Hi,
 
  With regard to zero-length springs, it might be of interest to note  that 
the springs in an angle poise lamp are negative length. That is the  backward 
extrapolation intersects the axis on the negative side of zero  but due to 
non-linearity, moves through zero to the positive side as the  force is increased. 
It is possible to adjust the force to produce an intersect  at zero but this 
point is not stable with temperature. For a vertical  seismometer the period 
can be set to 12 to 15 seconds and may remain in  this state for a few hours in 
a domestic environment. Setting such a system  to 5 seconds instead produces 
a high period stability even though  there is a length change with 
temperature.   
 
 
Martin    



   





Hi,
 
  With regard to zero-length springs, it might be of interest to n=
ote=20
that the springs in an angle poise lamp are negative length. That is the=20
backward extrapolation intersects the axis on the negative side of zero=
=20
but due to non-linearity, moves through zero to the positive side as th=
e=20
force is increased. It is possible to adjust the force to produce an interse=
ct=20
at zero but this point is not stable with temperature. For a vertical=20
seismometer the period can be set to 12 to 15 seconds and may remain in=
=20
this state for a few hours in a domestic environment. Setting such a sy=
stem=20
to 5 seconds instead produces a high period stability even though=20
there is a length change with temperature.   
 
 
Martin