Radio frequency admittance level meter

Radiofrequency Admittance Level Meter is widely used for continuous measurement of the level of liquid, particle and block material silos in various industries. Suitable for high temperature, high pressure, strong corrosion, strong adhesion, strong impact, strong wear, dust under the environment of measurement, there are other types of level meter incomparable cost performance. The product is used in the field of industry and mining, suitable for most applications, the instrument is composed of a circuit unit, a set of explosion-proof shell and rod or cable type sensing components, the sensor has a variety of models can be selected, the instrument can be selected as a whole or separate installation.

Measuring principle of RF admittance level meter:

RF admittance is a new level control technology developed from capacitive type, which is more reliable, more accurate and more applicable. It is an upgrade of capacitive level technology. The so-called RF admittance means the reciprocal of impedance in electricity, which is composed of resistive component, capacitive component and inductive component. RF is the high frequency radio spectrum, so RF admittance can be understood as the measurement of admittance with high frequency radio waves. When the instrument is working, the sensor of the instrument forms the admittance value with the wall and the medium to be measured. When the level changes, the admittance value changes correspondingly. The circuit unit will convert the measured admittance value into the level signal output to realize the level measurement.

For continuous measurement, the difference between RF admittance technology and traditional capacitance technology is not only described above, but also adds two very important circuits, which are improved based on a very important discovery made in the practice of conductive pincers. The above technology also solves the problem of connecting the cable, and also solves the problem of hanging the root of the vertically mounted sensor. The two circuits added to the lock are the oscillator buffer and the AC transform chopper driver.

For a container with strong conductivity of the medium under test, since the medium under test is conductive, the connection point can be considered on the surface of the probe insulation layer and will only represent a pure capacitance for the transmitter. As the container is discharged, the rod is hung, which has an impedance. The previously pure capacitance is now a complex impedance composed of capacitance and resistor, causing two problems.

The first problem is that the liquid level itself acts as a capacitor to the probe, which does not consume the power of the transmitter (pure capacitors do not consume energy). But there is resistance in the equivalent circuit of the probe, so the impedance of the hanging material will consume energy, which will pull down the oscillator voltage, resulting in the change of the bridge output, resulting in measurement error. We add a buffer amplifier between the oscillator and the bridge, so that the energy consumption is replenished, so that the oscillation voltage applied to the probe will not be reduced.

The second problem is that for the conductive medium to be measured, the contact point on the surface of the probe insulation layer covers the whole medium to be measured and the hanging area, so that the effective measurement capacitor is extended to the top of the hanging material. This will produce the error of hanging material, and the stronger the conductivity error. But no medium under test is completely conductive. From the 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 capacitor and resistor elements. According to mathematical theory, if the hanging material is long enough, the capacitance of the hanging material and the impedance of the resistance part are equal. Therefore, according to the study of the error caused by the hanging impedance, another AC driver circuit is added. The circuit can be used together with AC converter or synchronous detector to measure capacitance and resistance respectively. Since the impedance and capacitance of the hanging material are equal, the total capacitance measured is equivalent to C+C hanging material. Subtracting the resistance R equal to C hanging material, the real value can be actually measured, thus excluding the effect of hanging material.

That is, C measurement =C+C hanging material

C=C measurement - C hanging material

=C measurement -- R

These, multi-parameter measurement, is the necessary basis, AC phase discrimination sampler is the means to achieve. Because of the use of the above three technologies, the RF admittance technology has shown extraordinary vitality in field application.

Features of RF admittance level meter:

Calibration is simple: you can use any two point warehouse height to complete the calibration automatically.

Strong versatility: can measure the liquid level and material level, can meet the different temperature, pressure, medium measurement requirements, and can be applied to corrosion, impact and other bad occasions.

Anti-hanging material: the unique circuit design and sensor structure, so that the measurement can not be affected by the sensor hanging material, no need to clean regularly, to avoid mismeasurement.

Maintenance-free: there are no moving parts in the measurement process, no mechanical parts are damaged, no maintenance required.

Anti-dry disturbance: contact measurement, strong anti-interference ability, can overcome the influence of steam, foam and stirring on the measurement.

Widely used: liquid, solid, interface mixture, materials can be used.

No drift: no drift due to changes in temperature or density of the medium.

Accurate and reliable: the measurement quantity is diversified, so that the measurement is more accurate, Zeliang is not affected by environmental changes, high stability, long service life.

Liquid crystal display: the use of liquid crystal display, display content is rich and comprehensive.

Typical applications of RF admittance level meter:

Conducting and insulating liquid ………… Chemical industry, oil field, water and sewage treatment

Conductive and insulating slurry ………… Paper making, pharmaceutical, water and sewage treatment

Powder: ash, powder …………… Power plant, metallurgy, cement

Particle: coal, food ………… Power plant, metallurgy, grain

Interface: Two different liquids... Oil field, chemical industry

Performance indicators of RF admittance level meter:

Power supply: 18 v - 30 VDC

Spark protection (to sensors) : built-in spark protection circuit

Lost: 4-20 ma

Electrical interface: M20×1.5

Output mode: level mode or distance mode

Cable: special connection cable between split type electronic unit and sensor is standard 5m, length 50m

Fineness: ±0.5% ±0.2%

Ambient temperature: -40℃ ~ 70℃

Process connection: NPT thread mounting (standard)

Medium temperature: -100℃ ~ 260℃

Flange installation :(optional)

Load: 24VDC 350Ω

Enclosure protection: IP66

Load impact: 0.2%

Explosion-proof: Exid Ⅱ CT4

Response time: 0.5S (table) 0.5 ~ 30s (adjustable)

Range: 15000pF, distance: 100m (different sensor range is different)