Apparatus including a capacitive probe for measuring the level and/or the volume of a liquid

Apparatus for measuring the level of a liquid contained in a tank, the apparatus comprising a capacitive probe including at least two separate, generally vertical, parallel main plates for immersion in the liquid, means for supporting the plates in the tank, spacer means placed between the plates so as to keep the plates at a constant distance from each other, capacitance-measuring means having a detection input and a ground, the detection input being connected to a first one of the main plates and the ground being connected to a second one of the main plates, guard ring surrounding the first plate, a potential copying stage having its input connected to the first plate and its output connected to the guard ring, and a central unit connected to said capacitance-measuring means so as to determine the level of the liquid by calculating a coefficient K such that:

• K=(Cmes-Cair)/(Cimm-Cair), where:
• Cmes=the measuring capacitance between the first and second plates,
• Cair=the capacitance of the first plate and the second plate in air,
• Cimm=the capacitance of the first plate and the second plate when they are totally immersed;
• and whereby K is defined as the area of the first plate in the liquid divided by the total area of the first plate.