In a message dated 2006/10/01, gmvoeth@........... writes:

> Hello Chris;
> http://jclahr.com/science/psn/chapman/lehman/index.html
> Yes, I like that design very much.
> 
> Do you make a vertical version of that
> with a spring where the wire is ?

Hi Geoff,

       Not at the moment. 

       Long period verticals are much more difficult to make than long period 
horizontals. The essential properties to give a 'zero length extension 
spring' were worked out by LaCoste in the mid 1930's. See 
http://psn.quake.net/bibliography.html To balance the vertical force of gravity on the mass requires a 
very constant force. You need a Ni-SpanC spring and a lot of careful design to 
enable you to get stable periods over about 10 secs. The elastic properties of 
steel springs are much too temperature sensitive.

       One alternative is to use a steel leaf spring, but to provide 
electronic force feedback to both compensate for incoming signals and to remove the 
drift. The feedback essentially tries to hold the mass stationary. See great 
example at http://www.bryantlabs.net/seismo.html
 
       Another alternative is to use a steel spring to produce a vertical 
with a period of 1 to 3 seconds, which is not too difficult to do and then extend 
the response electronically by x10 to x20 - as you can for a geophone 
(Roberts' circuit). You could probably extend the period of your 1 Hz geophone to 
about ~20 sec this way, but you would likely see some increase in sensor noise. 

       This period extension method is attempted on the AS-1. See 
http://jclahr.com/science/psn/as1/index.html The basic period is about 1.5 sec and a 
response from 3Hz to 20 sec is claimed, but the manufactured item costs about US 
$600.

       Regards,

       Chris Chapman
In a me=
ssage dated 2006/10/01, gmvoeth@........... writes:



Hello Chris;

http://jclahr.com/science/psn/chapman/lehman/index.html

Yes, I like that design very much.



Do you make a vertical version of that

with a spring where the wire is ?




Hi Geoff,



       Not at the moment. 



       Long period verticals are much more dif=
ficult to make than long period horizontals. The essential properties to giv=
e a 'zero length extension spring' were worked out by LaCoste in the mid 193=
0's. See http://psn.quake.net/bibliography.html To balance the vertical forc=
e of gravity on the mass requires a very constant force. You need a Ni-SpanC=
 spring and a lot of careful design to enable you to get stable periods over=
 about 10 secs. The elastic properties of steel springs are much too tempera=
ture sensitive.



       One alternative is to use a steel leaf=20=
spring, but to provide electronic force feedback to both compensate for inco=
ming signals and to remove the drift. The feedback essentially tries to hold=
 the mass stationary. See great example at http://www.bryantlabs.net/seismo.=
html

 

       Another alternative is to use a steel s=
pring to produce a vertical with a period of 1 to 3 seconds, which is not to=
o difficult to do and then extend the response electronically by x10 to x20=20=
- as you can for a geophone (Roberts' circuit). You could probably extend th=
e period of your 1 Hz geophone to about ~20 sec this way, but you would like=
ly see some increase in sensor noise. 



       This period extension method is attempt=
ed on the AS-1. See http://jclahr.com/science/psn/as1/index.html The basic p=
eriod is about 1.5 sec and a response from 3Hz to 20 sec is claimed, but the=
 manufactured item costs about US $600.



       Regards,



       Chris Chapman