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Industry Information
Difference between RF admittance level switch and capacitive level switch
2012-3-1 10:02:37

控制技术是一种从电容式物位控制技术发展起来的,防挂料、更可靠、更准确、适用性更广的物位控制技术,“射频导纳”中“导纳”的含义为电学中阻抗的倒数,它由阻性成分、容性成分、感性成分综合而成,而“射频”即高频,所以射频导纳技术可以理解为用高频测量导纳。 RF admittance level switch control technology is a kind of level control technology developed from capacitive level control technology. It is anti-hanging material, more reliable, more accurate and more applicable. The meaning of "admittance" is the inverse of impedance in electricity. It is a combination of resistive, capacitive, and inductive components, and "radio frequency" is high frequency, so RF admittance technology can be understood as measuring admittance with high frequency. The high-frequency sine oscillator outputs a stable measurement signal source, using the principle of electric bridge to accurately measure the admittance of the sensor installed in the container to be measured. In the direct-acting mode, the output of the meter increases with the level of the material. increase.

The difference between RF admittance technology and traditional capacitor technology lies in the diversity of measurement parameters, driving three-terminal shielding technology, and the addition of two important circuits, which are improved based on valuable experience in practice. The two added circuits are a high-precision oscillator driver and an AC phase detector sampler.

For a container with strong conductive material, the ground point can be considered as the surface of the probe insulation layer because the material is conductive. For the transmitter probe, it only appears as a pure capacitor. Hanging material is produced, and the hanging material has impedance. In this way, the former pure capacitor has now become a complex impedance composed of a capacitor and a resistor, causing two problems.

技术由于引入了除电容以外的测量参量,尤其是电阻参量,使得仪表测量信号信噪比上升,大幅度地提高了仪表的分辨力、准确性和可靠性:测量参量的多样性也有力地拓展了仪表的可靠应用领域。 The RF admittance level switch technology introduces measurement parameters other than capacitance, especially resistance parameters, which increases the signal-to-noise ratio of the measurement signal of the instrument, greatly improving the resolution, accuracy and reliability of the instrument: Diversity also strongly expands the reliable application field of the instrument.

The first problem is that the material itself is equivalent to a capacitor to the probe, it does not consume the energy of the transmitter, (pure capacitor does not consume energy), but the resistance of the hanging material will be consumed if the hanging material has resistance in the probe equivalent circuit. Energy, which pulls down the oscillator voltage, causing the bridge output to change, causing measurement errors. We have added a driver between the oscillator and the bridge to supplement the energy consumed, thus stabilizing the oscillation voltage applied to the probe.

The second problem is that for conductive materials, the ground point on the surface of the probe insulation layer covers the entire material and the hanging material area, so that the effective measuring capacitance is extended to the top of the hanging material. This will cause hanging material errors, and the more conductive the error, Big. But any material is not completely conductive. From an electrical point of view, the hanging material 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 infinitely small capacitors and resistance elements. According to mathematical theory, if the hanging material is long enough, the impedance and capacitance values of the capacitance and resistance parts of the hanging material are equal, so the AC phase detector sampler can measure the capacitance and resistance, respectively.

RF admittance can completely replace capacitors. For switches, the difference between RF admittance and capacitance is obvious. Capacitance probes are two electrodes, and admittance probes are three electrodes. A shielded protective electrode is added between the measurement electrode and ground. The corresponding circuit is also the same, the added shielding protection poles play the role of anti-hanging material, so the appearance and the capacitance can be distinguished.

比电容抗挂料会有很大提高。 For the switch, there are special designs from the probe to the circuit, so the RF admittance level switch will greatly improve the anti-hanging capacity of the capacitor. For continuous quantities, the admittance and capacitance probes are the same, so they are indistinguishable from their appearance. The main difference between the two is the circuit. Two circuits are added to the admittance, the oscillation drive and the AC sampling circuit. The improvement of the admittance in the circuit to achieve anti-hanging material and improve stability.