Process Engineering Division – Instrumentation and Automation Section – Daily Question – Question from 2020-10-15

Working principle: The structure of the radio frequency admittance level gauge consists of a main electrode and a compensation electrode. A set of RF signals is applied between the main electrode and the compensation electrode, which gives it excellent resistance to sticking and adhesion of materials; it is a new type of level measurement device for solids/liquids that can replace capacitive level switches. Due to the presence of the guard electrode, the detection circuit compares the signals from the detection electrode and the guard electrode, thereby overcoming the impact of material adhesion on level measurement. Features: 1. High versatility: Suitable for various applications, capable of detecting particles, fly ash, conductive and non-conductive liquids, as well as viscous materials; 2. Anti-adhesion circuit: An advanced anti-adhesion circuit design that prevents material adhesion from causing false error signals; 3. Power loss protection mode: Alerts in the event of low or high level faults. Adjustable on-site. 4. Easy to install and adjust. 5. Not affected by sticking or clinging of materials. 6. Good stability, unaffected by temperature. 7. Delayed output can be adjusted. 8. Optional temperature resistance up to 550°C. 9. Failure protection functions for high and low positions

RF admittance is a new type of level control technology that evolved from capacitive technology; it prevents material accumulation, offers greater reliability and accuracy, and has a wider range of applications – representing an upgrade to capacitive level control techniques. The so-called radio frequency admittance refers to the reciprocal of impedance in electricity; it is composed of resistive, capacitive, and inductive components. Since radio frequency denotes the high-frequency portion of the radio wave spectrum, radio frequency admittance can be understood as the measurement of admittance using high-frequency radio waves. When the instrument is in operation, its sensors form an admittance value with the wall of the tank and the medium being measured. As the liquid level changes, this admittance value changes accordingly; the circuit unit converts this measured admittance value into a liquid level signal, thereby enabling the measurement of the liquid level. For continuous measurement, in addition to the differences mentioned above between radio frequency admittance technology and traditional capacitance technology, two very important circuits have been added; these were developed based on an important discovery from practical experience with conductive materials. The aforementioned technology also solved the problem of connection cables at this time, as well as the issue of material accumulation at the base of sensors installed vertically. The two additional circuits added to the lock are an oscillator buffer and an AC conversion chopper driver. For a container holding a highly conductive medium under test, since the medium is conductive, the ground point can be considered to be at the surface of the probe’s insulating layer; for the transmitter, this results in a pure capacitance. As the container is discharged, material accumulates on the probe, and this accumulated material has impedance. In this way, the previous pure capacitor now becomes a complex impedance composed of a capacitor and a resistor, thereby causing two problems.

Working principle: The structure of the radio frequency admittance level gauge consists of a main electrode and a compensation electrode. A set of RF signals is applied between the main electrode and the compensation electrode, which gives it excellent resistance to sticking and adhesion of materials; it is a new type of level measurement device for solids/liquids that can replace capacitive level switches. Due to the presence of the guard electrode, the detection circuit compares the signals from the detection electrode and the guard electrode, thereby overcoming the impact of material adhesion on level measurement. Features: 1. High versatility: Suitable for various applications, capable of detecting particles, fly ash, conductive and non-conductive liquids, as well as viscous materials; 2. Anti-adhesion circuit: An advanced anti-adhesion circuit design that prevents material adhesion from causing false error signals; 3. Power loss protection mode: Alerts in the event of low or high level faults. Adjustable on-site. 4. Easy to install and adjust. 5. Not affected by sticking or clinging of materials. 6. Good stability, unaffected by temperature. 7. Delayed output can be adjusted. 8. Optional temperature resistance up to 550°C. 9. Failure protection functions for high and low positions

RF admittance is a new type of level control technology that evolved from capacitive technology; it prevents material accumulation, offers greater reliability and accuracy, and has a wider range of applications – representing an upgrade to capacitive level control techniques. The so-called radio frequency admittance refers to the reciprocal of impedance in electricity; it is composed of resistive, capacitive, and inductive components. Since radio frequency denotes the high-frequency portion of the radio wave spectrum, radio frequency admittance can be understood as the measurement of admittance using high-frequency radio waves. When the instrument is in operation, its sensors form an admittance value with the wall of the tank and the medium being measured. As the liquid level changes, this admittance value changes accordingly; the circuit unit converts this measured admittance value into a liquid level signal, thereby enabling the measurement of the liquid level. For continuous measurement, in addition to the differences mentioned above between radio frequency admittance technology and traditional capacitance technology, two very important circuits have been added; these were developed based on an important discovery from practical experience with conductive materials. The aforementioned technology also solved the problem of connection cables at this time, as well as the issue of material accumulation at the base of sensors installed vertically. The two additional circuits added to the lock are an oscillator buffer and an AC conversion chopper driver. For a container holding a highly conductive medium under test, since the medium is conductive, the ground point can be considered to be at the surface of the probe’s insulating layer; for the transmitter, this results in a pure capacitance. As the container is discharged, material accumulates on the probe, and this accumulated material has impedance. In this way, the previous pure capacitor now becomes a complex impedance composed of a capacitor and a resistor, thereby causing two problems.

RF admittance is a new type of level control technology that evolved from capacitive technology; it prevents material accumulation, offers greater reliability and accuracy, and has a wider range of applications – representing an upgrade to capacitive level control techniques. The so-called radio frequency admittance refers to the reciprocal of impedance in electricity; it is composed of resistive, capacitive, and inductive components. Since radio frequency denotes the high-frequency portion of the radio wave spectrum, radio frequency admittance can be understood as the measurement of admittance using high-frequency radio waves. When the instrument is in operation, its sensors form an admittance value with the wall of the tank and the medium being measured. As the liquid level changes, this admittance value changes accordingly; the circuit unit converts this measured admittance value into a liquid level signal, thereby enabling the measurement of the liquid level. For continuous measurement, in addition to the differences mentioned above between radio frequency admittance technology and traditional capacitance technology, two very important circuits have been added; these were developed based on an important discovery from practical experience with conductive materials. The aforementioned technology also solved the problem of connection cables at this time, as well as the issue of material accumulation at the base of sensors installed vertically. The two additional circuits added to the lock are an oscillator buffer and an AC conversion chopper driver. For a container holding a highly conductive medium under test, since the medium is conductive, the ground point can be considered to be at the surface of the probe’s insulating layer; for the transmitter, this results in a pure capacitance. As the container is discharged, material accumulates on the probe, and this accumulated material has impedance. In this way, the previous pure capacitor now becomes a complex impedance composed of a capacitor and a resistor, thereby causing two problems.

I did ask the manufacturer some time ago; radio frequency admittance is essentially an upgraded version of capacitors, and the measurement signals are stable

This part covers the principles of radio frequency admittance; it would be perfect if the differences between the principles and applications were also outlined.

This section is explained very well, but it seems like something is left unfinished.

The first issue is that the liquid level itself acts as a capacitor for the probe; it does not consume any energy from the transmitter (a pure capacitor does not consume energy). However, since the load introduces resistances in the equivalent circuit of the probe, the impedance of the load consumes energy, which in turn lowers the voltage of the oscillator. This causes a change in the output of the bridge circuit, resulting in measurement errors. We added a buffer amplifier between the oscillator and the bridge to replenish the energy consumed, thereby preventing a decrease in the oscillating voltage applied to the probe. The second issue is that, for conductive test media, the grounding point on the surface of the probe’s insulating layer covers the entire test medium as well as the area where the material is held, thereby extending the effective measurement capacitance to the top of that material. This results in a loading error, and the greater the conductivity, the larger the error. However, no medium under test is completely conductive. From an electrical perspective, the coating layer acts as a resistor, while the part of the sensing element that is covered by the coating corresponds to a transmission line composed of countless infinitesimally small capacitive and resistive elements. According to mathematical theory, if the hanging element is long enough, the impedance of its capacitive and resistive components is equal. Therefore, based on the study of the errors caused by the load impedance, an additional AC driver circuit was added. This circuit, together with an AC converter or a synchronous detector, can measure capacitance and resistance separately, thereby eliminating the influence of residual material.

Working principle: The structure of the radio frequency admittance level gauge consists of a main electrode and a compensation electrode. A set of RF signals is applied between the main electrode and the compensation electrode, which gives it excellent resistance to sticking and adhesion of materials; it is a new type of level measurement device for solids/liquids that can replace capacitive level switches. Due to the presence of the guard electrode, the detection circuit compares the signals from the detection electrode and the guard electrode, thereby overcoming the impact of material adhesion on level measurement. Features: 1. High versatility: Suitable for various applications, capable of detecting particles, fly ash, conductive and non-conductive liquids, as well as viscous materials; 2. Anti-adhesion circuit: An advanced anti-adhesion circuit design that prevents material adhesion from causing false error signals; 3. Power loss protection mode: Alerts in the event of low or high level faults. Adjustable on-site. 4. Easy to install and adjust. 5. Not affected by sticking or clinging of materials. 6. Good stability, unaffected by temperature. 7. Delayed output can be adjusted. 8. Optional temperature resistance up to 550°C. 9. Failure protection functions for high and low positions