Short description:

Tube inside of another tube, insulated from each other, open at both 
ends - forms a capacitor

Tube assembly is mounted inside vessel for which level sensing is needed 
such that the percentage of gap filled between the two plates (inner and 
outer tubes) of the capacitor varies as the fluid level rises

As the dielectric constant of the fluid is different than the dielectric 
constant of the gas, the capacitance of the sensor will vary as the gap 
is filled.  It is not necessary that this function be linear (it never 
is), only that it be properly characterized. 

Capacitance measuring function is up to you.  Calibration and 
linearization of result, likewise.

Works well in cases where the dielectric constant of the fluid is known 
and constant and where you don't want moving parts (aircraft fuel tanks 
often use these).

Dave


alan smith wrote:

>I'm looking for a technical description of just how these sensors work.  Google has given me alot of vendors and devices, but so far havent seen anything about *how* they work, etc.
> 
>Has anyone ever used one in a project?
> 
> 
>
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