The difference between RF admittance level switch and capacitive level switch:
Radio frequency admittance level switch and capacitive level switch are two common types of level switches. Visually, the RF admittance probe consists of three layers of metal isolated from each other: the measuring electrode, the protective electrode, and the tank electrode, while the capacitive probe consists of two layers of metal isolated from each other: the measuring electrode and the tank electrode. The difference in the structure of the above probes is due to the addition of an anti hanging circuit in the RF admittance type to solve the problem of emergency signal misoperation caused by the susceptibility of capacitive type to hanging materials.
The RF admittance level switch is composed of a balanced bridge circuit formed by the reactance between the probe measuring electrode and the empty tank body, and generates a stable oscillation signal. When the measured medium covers the probe measuring electrode, the oscillation signal stops, and the subsequent circuit detects this change and outputs an emergency signal to start. A stable oscillation signal is applied as an RF signal to the measuring electrode of the probe, and is also sent to the protective electrode of the probe through a 1:1 voltage follower structure in the internal circuit. At this time, the RF signals of the measuring electrode and the protective electrode have the characteristics of equal potential, same phase, same frequency, and mutual isolation. When there is a hanging material on the probe, the RF admittance level switch forms electrical isolation between the measuring electrode and the protective electrode due to the absence of potential difference, ensuring that the signal change of the protective electrode does not affect the detection, so that the change in reactance on the measuring electrode of the probe can only be determined by the material between the measuring electrode of the probe and the tank body, so that the hanging material on the probe will not affect normal detection.
Due to the lack of a 1:1 voltage follower circuit structure, the capacitive level switch also lacks a protective electrode between the probe measuring electrode and the tank body. When there is a hanging material on the probe, there is no potential isolation between the measuring electrode and the tank body. The reactance of the adhered material on the measuring electrode of the probe will directly affect the detection, resulting in the occurrence of emergency signal misoperation of the probe.
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