ChrisAtUpw@....... wrote:
>  
> In a message dated 22/01/2007, gpayton880@....... writes:
> 
> 
> Chris, where may I find more information on the capacitive  detectors, 

    This device which was recently discussed here uses a capacitive 
detector:

http://psn.quake.net/volksmeter/State-of-the-art_Digital_Seismograph.pdf

    This page has info on the IC connected to the capacitive sensor:

http://www.analog.com/en/prod/0%2C2877%2CAD7745%2C00.html


> please.  And, what is  "LVDT?"

    It's a linear variable differential transformer, three coils wound 
around a form with a magnetic core that moves within them. With proper 
circuitry it gives a voltage proportional to the position of the core.
    This page describes an LVDT:

http://www.keckec.com/seismo/

    I've also seen an LVDT designed and used in the LIGO project that 
uses only the three coils, with the center coil mounted on the moving 
member to replace the moving magnetic core. One advantage of this is 
there is no (or much less) "pull" on the moving part by magnetic 
induction from the excitation coil.
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