Chapman=20