In order to eliminate false alarm given due to medium with high viscosity sticking onto the probe , a special material acting as an insulation electrode have been added in between the active section and the grounding section.
As shown in the diagram, sensing probe always experience medium clogging on it and thereby produces a capacitance and resistance between the 3 parts. Since the electric field between the active section and the guard section is round shaped, there will be no current passing through the medium between the electrodes.

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