The interface circuit relies
on a simple relaxation oscillator and a microcontroller. A cable with active shielding interconnects the sensor to the interface circuit. The stability
of the active-shielding circuit is analysed by taking into account the parasitic components of both the interconnecting cable and the sensor. The
system has been experimentally tested by measuring the level of tap water in a grounded metallic container. Over a level range of 70 cm, the system
has a non-linearity error smaller than 0.35mm and a resolution better than 0.10mm for a measuring time of 20 ms.
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