Capacitance Level Switch

Electronet series LCS-02 are Capacitance Type Level Switches. The vessel wall & probe forms two electrodes. 
If the vessel is of non-conductive material, the probe will be double rod type. The distance between the electrodes and surface area of the electrodes remains unchanged. The variable is the depth of the material being measured which represents the dielectric constant between two electrodes. Air and vacuum have relative dielectric constant as 1 and that of liquids is greater than 1. 
The capacitance of the capacitor therefore depends on how much material lies between the probe and vessel wall i.e. whether the probe is covered with or free from material. The capacitance changes with change in level of the material & provides switching output at the desired preset level.