I. Overview and measurement principle:
是一种从电容式发展起来的、防挂料、更可靠、更准确、适用性更广的新型物位控制技术，是电容式物位技术的升级。 RF admittance is a new level control technology developed from capacitive, anti-hanging material, more reliable, more accurate, and more applicable. It is an upgrade of capacitive level technology. The so-called RF admittance means the inverse of impedance in electricity. It is a combination of resistive, capacitive, and inductive components, and radio frequency is the high-frequency radio spectrum, so RF admittance can be understood as using high-frequency Radio wave measurement of admittance. When the meter is working, the sensor of the meter forms an admittance value with the wall and the measured medium. When the level changes, the admittance value changes accordingly. The circuit unit converts the measured admittance value into a level signal output to achieve level measurement.
技术与传统电容技术的区别除了上述讲过的以外，还增加了两个很重要的电路，这是根据导电挂料实践中的一个很重要的发现改进而成的。 For continuous measurement, the difference between the RF admittance technology and the traditional capacitor technology, in addition to the above, also adds two very important circuits, which are improved based on an important discovery in the practice of conductive materials. The above-mentioned technology also solves the problem of connecting cables at this time, and also solves the problem of hanging materials 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 strong conductive test medium, the ground point can be considered as the surface of the probe insulation layer because the test medium is conductive, and it appears as a pure capacitor to the transmitter. As the container is discharged, hanging material is generated on the probe, and the hanging material has resistance. In this way, the former pure capacitor has now become a complex impedance composed of a capacitor and a resistor, causing two problems.
The first problem is that the liquid level itself is equivalent to a capacitor to the probe, which does not consume the energy of the transmitter (pure capacitors do not consume energy). However, the resistance of the hanging material to the probe equivalent circuit will consume energy, which will pull down the voltage of the oscillator, which will cause the output of the bridge to change and cause measurement errors. We have added a buffer amplifier between the oscillator and the bridge so that the energy consumed is replenished, so the oscillation voltage applied to the probe is not reduced.
The second problem is that for the conductive test medium, the ground point on the surface of the probe insulation layer covers the entire test medium and the hanging area, so that the effective measurement capacitance is extended to the top of the hanging material. This results in hanging errors, and the greater the conductivity, the greater the error. But any measured medium 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 material is long enough, the capacitance of the material and the resistance of the material are equal. Therefore, according to the study of the error caused by the impedance of the hanging material, another AC driver circuit is added. Together with an AC converter or a synchronous detector, this circuit can measure capacitance and resistance separately. Because the impedance and capacitive reactance of the hanging material are equal, the measured total capacitance is equivalent to C + C hanging material, and then subtracting the resistance R equal to C hanging material, the actual value can be actually measured, thereby excluding the influence of hanging material.
That is C measurement = C + C hanging material
C = C measurement—C hanging material
= CMeasurement — R
These, multi-parameter measurements, must be based, and the AC phase detector sampler is the means to achieve it. 技术在现场应用中展现出非凡的生命力。 Due to the use of the above three technologies, RF admittance technology has demonstrated extraordinary vitality in field applications.
1. Strong versatility: can measure liquid level and material level, can meet the measurement requirements of different temperatures, pressures and media, and can be used in harsh environments such as corrosion and impact;
2. Anti-hanging material: The unique circuit design and sensor structure make its measurement not affected by the hanging material of the sensor, without regular cleaning and avoiding false measurement.
3. Maintenance-free: There are no moving parts in the measurement process, no mechanical parts are damaged, and no maintenance is required.
4. Anti-interference: contact measurement, strong anti-interference ability, can overcome the influence of steam, foam and stirring on the measurement.
5. Accurate and reliable: The measurement volume is diversified, making the measurement more accurate. Zeliang is not affected by environmental changes, has high stability, and has a long service life.