In a message dated 2007/09/14, ciburch@........... writes:

> I am drafting plans to build a three electrode spirit level style tiltmeter 
> to use as a 
> horizontal seismometer.  Any hints on construction?  What liquid is best?  
> Are 
> surface tension and / or viscosity critical?  

Hi Chuck,

       Send an EMail to Dave Nelson davefnelson@....... and join the FMES 
group? The technology / techniques for liquid horizontal seismometers have been 
developed and construction details and circuit diagrams are available. These 
systems have been extended out to 350 seconds.
       They are basically a horizontal sense tube with dashpot height sensors 
at the ends. They have two outputs. A tilt signal is available directly and 
also a capacity coupled horizontal seismic velocity signal. They are 
constructed out of PVC pipe and use a water + additive sense fluid. They use AC 
excitation and phase sensitive detection.
       The viscosity is not critical, but you severely damp the tilt response 
to get a broad band signal. You add a surfactant to reduce the surface 
tension. The system is about 10" long and is mounted with the electronics inside a 
square Al tube to control thermal gradients and to provide electrostatic 
screening.
       They can be constructed DIY quite easily. 

> I'm planning on using a Wheatstone bridge detector circuit. Can this be 
> improved?
> 
       Very considerably! 

       Regards,

       Chris Chapman   
In a me=
ssage dated 2007/09/14, ciburch@........... writes:



I am drafting plans to build a=20=
three electrode spirit level style tiltmeter to use as a 

horizontal seismometer.  Any hints on construction?  What liquid i=
s best?  Are 

surface tension and / or viscosity critical?  




Hi Chuck,



       Send an EMail to Dave Nelson davefnelson@....... and join the FMES gr=
oup? The technology / techniques for liquid horizontal seismometers have bee=
n developed and construction details and circuit diagrams are available. The=
se systems have been extended out to 350 seconds.

       They are basically a horizontal sense t=
ube with dashpot height sensors at the ends. They have two outputs. A tilt s=
ignal is available directly and also a capacity coupled horizontal seismic v=
elocity signal. They are constructed out of PVC pipe and use a water + addit=
ive sense fluid. They use AC excitation and phase sensitive detection.

       The viscosity is not critical, but you=20=
severely damp the tilt response to get a broad band signal. You add a surfac=
tant to reduce the surface tension. The system is about 10" long and is moun=
ted with the electronics inside a square Al tube to control thermal gradient=
s and to provide electrostatic screening.

       They can be constructed DIY quite easil=
y. 



I'm planning on using a Wheatst=
one bridge detector circuit. Can this be improved?



       Very considerably! 



       Regards,



       Chris Chapman