Liquid level sensor (hydrostatic level gauge/liquid level transmitter/liquid level sensor/water level sensor) is a pressure sensor that measures liquid level. The static pressure input type liquid level sensor (liquid level gauge) is based on the principle that the static pressure of the measured liquid is proportional to the height of the liquid. It is an electrical signal, which is then converted into a standard electrical signal (usually 4~20mA/1~5VDC) after temperature compensation and linear correction.

Liquid level sensor classification

Divided into two categories:

The first type is contact type, including single-flange static pressure/double-flange differential pressure liquid level sensor, floating ball liquid level sensor, magnetic liquid level sensor, submersible liquid level sensor, electric inner floating ball liquid level sensor, electric Displacer level sensor, capacitive level sensor, magnetostrictive level sensor, servo level sensor, etc.

The second type is non-contact, which is divided into ultrasonic level sensors, radar level sensors, etc.

Hydrostatic submersible liquid level sensor (liquid level gauge) is suitable for liquid level measurement of various media in petrochemical, metallurgy, electric power, pharmaceutical, water supply and drainage, environmental protection and other systems and industries. Exquisite structure, simple adjustment and flexible installation provide convenience for users to use easily. 4~20mA, 0~5v, 0~10mA and other standard signal output methods can be selected by users according to their needs. The use of hydrostatic principles to measure liquid level is an important application of pressure sensors. The use of special cables with ventilation conduits in the middle and special sealing technology not only ensures the water tightness of the sensor, but also makes the reference pressure chamber communicate with the ambient pressure, thus ensuring the high precision and high stability of the measurement.

Comparison of different liquid level sensors

1. Float type liquid level sensor The float type liquid level transmitter is to change the magnetic float ball to a float, and the liquid level sensor is designed according to the Archimedes buoyancy principle. The displacer type liquid level transmitter uses the tiny metal film strain sensing technology to measure the liquid level, boundary level or density of the liquid. It can perform routine setting operations through the on-site buttons during operation.

2. Floating ball liquid level sensor The floating ball liquid level transmitter is composed of a magnetic floating ball, a measuring conduit, a signal unit, an electronic unit, a junction box and mounting parts. Generally, the specific gravity of the magnetic floating ball is less than 0.5, and it can float in the liquid. Above the surface and move up and down along the measuring pipe, the pipe is equipped with a measuring element, which can convert the measured liquid level signal into a resistance signal proportional to the liquid level change under the action of external magnetism, and convert the electronic unit into 4 ~ 20mA or other Standard signal output. The liquid level sensor is a modular circuit, which has the advantages of acid resistance, moisture resistance, shock resistance, corrosion resistance, etc. The circuit contains a constant current feedback circuit and an internal protection circuit, which can make the maximum output current not exceed 28mA, so it can reliably protect the power supply and make the secondary The meter is not damaged.

3. Static pressure liquid level sensor The transmitter works by the measurement principle of hydrostatic pressure. It generally uses a silicon pressure pressure sensor to convert the measured pressure into an electrical signal, which is then amplified by an amplifier circuit and compensated by a compensation circuit. Output in 4~20mA or 0~10mA current mode.

How the liquid level sensor works

Using the principle of static pressure measurement: when the liquid level sensor is put into a certain depth in the liquid to be measured, the pressure formula on the liquid surface of the sensor is: Ρ = ρ .g.H + Po In the formula: P : the position of the liquid surface of the transmitter Pressure ρ: Density of the liquid to be measured g: Local acceleration of gravity Po: Atmospheric pressure on the liquid surface H: The depth of the transmitter into the liquid At the same time, the pressure of the liquid is introduced into the positive pressure chamber of the sensor through the air-conducting stainless steel, and then the liquid surface The atmospheric pressure Po on the sensor is connected to the negative pressure chamber of the sensor to offset the Po on the back of the sensor, so that the pressure measured by the sensor is: ρ.g.H. Obviously, by measuring the pressure P, the liquid level depth can be obtained. Features: ◆Good stability, the long-term stability of full scale and zero position can reach 0.1%FS/year. The temperature drift is less than 0.1%FS within the compensation temperature range of 0 to 70°C, and less than 0.3%FS within the entire allowable operating temperature range.

◆It has reverse protection and current-limiting protection circuit. When the positive and negative poles are reversed during installation, the transmitter will not be damaged. When abnormal, the transmitter will automatically limit the current within 35MA.

◆Solid structure, no moving parts, high reliability and long service life.

◆Easy installation, simple structure, economical and durable.