The SAL series RF admittance point level sensor features automatic build-up immunity which is especially helpful with target materials that are sticky or may pack between the vessel wall and the probe. The guard section is used to provide this immunity and is activated with the same RF signal as the active probe section. Since current cannot flow between the same potentials, the guard section effectively blocks the current flow from the active probe through the build-up to the grounding section at the vessel wall, ensuring the accuracy and application reliability of the sensor. There are two versions of the SAL, the SAL17 and SAL18. The SAL18 is the most advanced, including pushbutton calibration and independently adjustable time delay for material detection and absence.