## PSN-L Email List Message

From: ChrisAtUpw@.......
Date: Tue, 31 Jul 2007 20:47:17 EDT

```In a message dated 2007/08/01, gpayton880@....... writes:

> Will someone please explain what a "zero length spring" is?

Hi Jerry,

A zero length spring is a TIGHTLY WOUND extension type spring, often
with pull loops on each end. If you add increasing weight to it, it does not
extend at all until some critical weight is reached. Increasing the weight
further increases the length proportional to the weight. You measure between the
loops on the ends, or between two clamp points if it just has straight end
wires.
There is thus a 'step' in the characteristic. However, if you plot the
applied weight against the overall length and then extend the line below the
step back towards zero, the line goes through the zero load / zero length
point.
This is the length that the spring would have if the coils did not
prevent it from contracting. It is used on older type vertical seismometers to
obtain a long natural period.  See LaCoste references on psn and photos at
http://www.geocities.com/meredithlamb/page026.html

Regards,

Chris Chapman
In a message dated 2007/08/01, gpay=
ton880@....... writes:

ain what a "zero length spring" is?

Hi Jerry,

A zero length spring is a TIGHTLY WOUND=
extension type spring, often with pull loops on each end. If you add increa=
sing weight to it, it does not extend at all until some critical weight is r=
eached. Increasing the weight further increases the length proportional to t=
he weight. You measure between the loops on the ends, or between two clamp p=
oints if it just has straight end wires.
There is thus a 'step' in the character=
istic. However, if you plot the applied weight against the overall length an=
d then extend the line below the step back towards zero, the line goes throu=
gh the zero load / zero length point.
This is the length that the spring woul=
d have if the coils did not prevent it from contracting. It is used on older=
type vertical seismometers to obtain a long natural period.  See LaCos=
te references on psn and photos at http://www.geocities.com/meredithlamb/pag=
e026.html

Regards,

Chris Chapman
```