Hi again Chuck
I left out one important piece of the circuit. Chris'
reply to you jogged my memory. Since you drive the
bridge with AC, you have to have a synchronous
rectifier after the gain stages to turn the signal
back to DC. This is done with an analog switch and an
op amp. Easy.
As Chris mentioned, the homemade liquid filled tube
may be your best bet for building the sensor yourself.
I saw one of these at Cal Tech many years ago. It was
about 2 meters long and had a horizontal tube filled
with Mercury. They sensed the level of the Mercury in
a cup at each end capacitively. With today's
capacitive sensor ICs, this should be easy to do.
Good luck!
Pete  
--- Chuck Burch  wrote:

> 
> 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?  
> 
> I'm planning on using a Wheatstone bridge detector
> circuit.  Can this be improved?
> 
> Thanks for your comments.
> 
> Chuck I. Burch
> 
>
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