Description of the types, principles, advantages and disadvantages of the level gauge

Magnetic float level gauge
Developed according to the principle of buoyancy and magnetic coupling. When the liquid level in the measured container rises and falls, the magnetic float in the body tube of the liquid level gauge also rises and falls, and the permanent magnetic steel in the float is transmitted to the magnetic flip column indicator through magnetic coupling, and the red and white flip columns are turned over. When the liquid level rises, the column changes from white to red. When the liquid level drops, the column changes from red to white, and the red-white junction of the indicator is the actual height of the liquid level inside the container, thus achieving a clear indication of the liquid level.
It can be highly sealed, leakproof and suitable for high temperature, high pressure and corrosion resistance. It is superior to high temperature, high pressure, toxic, harmful and strong corrosive media.
Direct contact with the medium, the requirements of the float ball seal are strict, and the viscous medium cannot be measured. Magnetic materials such as demagnetization tend to cause the level gauge to not work properly.
Magnetic flap (column) level gauge
With the same
With the same
The flap is easily stuck, making it impossible to pass the instructions. Magnetic materials such as demagnetization tend to cause the level gauge to not work properly.
Electromagnetic wave radar level gauge (guided wave radar level gauge)
The radar level gauge uses a transmit-reflection-receive mode of operation. The antenna of the radar level gauge emits electromagnetic waves. These waves are reflected by the surface of the object to be measured and then received by the antenna. The time from the transmission to the reception of the electromagnetic wave is proportional to the distance from the liquid surface. The relationship is as follows:
D=CT/2
(D: distance from radar level gauge to liquid level C: speed of light T: electromagnetic wave running time)
The radar level gauge records the time elapsed by the pulse wave, and the electromagnetic wave transmission speed is constant, then the distance from the liquid surface to the radar antenna can be calculated to know the liquid level of the liquid surface.
It does not need to transmit media, and is not affected by atmospheric, vapor, and volatilization in the tank. It can be used for liquid level measurement of volatile media. Non-contact measurement is not affected by physical properties such as density and concentration of liquid in the tank.
expensive. The instrument needs to set more parameters. Once a problem occurs, it is often difficult to find out what caused it. If the antenna itself accidentally gets on the media, it will report an error. If there is crystal icing, it will report an error, heat and heat treatment, and clean the antenna. The initial installation needs to be an empty position, that is, an empty level?
Ultrasonic level gauge
The ultrasonic level gauge is a digital level meter controlled by a microprocessor. In the measurement, the pulsed ultrasonic wave is emitted by the sensor (transducer), and the sound wave is reflected by the surface of the object and received by the same sensor to be converted into an electrical signal. The distance from the sensor to the measured object is calculated from the time between the transmission and reception of the sound wave.
No mechanical movable parts, high reliability, simple and convenient installation, non-contact measurement, and not affected by viscosity, density, etc. of liquid
The accuracy is relatively low, and the test is prone to blind spots. Pressure vessels cannot be measured and volatile media cannot be measured.
Capacitive level gauge
The change in capacitance is measured to measure the level of the liquid surface. It is a metal rod inserted into a liquid container, the metal rod acts as a pole of the capacitor, and the wall of the container acts as the other pole of the capacitor. The medium between the two electrodes is the liquid and the gas above it. Since the dielectric constant ε1 of the liquid and the dielectric constant ε2 on the liquid surface are different, for example, ε1 ε2, when the liquid level rises, the total dielectric constant value between the two electrodes increases and the capacitance increases. . Conversely, as the liquid level drops, the ε value decreases and the capacitance decreases. Therefore, the level of the liquid level can be measured by the change in capacitance between the two electrodes. The sensitivity of the capacitance level gauge depends mainly on the difference between the two dielectric constants. Moreover, only the constant ε1 and ε2 can ensure the accurate measurement of the liquid level. Because the measured medium has conductivity, the metal rod electrode has an insulating layer covering. .
The sensor has no mechanical movable parts, the structure is simple and reliable; the precision is high; the detecting end consumes small electric energy, the dynamic response is fast; the maintenance is convenient and the service life is long. The measured medium needs to be an amorphous conductive liquid having a conductivity of not less than 10-3 S/M.
Unstable dielectric constant of the liquid being tested can cause errors. Capacitive level gauges are commonly used to regulate pools and clear water tanks. (Note: Whether liquefied gas will affect the measurement is unknown.)
Static pressure (differential pressure) type liquid level gauge
Since the static pressure of the liquid column is proportional to the liquid level, the liquid level can be measured by measuring the static pressure of the liquid column on the reference surface using a pressure gauge. Calculate the pressure or differential pressure range according to the density of the measured medium and the liquid measurement range, and then select a pressure gauge or differential pressure gauge with appropriate performance such as range and accuracy.
Wide range of applications and easy to calibrate.
Due to the large density and temperature of the medium, the accuracy is often poor. To eliminate these effects, many other test instruments are needed. As a result, a complete static pressure measurement system is expensive.
Magnetostrictive level gauge
The upper part of the probe generates a low-voltage current pulse, starts timing, and generates a magnetic field that propagates down the magnetostrictive line. The float moves up and down along the measurement 随着 as the liquid level changes. There is a magnet in the float, and a magnetic field is generated, and the two magnetic fields meet. The magnetostrictive wire is twisted to form a torsional stress wave pulse, and the pulse velocity is known. The pulse propagation time is calculated to correspond to the accurate change of the liquid level.
High precision. Suitable for oily liquids.
Installation and maintenance are complicated and the market penetration rate is low. (Note: pulse principle, suspected also has the disadvantage of radar level gauge)