1. Magnetic float level gauge

(1) Principle:

When the liquid level in the measured container rises or falls, the magnetic float in the main tube of the level gauge also rises or falls. The permanent magnet in the float is transmitted to the magnetic flip column indicator through magnetic coupling, driving the red and white flip columns to flip. When the liquid level rises, the flip column changes from white to red, and when the liquid level drops, the flip column changes from red to white. The red and white intersection of the indicator is the actual height of the liquid level inside the container, thereby achieving a clear indication of the liquid level.

(2) Advantages:

It can achieve high sealing, anti-leakage and is suitable for high temperature, high pressure and corrosion-resistant occasions. It is more superior for high temperature, high pressure, toxic, harmful and highly corrosive media.

(3) Disadvantages:

It is in direct contact with the medium, the float ball sealing requirements are strict, and it cannot measure viscous media. Magnetic materials such as demagnetization can easily cause the level gauge to not work properly.

2. Magnetic flap (column) level gauge

(1) Principle:

Same as magnetic float level gauge.

(2) Advantages:

Same as magnetic float level gauge.

(3) Disadvantages:

The flap is easily stuck, resulting in the inability to transmit indication remotely. If the magnetic material is demagnetized, it is easy to cause the level gauge to not work properly.

3. Electromagnetic wave radar level meter (guided wave radar level meter)

(1) Principle:

The radar level meter adopts the transmission-reflection-reception working mode. The antenna of the radar level meter emits electromagnetic waves, which are reflected by the surface of the measured object and then received by the antenna. The time from the emission to the reception of the electromagnetic wave is proportional to the distance to the liquid surface.

(2) Advantages:

It does not require a transmission medium and is not affected by the atmosphere, steam, and volatile mist in the tank. It can be used for level measurement of volatile media. It adopts non-contact measurement and is not affected by the physical properties of the liquid in the tank, such as density and concentration.

(3) Expensive:

The instrument needs to set many parameters. Once a problem occurs, it is usually difficult to find out what caused it. If the antenna itself is accidentally stained with the medium, an error will be reported. If there is crystallization and icing, an error will be reported. It needs to be heated and insulated, and the antenna needs to be cleaned. The initial installation requires an empty warehouse, that is, an empty material level.

4. Ultrasonic level meter

(1) Principle:

Ultrasonic level meter is a digital level meter controlled by a microprocessor. During measurement, a pulse ultrasonic wave is emitted by a sensor (transducer). After the sound wave is reflected by the surface of the object, it is received by the same sensor and converted into an electrical signal. The distance from the sensor to the object to be measured is calculated by the time between the emission and reception of the sound wave.

(2) Advantages:

No mechanical moving parts, high reliability, simple and convenient installation, non-contact measurement, and not affected by the viscosity and density of the liquid.

(3) Disadvantages:

Low accuracy, easy to have blind spots in the test. It cannot measure pressure vessels or volatile media.

5. Capacitive level meter

(1) Principle:

The liquid level is measured by measuring the change in capacitance. It is a metal rod inserted into a liquid container. The metal rod serves as one electrode of the capacitor and the container wall serves as the other electrode. The medium between the two electrodes is the liquid and the gas above it. Therefore, the liquid level can be measured by the change in capacitance between the two electrodes. The sensitivity of the capacitive level meter mainly depends on the difference between the two dielectric constants. The metal rod electrodes are covered with an insulating layer.

(2) Advantages:

The sensor has no mechanical moving parts, simple and reliable structure; high accuracy; low power consumption at the detection end, fast dynamic response; easy maintenance and long service life. The measured medium must be a non-crystalline conductive liquid with a conductivity of not less than 10-3s/m.

(3) Disadvantages:

The unstable dielectric constant of the measured liquid will cause errors. Capacitive level meters are generally used for measuring regulating tanks and clear water tanks. (Note: Whether liquefied gas will affect the measurement is unknown and needs to be determined)

6. Static pressure (differential pressure) level gauge

(1) Principle:

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 with a pressure gauge. The pressure or differential pressure range is calculated based on the density of the measured medium and the liquid measurement range, and then a pressure gauge or differential pressure gauge with appropriate range, accuracy and other performance is selected.

(2) Advantages:

Widely popular and easy to calibrate.

(3) Disadvantages:

Greatly affected by the density and temperature of the medium, the accuracy is often poor. In order to eliminate these effects, many other test instruments are required. As a result, it is very expensive to build a complete static pressure measurement system.

7. Magnetostrictive level gauge

(1) Principle:

The electronic components at the top of the probe generate a low-voltage current pulse, which starts timing and generates a magnetic field that propagates downward along the magnetostrictive line. The float moves up and down along the measuring rod as the liquid level changes. There is a magnet inside the float, which also generates a magnetic field. When the two magnetic fields meet, the magnetostrictive line twists to form a torsional stress wave pulse. The pulse speed is known, and the pulse propagation time is calculated to correspond to the precise change in the liquid level.

(2) Advantages:

High accuracy, suitable for oil liquids and pressure gauges.

(3) Disadvantages:

Complex installation and maintenance, low market penetration. (Note: Pulse principle, suspected to have the disadvantages of radar level gauges)