Measurement principle of radio frequency admittance level gauge

What is the measurement principle of the RF admittance level gauge? RF admittance is an upgrade of capacitive level technology. The so-called radio frequency admittance means the inverse of the impedance in electricity. It is composed of resistive components, capacitive components, and inductive components, and radio frequency is the high-frequency radio spectrum. Therefore, radio frequency admittance can be understood as the use of high frequency. Radio waves measure admittance. When the meter is working, the sensor of the meter forms an admittance value with the filling wall and the measured medium. When the material level changes, the admittance value changes accordingly, and the circuit unit converts the measured admittance value into a level signal output to realize the level measurement. For continuous measurement, the difference between the radio frequency admittance technology and the traditional capacitance technology, in addition to the above mentioned, also adds two very important circuits, which are improved according to a very important discovery in the practice of conductive hanging materials. The above technology also solves the problem of connecting cables at this time, and also solves the problem of hanging material at the root of the vertically installed sensor. The two circuits added to the lock are the oscillator buffer and the AC conversion chopper driver. For a container with a strongly conductive medium to be measured, since the medium to be measured is conductive, the grounding point can be considered to be on the surface of the insulating layer of the probe, and only appears as a pure capacitance to the transmitter. As the container discharges, material hangs on the probe rod, and the hanging material has resistance. In this way, what used to be pure capacitance is now a complex impedance consisting of capacitance and resistance, causing two problems. The first problem is that the liquid level itself is equivalent to a capacitance to the probe, which does not consume the energy of the transmitter (pure capacitance does not consume energy). However, if there is resistance in the equivalent circuit of the hanging material to the probe, the resistance of the hanging material will consume energy, thereby pulling down the oscillator voltage, resulting in a change in the bridge output, resulting in measurement errors. We added a buffer amplifier between the oscillator and the bridge to supplement the dissipated energy without reducing the oscillating voltage applied to the probe. The second problem is that for the conductive measured medium, the grounding point on the surface of the insulating layer of the probe covers the entire measured medium and the hanging material area, so that the effective measurement capacitance extends to the top of the hanging material. In this way, a hanging error occurs, and the stronger the conductivity, the greater the error. But no measured medium is fully conductive. From an electrical point of view, the hanging layer is equivalent to a resistor, and the part of the sensing element covered by the hanging material is equivalent to a transmission line composed of countless infinitesimal capacitance and resistance elements. According to mathematical theory, if the hanging material is long enough, the impedance of the capacitance and resistance parts of the hanging material is equal. Therefore, according to the research on the error caused by the hanging material impedance, another AC driver circuit is added. Together with an AC converter or a synchronous detector, this circuit can measure capacitance and resistance, respectively. Since the impedance and capacitive reactance of the hanging material are equal, the total capacitance measured is equivalent to the C+C hanging material, and then subtracting the resistance R equal to the C hanging material, the actual value can be measured, thereby eliminating the influence of the hanging material. That is, C measurement = C + C hanging C = C measurement - C hanging = C measurement - R
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