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Full analysis of liquid level meter knowledge: functions, classification and application
Time：
2025-04-03
Liquid level meter, as a key instrument in industrial process measurement and control system, is mainly used to indicate and control liquid level. According to its function, liquid level meter can be divided into two categories: base type liquid level meter, which is mainly used for on-site indication; and remote type liquid level meter, which can convert the on-site liquid level condition into electrical signals and transmit it to the remote monitoring site, or realize remote display and control through the cooperation of liquid level transmitter and display instrument. In addition, the control of liquid level often adopts position control method. Liquid level meter usually consists of three core parts: sensor, converter and indicator, which together complete the measurement and control tasks of liquid level.
Working principle
The working principle of liquid level meter is based on static pressure measurement technology. When the liquid level transmitter is put into a certain depth in the measured liquid, the liquid surface of the sensor will be subjected to the pressure of the liquid, which can be calculated by the formula Ρ = ρ .g.H + Po, where:
Ρ represents the pressure on the liquid surface of the transmitter.
ρ is the density of the measured liquid.
g is the local acceleration of gravity.
Po is the atmospheric pressure above the liquid surface.
H is the depth of the transmitter in the liquid.
At the same time, the pressure of the liquid is introduced into the positive pressure chamber of the sensor through the gas-conducting stainless steel, and is offset by the atmospheric pressure Po connected to the negative pressure chamber on the back of the sensor. In this way, the pressure measured by the sensor is simplified to ρ.g.H. It can be seen that by measuring the pressure P, we can calculate the depth of the liquid level.
Liquid level measurement plays a vital role in chemical, electric power, metallurgical and other industrial and mining enterprises, and there are many types of liquid level meters. When choosing, it must be based on the different measuring media and working conditions. Below, we will classify and explain the liquid level meters according to their working principles:
(1) Direct reading level meters, such as glass tube level meters and glass plate level meters, which work based on the principle of communicating vessels.
(2) Differential pressure level meters, including pressure type and differential pressure type, measure the pressure generated by the liquid column or level accumulation on a certain point.
(3) Buoyancy level meters, such as magnetic float level meters and float level meters, work on the principle that the height of the float changes with the liquid level or the buoyancy of the liquid changes with the liquid level height.
(4) Electromagnetic level meters, including resistance, capacitance and inductance, measure by converting level changes into electrical changes.
(5) Nuclear radiation level meters work on the principle that the intensity of nuclear radiation changes with the thickness of the material layer when it passes through the material, and often use 7-ray technology.
(6) Acoustic wave level meters, divided into acoustic wave blocking type, reflection type and damping type, measure by the changes in acoustic impedance, acoustic wave blocking and reflection distance caused by level changes.
(7) Optical level meters work on the principle of level blocking and reflection of light waves, and the light source can be ordinary incandescent light or laser.
In addition, static pressure level meters are widely used in many systems and industries such as petrochemicals, metallurgy, and electricity, and are suitable for level measurement of various media.
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