Overview of radio frequency admittance level meter
Mat700 series is a general-purpose RF admittance level meter, which is used for continuous level measurement. The product is applied to industrial and mining sites and suitable for most applications. The instrument is composed of a circuit unit, a set of explosion-proof enclosure and rod or cable type sensing elements. There are many types of sensors, and the instrument can be installed in whole or separately
Overview of RF admittance level meter
Radio frequency admittance is a new material level control technology developed from capacitance, which is more reliable, more accurate and more applicable. It is an upgrade of capacitive level technology. The so-called radio frequency admittance means the reciprocal of impedance in electricity. It is composed of resistive component, capacitive component and inductive component. Radio frequency is the spectrum of high-frequency radio wave, so RF admittance can be understood as measuring admittance with high-frequency radio wave. When the instrument works, the sensor of the instrument forms the admittance value with the filling wall and the measured medium. When the material level changes, the admittance value changes correspondingly. The circuit unit converts 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 mentioned above, but also two very important circuits, which are improved according to a very important discovery in the practice of conductive hanging materials. At this time, the above technology also solves the problem of connecting cable and hanging material at the root of vertical sensor. The two circuits added to the lock are oscillator buffer and AC converter chopper driver.
For a container with strong conductivity, because the measured medium is conductive, the grounding point can be regarded as on the surface of the probe insulation layer, which is only a pure capacitance for the transmitter. With the discharge of the container, there is a hanging material on the probe rod, and the hanging material has impedance. In this way, the former pure capacitance is now a complex impedance composed of capacitance and resistance, which causes 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 impedance of the hanging material will consume energy, which will pull down the oscillator voltage, resulting in the change of the bridge output and the measurement error. We add a buffer amplifier between the oscillator and the bridge to supplement the energy consumed, so that the oscillation voltage added to the probe will not be reduced.
The second problem is that for the conductive measured medium, the grounding point on the surface of the probe insulation layer covers the whole measured medium and hanging area, so that the effective measurement capacitance extends to the top of the hanging material. In this way, there will be hanging error, and the stronger the conductivity, the greater the error. However, any measured medium is not fully conductive. From the electrical point of view, the hanging layer is equivalent to a resistance, and the sensing element covered by the hanging material is equivalent to a transmission line composed of countless infinitesimal capacitance and resistance elements. According to the mathematical theory, if the hanging material is long enough, the capacitance and resistance of the hanging material are equal. Therefore, according to the error research of hanging material impedance, an AC driver circuit is added. The circuit can measure capacitance and resistance separately with AC converter or synchronous detector. Since the impedance and capacitance reactance of the hanging material are equal, the measured total capacitance is equivalent to the C + c hanging material, and then the resistance r equal to the c hanging material can be subtracted to actually measure the real value, so as to eliminate the influence of the hanging material.
That is, C measurement = C + c hanging material
C = C measurement - c hanging
= C measurement - R
These, multi parameter measurement, is necessary foundation, AC phase detector sampler is the means of realization. Due to the use of the above three technologies, the RF admittance technology shows extraordinary vitality in the field application.
Performance index of radio frequency admittance level meter
Power supply: 18v-30vdc spark protection (for sensor): built-in spark protection circuit
Output: 4-20mA; electrical interface: M20 × 1.5
Output mode: material level mode or distance mode cable: special connection precision between split electronic unit and sensor: ± 1% ± 0.5% cable connection standard 5m, long 50m
Ambient temperature: - 40 ℃ ~ 70 ℃ process connection: NPT thread installation (standard)
Medium temperature: - 100 ℃ ~ 260 ℃ flange installation (optional)
Protection: 350 Ω
Load influence: 0.2% (0 -- large load) explosion proof: exid Ⅱ cT4
Response time: 0.5s (surface) 0.5-30s (adjustable)
Range: larger 15000pf, larger distance 100m (different sensors with different ranges)
|| Continuous level meter
|| Power Supply
|| 24 VDC two wire system
|| Scope of application
|| Ordinary medium
|| Strong conductive medium
|| Mode of action
|| Level mode
|| Distance mode
|| See mat700 sensor selection table
| Installation mode
|| Integral installation
|| Split installation
Strong versatility: it can measure liquid level and material level, meet the measurement requirements of different temperature, pressure and medium, and can be used in harsh occasions such as corrosion and impact
Anti hanging material: the unique circuit design and sensor structure make the measurement can be free from the influence of sensor hanging material, without regular cleaning, to avoid wrong measurement.
Maintenance free: there are no movable parts in the measurement process, and there is no damage problem of mechanical parts, so maintenance is not required.
Anti interference: contact measurement, strong anti-interference ability, can overcome the influence of steam, foam and stirring on the measurement.
Good quality, long service life and high accuracy.
Typical application of radio frequency admittance level meter
Conductive and insulating liquids Chemical industry, oil field, water and sewage treatment
Conductive and insulating paste Papermaking, pharmacy, water and sewage treatment
... powder Power plant, metallurgy, cement
Grain: coal, grain Power plant, metallurgy, grain
Interface: two different liquids Oil field, chemical industry