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March 16, 2020
RF admittance level switches and capacitive level switches are two common level switches. From the appearance, the RF admittance probe is composed of three layers of metal: measuring electrode, protective electrode and tank electrode, while the capacitive probe is composed of two layers of metal: measuring electrode and tank electrode. The difference in the structure of the above probes is because the RF admittance type adds an anti-feeding circuit that solves the problem of capacitive alarms that are susceptible to hanging materials and false alarms.
The RF admittance level switch is composed of the reactance between the probe measuring pole and the no-load tank to form a balanced bridge circuit and generate a stable oscillation signal. When the measured medium covers the probe measuring pole, the oscillation signal stops and the subsequent circuit detects this. A change thereby outputs an alarm signal. When the stable oscillation signal is applied as the RF signal to the probe's measuring pole, it is also sent to the probe's protective pole through the 1: 1 voltage follower structure in the internal circuit. At this time, the radio frequency signal of the measuring pole and the protective pole have the same potential and the same Phase, same frequency and isolated from each other. When there is hanging material on the probe, there is no electrical potential difference between the measuring electrode of the RF admittance level switch and the protection electrode to form electrical isolation, to ensure that the signal change of the protection electrode does not affect the detection. The material between the measuring pole of the probe and the tank is determined so that the hanging material on the probe will not affect the normal detection.
Because of the lack of 1: 1 voltage follower circuit structure of the capacitive level switch, the protective pole is also missing between the measuring pole of the probe and the tank. When the probe is hanging, there is no potential isolation between the measuring electrode and the tank. The reactance of the material adhered to the measuring electrode of the probe will directly affect the detection, which will cause a false alarm of the probe.
Field practice proves that the RF admittance level switch is developed from a capacitive level switch and is a level control product that is anti-hanging, more reliable, and more applicable.