From: "tchannel" tchannel@..............

Date: Thu, 21 Dec 2006 08:29:06 -0700

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@.......Sent:Thursday, December 21, = 2006 3:13=20 AMSubject:Re: Zero length spring = discusionIn 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