The radio frequency admittance switch measures and controls material levels by detecting changes in the electrical reactance (capacitive reactance and impedance) between the probe and the storage tank. It is an internal electronic unit, consisting of a probe that measures the reactance between the probe's measuring pole and the unloaded tank, forming a balanced bridge circuit and generating a stable oscillating signal. When the measured medium covers the probe's measuring pole, it causes a change in the electrical reactance between the probe and the tank, leading to an unbalanced bridge circuit and the cessation of oscillating signals. Subsequently, the downstream circuit detects this change and outputs an alarm signal.